D6142: automation: perform tasks on remote machines

indygreg (Gregory Szorc) phabricator at mercurial-scm.org
Fri Mar 15 14:26:10 EDT 2019


indygreg created this revision.
Herald added a subscriber: mercurial-devel.
Herald added a reviewer: hg-reviewers.

REVISION SUMMARY
  Sometimes you don't have access to a machine in order to
  do something. For example, you may not have access to a Windows
  machine required to build Windows binaries or run tests on that
  platform.
  
  This commit introduces a pile of code intended to help
  "automate" common tasks, like building release artifacts.
  
  In its current form, the automation code provides functionality
  for performing tasks on Windows EC2 instances.
  
  The hgautomation.aws module provides functionality for integrating
  with AWS. It manages EC2 resources such as IAM roles, EC2
  security groups, AMIs, and instances.
  
  The hgautomation.windows module provides a higher-level
  interface for performing tasks on remote Windows machines.
  
  The hgautomation.cli module provides a command-line interface to
  these higher-level primitives.
  
  I attempted to structure Windows remote machine interaction
  around Windows Remoting / PowerShell. This is kinda/sorta like
  SSH + shell, but for Windows. In theory, most of the functionality
  is cloud provider agnostic, as we should be able to use any
  established WinRM connection to interact with a remote. In
  reality, we're tightly coupled to AWS at the moment because
  I didn't want to prematurely add abstractions for a 2nd cloud
  provider. (1 was hard enough to implement.)
  
  In the aws module is code for creating an image with a fully
  functional Mercurial development environment. It contains VC9,
  VC2017, msys, and other dependencies. The image is fully capable
  of building all the existing Mercurial release artifacts and
  running tests.
  
  There are a few things that don't work. For example, running
  Windows tests with Python 3. But building the Windows release
  artifacts does work. And that was an impetus for this work.
  (Although we don't yet support code signing.)
  
  Getting this functionality to work was extremely time consuming.
  It took hours debugging permissions failures and other wonky
  behavior due to PowerShell Remoting. (The permissions model for
  PowerShell is crazy and you brush up against all kinds of
  issues because of the user/privileges of the user running
  the PowerShell and the permissions of the PowerShell session
  itself.)
  
  The functionality around AWS resource management could use some
  improving. In theory we support shared tenancy via resource
  name prefixing. In reality, we don't offer a way to configure
  this.
  
  Speaking of AWS resource management, I thought about using a tool
  like Terraform to manage resources. But at our scale, writing a
  few dozen lines of code to manage resources seemed acceptable.
  Maybe we should reconsider this if things grow out of control.
  Time will tell.
  
  Currently, emphasis is placed on Windows. But I only started
  there because it was likely to be the most difficult to implement.
  It should be relatively trivial to automate tasks on remote Linux
  machines. In fact, I have a ~1 year old script to run tests on a
  remote EC2 instance. I will likely be porting that to this new
  "framework" in the near future.
  
  1. no-check-commit because foo_bar functions

REPOSITORY
  rHG Mercurial

REVISION DETAIL
  https://phab.mercurial-scm.org/D6142

AFFECTED FILES
  contrib/automation/README.rst
  contrib/automation/automation.py
  contrib/automation/hgautomation/__init__.py
  contrib/automation/hgautomation/aws.py
  contrib/automation/hgautomation/cli.py
  contrib/automation/hgautomation/windows.py
  contrib/automation/hgautomation/winrm.py
  contrib/automation/requirements.txt
  contrib/automation/requirements.txt.in
  tests/test-check-code.t
  tests/test-check-module-imports.t
  tests/test-check-py3-compat.t

CHANGE DETAILS

diff --git a/tests/test-check-py3-compat.t b/tests/test-check-py3-compat.t
--- a/tests/test-check-py3-compat.t
+++ b/tests/test-check-py3-compat.t
@@ -5,6 +5,7 @@
 
 #if no-py3
   $ testrepohg files 'set:(**.py)' \
+  > -X contrib/automation/ \
   > -X contrib/packaging/hgpackaging/ \
   > -X contrib/packaging/inno/ \
   > -X contrib/packaging/wix/ \
diff --git a/tests/test-check-module-imports.t b/tests/test-check-module-imports.t
--- a/tests/test-check-module-imports.t
+++ b/tests/test-check-module-imports.t
@@ -18,6 +18,7 @@
   > 'tests/**.t' \
   > -X hgweb.cgi \
   > -X setup.py \
+  > -X contrib/automation/ \
   > -X contrib/debugshell.py \
   > -X contrib/hgweb.fcgi \
   > -X contrib/packaging/hg-docker \
diff --git a/tests/test-check-code.t b/tests/test-check-code.t
--- a/tests/test-check-code.t
+++ b/tests/test-check-code.t
@@ -12,6 +12,11 @@
   > -X hgext/fsmonitor/pywatchman \
   > -X mercurial/thirdparty \
   > | sed 's-\\-/-g' | "$check_code" --warnings --per-file=0 - || false
+  Skipping contrib/automation/hgautomation/__init__.py it has no-che?k-code (glob)
+  Skipping contrib/automation/hgautomation/aws.py it has no-che?k-code (glob)
+  Skipping contrib/automation/hgautomation/cli.py it has no-che?k-code (glob)
+  Skipping contrib/automation/hgautomation/windows.py it has no-che?k-code (glob)
+  Skipping contrib/automation/hgautomation/winrm.py it has no-che?k-code (glob)
   Skipping contrib/packaging/hgpackaging/downloads.py it has no-che?k-code (glob)
   Skipping contrib/packaging/hgpackaging/inno.py it has no-che?k-code (glob)
   Skipping contrib/packaging/hgpackaging/py2exe.py it has no-che?k-code (glob)
diff --git a/contrib/automation/requirements.txt.in b/contrib/automation/requirements.txt.in
new file mode 100644
--- /dev/null
+++ b/contrib/automation/requirements.txt.in
@@ -0,0 +1,2 @@
+boto3
+pypsrp
diff --git a/contrib/automation/requirements.txt b/contrib/automation/requirements.txt
new file mode 100644
--- /dev/null
+++ b/contrib/automation/requirements.txt
@@ -0,0 +1,119 @@
+#
+# This file is autogenerated by pip-compile
+# To update, run:
+#
+#    pip-compile -U --generate-hashes --output-file contrib/automation/requirements.txt contrib/automation/requirements.txt.in
+#
+asn1crypto==0.24.0 \
+    --hash=sha256:2f1adbb7546ed199e3c90ef23ec95c5cf3585bac7d11fb7eb562a3fe89c64e87 \
+    --hash=sha256:9d5c20441baf0cb60a4ac34cc447c6c189024b6b4c6cd7877034f4965c464e49 \
+    # via cryptography
+boto3==1.9.111 \
+    --hash=sha256:06414c75d1f62af7d04fd652b38d1e4fd3cfd6b35bad978466af88e2aaecd00d \
+    --hash=sha256:f3b77dff382374773d02411fa47ee408f4f503aeebd837fd9dc9ed8635bc5e8e
+botocore==1.12.111 \
+    --hash=sha256:6af473c52d5e3e7ff82de5334e9fee96b2d5ec2df5d78bc00cd9937e2573a7a8 \
+    --hash=sha256:9f5123c7be704b17aeacae99b5842ab17bda1f799dd29134de8c70e0a50a45d7 \
+    # via boto3, s3transfer
+certifi==2019.3.9 \
+    --hash=sha256:59b7658e26ca9c7339e00f8f4636cdfe59d34fa37b9b04f6f9e9926b3cece1a5 \
+    --hash=sha256:b26104d6835d1f5e49452a26eb2ff87fe7090b89dfcaee5ea2212697e1e1d7ae \
+    # via requests
+cffi==1.12.2 \
+    --hash=sha256:00b97afa72c233495560a0793cdc86c2571721b4271c0667addc83c417f3d90f \
+    --hash=sha256:0ba1b0c90f2124459f6966a10c03794082a2f3985cd699d7d63c4a8dae113e11 \
+    --hash=sha256:0bffb69da295a4fc3349f2ec7cbe16b8ba057b0a593a92cbe8396e535244ee9d \
+    --hash=sha256:21469a2b1082088d11ccd79dd84157ba42d940064abbfa59cf5f024c19cf4891 \
+    --hash=sha256:2e4812f7fa984bf1ab253a40f1f4391b604f7fc424a3e21f7de542a7f8f7aedf \
+    --hash=sha256:2eac2cdd07b9049dd4e68449b90d3ef1adc7c759463af5beb53a84f1db62e36c \
+    --hash=sha256:2f9089979d7456c74d21303c7851f158833d48fb265876923edcb2d0194104ed \
+    --hash=sha256:3dd13feff00bddb0bd2d650cdb7338f815c1789a91a6f68fdc00e5c5ed40329b \
+    --hash=sha256:4065c32b52f4b142f417af6f33a5024edc1336aa845b9d5a8d86071f6fcaac5a \
+    --hash=sha256:51a4ba1256e9003a3acf508e3b4f4661bebd015b8180cc31849da222426ef585 \
+    --hash=sha256:59888faac06403767c0cf8cfb3f4a777b2939b1fbd9f729299b5384f097f05ea \
+    --hash=sha256:59c87886640574d8b14910840327f5cd15954e26ed0bbd4e7cef95fa5aef218f \
+    --hash=sha256:610fc7d6db6c56a244c2701575f6851461753c60f73f2de89c79bbf1cc807f33 \
+    --hash=sha256:70aeadeecb281ea901bf4230c6222af0248c41044d6f57401a614ea59d96d145 \
+    --hash=sha256:71e1296d5e66c59cd2c0f2d72dc476d42afe02aeddc833d8e05630a0551dad7a \
+    --hash=sha256:8fc7a49b440ea752cfdf1d51a586fd08d395ff7a5d555dc69e84b1939f7ddee3 \
+    --hash=sha256:9b5c2afd2d6e3771d516045a6cfa11a8da9a60e3d128746a7fe9ab36dfe7221f \
+    --hash=sha256:9c759051ebcb244d9d55ee791259ddd158188d15adee3c152502d3b69005e6bd \
+    --hash=sha256:b4d1011fec5ec12aa7cc10c05a2f2f12dfa0adfe958e56ae38dc140614035804 \
+    --hash=sha256:b4f1d6332339ecc61275bebd1f7b674098a66fea11a00c84d1c58851e618dc0d \
+    --hash=sha256:c030cda3dc8e62b814831faa4eb93dd9a46498af8cd1d5c178c2de856972fd92 \
+    --hash=sha256:c2e1f2012e56d61390c0e668c20c4fb0ae667c44d6f6a2eeea5d7148dcd3df9f \
+    --hash=sha256:c37c77d6562074452120fc6c02ad86ec928f5710fbc435a181d69334b4de1d84 \
+    --hash=sha256:c8149780c60f8fd02752d0429246088c6c04e234b895c4a42e1ea9b4de8d27fb \
+    --hash=sha256:cbeeef1dc3c4299bd746b774f019de9e4672f7cc666c777cd5b409f0b746dac7 \
+    --hash=sha256:e113878a446c6228669144ae8a56e268c91b7f1fafae927adc4879d9849e0ea7 \
+    --hash=sha256:e21162bf941b85c0cda08224dade5def9360f53b09f9f259adb85fc7dd0e7b35 \
+    --hash=sha256:fb6934ef4744becbda3143d30c6604718871495a5e36c408431bf33d9c146889 \
+    # via cryptography
+chardet==3.0.4 \
+    --hash=sha256:84ab92ed1c4d4f16916e05906b6b75a6c0fb5db821cc65e70cbd64a3e2a5eaae \
+    --hash=sha256:fc323ffcaeaed0e0a02bf4d117757b98aed530d9ed4531e3e15460124c106691 \
+    # via requests
+cryptography==2.6.1 \
+    --hash=sha256:066f815f1fe46020877c5983a7e747ae140f517f1b09030ec098503575265ce1 \
+    --hash=sha256:210210d9df0afba9e000636e97810117dc55b7157c903a55716bb73e3ae07705 \
+    --hash=sha256:26c821cbeb683facb966045e2064303029d572a87ee69ca5a1bf54bf55f93ca6 \
+    --hash=sha256:2afb83308dc5c5255149ff7d3fb9964f7c9ee3d59b603ec18ccf5b0a8852e2b1 \
+    --hash=sha256:2db34e5c45988f36f7a08a7ab2b69638994a8923853dec2d4af121f689c66dc8 \
+    --hash=sha256:409c4653e0f719fa78febcb71ac417076ae5e20160aec7270c91d009837b9151 \
+    --hash=sha256:45a4f4cf4f4e6a55c8128f8b76b4c057027b27d4c67e3fe157fa02f27e37830d \
+    --hash=sha256:48eab46ef38faf1031e58dfcc9c3e71756a1108f4c9c966150b605d4a1a7f659 \
+    --hash=sha256:6b9e0ae298ab20d371fc26e2129fd683cfc0cfde4d157c6341722de645146537 \
+    --hash=sha256:6c4778afe50f413707f604828c1ad1ff81fadf6c110cb669579dea7e2e98a75e \
+    --hash=sha256:8c33fb99025d353c9520141f8bc989c2134a1f76bac6369cea060812f5b5c2bb \
+    --hash=sha256:9873a1760a274b620a135054b756f9f218fa61ca030e42df31b409f0fb738b6c \
+    --hash=sha256:9b069768c627f3f5623b1cbd3248c5e7e92aec62f4c98827059eed7053138cc9 \
+    --hash=sha256:9e4ce27a507e4886efbd3c32d120db5089b906979a4debf1d5939ec01b9dd6c5 \
+    --hash=sha256:acb424eaca214cb08735f1a744eceb97d014de6530c1ea23beb86d9c6f13c2ad \
+    --hash=sha256:c8181c7d77388fe26ab8418bb088b1a1ef5fde058c6926790c8a0a3d94075a4a \
+    --hash=sha256:d4afbb0840f489b60f5a580a41a1b9c3622e08ecb5eec8614d4fb4cd914c4460 \
+    --hash=sha256:d9ed28030797c00f4bc43c86bf819266c76a5ea61d006cd4078a93ebf7da6bfd \
+    --hash=sha256:e603aa7bb52e4e8ed4119a58a03b60323918467ef209e6ff9db3ac382e5cf2c6 \
+    # via pypsrp
+docutils==0.14 \
+    --hash=sha256:02aec4bd92ab067f6ff27a38a38a41173bf01bed8f89157768c1573f53e474a6 \
+    --hash=sha256:51e64ef2ebfb29cae1faa133b3710143496eca21c530f3f71424d77687764274 \
+    --hash=sha256:7a4bd47eaf6596e1295ecb11361139febe29b084a87bf005bf899f9a42edc3c6 \
+    # via botocore
+idna==2.8 \
+    --hash=sha256:c357b3f628cf53ae2c4c05627ecc484553142ca23264e593d327bcde5e9c3407 \
+    --hash=sha256:ea8b7f6188e6fa117537c3df7da9fc686d485087abf6ac197f9c46432f7e4a3c \
+    # via requests
+jmespath==0.9.4 \
+    --hash=sha256:3720a4b1bd659dd2eecad0666459b9788813e032b83e7ba58578e48254e0a0e6 \
+    --hash=sha256:bde2aef6f44302dfb30320115b17d030798de8c4110e28d5cf6cf91a7a31074c \
+    # via boto3, botocore
+ntlm-auth==1.2.0 \
+    --hash=sha256:7bc02a3fbdfee7275d3dc20fce8028ed8eb6d32364637f28be9e9ae9160c6d5c \
+    --hash=sha256:9b13eaf88f16a831637d75236a93d60c0049536715aafbf8190ba58a590b023e \
+    # via pypsrp
+pycparser==2.19 \
+    --hash=sha256:a988718abfad80b6b157acce7bf130a30876d27603738ac39f140993246b25b3 \
+    # via cffi
+pypsrp==0.3.1 \
+    --hash=sha256:309853380fe086090a03cc6662a778ee69b1cae355ae4a932859034fd76e9d0b \
+    --hash=sha256:90f946254f547dc3493cea8493c819ab87e152a755797c93aa2668678ba8ae85
+python-dateutil==2.8.0 \
+    --hash=sha256:7e6584c74aeed623791615e26efd690f29817a27c73085b78e4bad02493df2fb \
+    --hash=sha256:c89805f6f4d64db21ed966fda138f8a5ed7a4fdbc1a8ee329ce1b74e3c74da9e \
+    # via botocore
+requests==2.21.0 \
+    --hash=sha256:502a824f31acdacb3a35b6690b5fbf0bc41d63a24a45c4004352b0242707598e \
+    --hash=sha256:7bf2a778576d825600030a110f3c0e3e8edc51dfaafe1c146e39a2027784957b \
+    # via pypsrp
+s3transfer==0.2.0 \
+    --hash=sha256:7b9ad3213bff7d357f888e0fab5101b56fa1a0548ee77d121c3a3dbfbef4cb2e \
+    --hash=sha256:f23d5cb7d862b104401d9021fc82e5fa0e0cf57b7660a1331425aab0c691d021 \
+    # via boto3
+six==1.12.0 \
+    --hash=sha256:3350809f0555b11f552448330d0b52d5f24c91a322ea4a15ef22629740f3761c \
+    --hash=sha256:d16a0141ec1a18405cd4ce8b4613101da75da0e9a7aec5bdd4fa804d0e0eba73 \
+    # via cryptography, pypsrp, python-dateutil
+urllib3==1.24.1 \
+    --hash=sha256:61bf29cada3fc2fbefad4fdf059ea4bd1b4a86d2b6d15e1c7c0b582b9752fe39 \
+    --hash=sha256:de9529817c93f27c8ccbfead6985011db27bd0ddfcdb2d86f3f663385c6a9c22 \
+    # via botocore, requests
diff --git a/contrib/automation/hgautomation/winrm.py b/contrib/automation/hgautomation/winrm.py
new file mode 100644
--- /dev/null
+++ b/contrib/automation/hgautomation/winrm.py
@@ -0,0 +1,82 @@
+# winrm.py - Interact with Windows Remote Management (WinRM)
+#
+# Copyright 2019 Gregory Szorc <gregory.szorc at gmail.com>
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+
+# no-check-code because Python 3 native.
+
+import logging
+import pprint
+import time
+
+from pypsrp.client import (
+    Client,
+)
+from pypsrp.powershell import (
+    PowerShell,
+    PSInvocationState,
+    RunspacePool,
+)
+import requests.exceptions
+
+
+logger = logging.getLogger(__name__)
+
+
+def wait_for_winrm(host, username, password, timeout=120, ssl=False):
+    """Wait for the Windows Remoting (WinRM) service to become available.
+
+    Returns a ``psrpclient.Client`` instance.
+    """
+
+    end_time = time.time() + timeout
+
+    while True:
+        try:
+            client = Client(host, username=username, password=password,
+                            ssl=ssl, connection_timeout=5)
+            client.execute_cmd('echo "hello world"')
+            return client
+        except requests.exceptions.ConnectionError:
+            if time.time() >= end_time:
+                raise
+
+            time.sleep(1)
+
+
+def format_object(o):
+    if isinstance(o, str):
+        return o
+
+    try:
+        o = str(o)
+    except TypeError:
+        o = pprint.pformat(o.extended_properties)
+
+    return o
+
+
+def run_powershell(client, script):
+    with RunspacePool(client.wsman) as pool:
+        ps = PowerShell(pool)
+        ps.add_script(script)
+
+        ps.begin_invoke()
+
+        while ps.state == PSInvocationState.RUNNING:
+            ps.poll_invoke()
+            for o in ps.output:
+                print(format_object(o))
+
+            ps.output[:] = []
+
+        ps.end_invoke()
+
+        for o in ps.output:
+            print(format_object(o))
+
+        if ps.state == PSInvocationState.FAILED:
+            raise Exception('PowerShell execution failed: %s' %
+                            ' '.join(map(format_object, ps.streams.error)))
diff --git a/contrib/automation/hgautomation/windows.py b/contrib/automation/hgautomation/windows.py
new file mode 100644
--- /dev/null
+++ b/contrib/automation/hgautomation/windows.py
@@ -0,0 +1,287 @@
+# windows.py - Automation specific to Windows
+#
+# Copyright 2019 Gregory Szorc <gregory.szorc at gmail.com>
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+
+# no-check-code because Python 3 native.
+
+import os
+import pathlib
+import re
+import subprocess
+import tempfile
+
+from .winrm import (
+    run_powershell,
+)
+
+
+# PowerShell commands to activate a Visual Studio 2008 environment.
+# This is essentially a port of vcvarsall.bat to PowerShell.
+ACTIVATE_VC9_AMD64 = r'''
+Write-Output "activating Visual Studio 2008 environment for AMD64"
+$root = "$env:LOCALAPPDATA\Programs\Common\Microsoft\Visual C++ for Python\9.0"
+$Env:VCINSTALLDIR = "${root}\VC\"
+$Env:WindowsSdkDir = "${root}\WinSDK\"
+$Env:PATH = "${root}\VC\Bin\amd64;${root}\WinSDK\Bin\x64;${root}\WinSDK\Bin;$Env:PATH"
+$Env:INCLUDE = "${root}\VC\Include;${root}\WinSDK\Include;$Env:PATH"
+$Env:LIB = "${root}\VC\Lib\amd64;${root}\WinSDK\Lib\x64;$Env:LIB"
+$Env:LIBPATH = "${root}\VC\Lib\amd64;${root}\WinSDK\Lib\x64;$Env:LIBPATH"
+'''.lstrip()
+
+ACTIVATE_VC9_X86 = r'''
+Write-Output "activating Visual Studio 2008 environment for x86"
+$root = "$env:LOCALAPPDATA\Programs\Common\Microsoft\Visual C++ for Python\9.0"
+$Env:VCINSTALLDIR = "${root}\VC\"
+$Env:WindowsSdkDir = "${root}\WinSDK\"
+$Env:PATH = "${root}\VC\Bin;${root}\WinSDK\Bin;$Env:PATH"
+$Env:INCLUDE = "${root}\VC\Include;${root}\WinSDK\Include;$Env:INCLUDE"
+$Env:LIB = "${root}\VC\Lib;${root}\WinSDK\Lib;$Env:LIB"
+$Env:LIBPATH = "${root}\VC\lib;${root}\WinSDK\Lib:$Env:LIBPATH"
+'''.lstrip()
+
+HG_PURGE = r'''
+$Env:PATH = "C:\hgdev\venv-bootstrap\Scripts;$Env:PATH"
+Set-Location C:\hgdev\src
+hg.exe --config extensions.purge= purge --all
+if ($LASTEXITCODE -ne 0) {
+    throw "process exited non-0: $LASTEXITCODE"
+}
+Write-Output "purged Mercurial repo"
+'''
+
+HG_UPDATE_CLEAN = r'''
+$Env:PATH = "C:\hgdev\venv-bootstrap\Scripts;$Env:PATH"
+Set-Location C:\hgdev\src
+hg.exe --config extensions.purge= purge --all
+if ($LASTEXITCODE -ne 0) {{
+    throw "process exited non-0: $LASTEXITCODE"
+}}
+hg.exe update -C {revision}
+if ($LASTEXITCODE -ne 0) {{
+    throw "process exited non-0: $LASTEXITCODE"
+}}
+hg.exe log -r .
+Write-Output "updated Mercurial working directory to {revision}"
+'''.lstrip()
+
+BUILD_INNO = r'''
+Set-Location C:\hgdev\src
+$python = "C:\hgdev\python27-{arch}\python.exe"
+C:\hgdev\python37-x64\python.exe contrib\packaging\inno\build.py --python $python
+if ($LASTEXITCODE -ne 0) {{
+    throw "process exited non-0: $LASTEXITCODE"
+}}
+'''.lstrip()
+
+BUILD_WHEEL = r'''
+Set-Location C:\hgdev\src
+C:\hgdev\python27-{arch}\Scripts\pip.exe wheel --wheel-dir dist .
+if ($LASTEXITCODE -ne 0) {{
+    throw "process exited non-0: $LASTEXITCODE"
+}}
+'''
+
+BUILD_WIX = r'''
+Set-Location C:\hgdev\src
+$python = "C:\hgdev\python27-{arch}\python.exe"
+C:\hgdev\python37-x64\python.exe contrib\packaging\wix\build.py --python $python {extra_args}
+if ($LASTEXITCODE -ne 0) {{
+    throw "process exited non-0: $LASTEXITCODE"
+}}
+'''
+
+RUN_TESTS = r'''
+C:\hgdev\MinGW\msys\1.0\bin\sh.exe --login -c "cd /c/hgdev/src/tests && /c/hgdev/{python_path}/python.exe run-tests.py {test_flags}"
+if ($LASTEXITCODE -ne 0) {{
+    throw "process exited non-0: $LASTEXITCODE"
+}}
+'''
+
+
+def get_vc_prefix(arch):
+    if arch == 'x86':
+        return ACTIVATE_VC9_X86
+    elif arch == 'x64':
+        return ACTIVATE_VC9_AMD64
+    else:
+        raise ValueError('illegal arch: %s; must be x86 or x64' % arch)
+
+
+def fix_authorized_keys_permissions(winrm_client, path):
+    commands = [
+        '$ErrorActionPreference = "Stop"',
+        'Repair-AuthorizedKeyPermission -FilePath %s -Confirm:$false' % path,
+        'icacls %s /remove:g "NT Service\sshd"' % path,
+    ]
+
+    run_powershell(winrm_client, '\n'.join(commands))
+
+
+def synchronize_hg(hg_repo: pathlib.Path, revision: str, ec2_instance):
+    """Synchronize local Mercurial repo to remote EC2 instance."""
+
+    winrm_client = ec2_instance.winrm_client
+
+    with tempfile.TemporaryDirectory() as temp_dir:
+        temp_dir = pathlib.Path(temp_dir)
+
+        ssh_dir = temp_dir / '.ssh'
+        ssh_dir.mkdir()
+        ssh_dir.chmod(0o0700)
+
+        # Generate SSH key to use for communication.
+        subprocess.run([
+            'ssh-keygen', '-t', 'rsa', '-b', '4096', '-N', '',
+            '-f', str(ssh_dir / 'id_rsa')],
+            check=True, capture_output=True)
+
+        # Add it to ~/.ssh/authorized_keys on remote.
+        # This assumes the file doesn't already exist.
+        authorized_keys = r'c:\Users\Administrator\.ssh\authorized_keys'
+        winrm_client.execute_cmd(r'mkdir c:\Users\Administrator\.ssh')
+        winrm_client.copy(str(ssh_dir / 'id_rsa.pub'), authorized_keys)
+        fix_authorized_keys_permissions(winrm_client, authorized_keys)
+
+        public_ip = ec2_instance.public_ip_address
+
+        ssh_config = temp_dir / '.ssh' / 'config'
+
+        with open(ssh_config, 'w', encoding='utf-8') as fh:
+            fh.write('Host %s\n' % public_ip)
+            fh.write('  User Administrator\n')
+            fh.write('  StrictHostKeyChecking no\n')
+            fh.write('  UserKnownHostsFile %s\n' % (ssh_dir / 'known_hosts'))
+            fh.write('  IdentityFile %s\n' % (ssh_dir / 'id_rsa'))
+
+        env = dict(os.environ)
+        env['HGPLAIN'] = '1'
+        env['HGENCODING'] = 'utf-8'
+
+        hg_bin = hg_repo / 'hg'
+
+        res = subprocess.run(
+            ['python2.7', str(hg_bin), 'log', '-r', revision, '-T', '{node}'],
+            cwd=str(hg_repo), env=env, check=True, capture_output=True)
+
+        full_revision = res.stdout.decode('ascii')
+
+        args = [
+            'python2.7', hg_bin,
+            '--config', 'ui.ssh=ssh -F %s' % ssh_config,
+            '--config', 'ui.remotecmd=c:/hgdev/venv-bootstrap/Scripts/hg.exe',
+            'push', '-r', full_revision, 'ssh://%s/c:/hgdev/src' % public_ip,
+        ]
+
+        subprocess.run(args, cwd=str(hg_repo), env=env, check=True)
+
+        run_powershell(winrm_client,
+                       HG_UPDATE_CLEAN.format(revision=full_revision))
+
+        # TODO detect dirty local working directory and synchronize accordingly.
+
+
+def purge_hg(winrm_client):
+    """Purge the Mercurial source repository on an EC2 instance."""
+    run_powershell(winrm_client, HG_PURGE)
+
+
+def find_latest_dist(winrm_client, pattern):
+    """Find path to newest file in dist/ directory matching a pattern."""
+
+    res = winrm_client.execute_ps(
+        '$v = Get-ChildItem -Path C:\hgdev\src\dist -Filter "%s" '
+        '| Sort-Object LastWriteTime -Descending '
+        '| Select-Object -First 1\n'
+        '$v.name' % pattern
+    )
+    return res[0]
+
+
+def copy_latest_dist(winrm_client, pattern, dest_path):
+    """Copy latest file matching pattern in dist/ directory.
+
+    Given a WinRM client and a file pattern, find the latest file on the remote
+    matching that pattern and copy it to the ``dest_path`` directory on the
+    local machine.
+    """
+    latest = find_latest_dist(winrm_client, pattern)
+    source = r'C:\hgdev\src\dist\%s' % latest
+    dest = dest_path / latest
+    print('copying %s to %s' % (source, dest))
+    winrm_client.fetch(source, str(dest))
+
+
+def build_inno_installer(winrm_client, arch: str, dest_path: pathlib.Path,
+                         version=None):
+    """Build the Inno Setup installer on a remote machine.
+
+    Using a WinRM client, remote commands are executed to build
+    a Mercurial Inno Setup installer.
+    """
+    print('building Inno Setup installer for %s' % arch)
+
+    extra_args = []
+    if version:
+        extra_args.extend(['--version', version])
+
+    ps = get_vc_prefix(arch) + BUILD_INNO.format(arch=arch,
+                                                 extra_args=' '.join(extra_args))
+    run_powershell(winrm_client, ps)
+    copy_latest_dist(winrm_client, '*.exe', dest_path)
+
+
+def build_wheel(winrm_client, arch: str, dest_path: pathlib.Path):
+    """Build Python wheels on a remote machine.
+
+    Using a WinRM client, remote commands are executed to build a Python wheel
+    for Mercurial.
+    """
+    print('Building Windows wheel for %s' % arch)
+    ps = get_vc_prefix(arch) + BUILD_WHEEL.format(arch=arch)
+    run_powershell(winrm_client, ps)
+    copy_latest_dist(winrm_client, '*.whl', dest_path)
+
+
+def build_wix_installer(winrm_client, arch: str, dest_path: pathlib.Path,
+                        version=None):
+    """Build the WiX installer on a remote machine.
+
+    Using a WinRM client, remote commands are executed to build a WiX installer.
+    """
+    print('Building WiX installer for %s' % arch)
+    extra_args = []
+    if version:
+        extra_args.extend(['--version', version])
+
+    ps = get_vc_prefix(arch) + BUILD_WIX.format(arch=arch,
+                                                extra_args=' '.join(extra_args))
+    run_powershell(winrm_client, ps)
+    copy_latest_dist(winrm_client, '*.msi', dest_path)
+
+
+def run_tests(winrm_client, python_version, arch, test_flags=''):
+    """Run tests on a remote Windows machine.
+
+    ``python_version`` is a ``X.Y`` string like ``2.7`` or ``3.7``.
+    ``arch`` is ``x86`` or ``x64``.
+    ``test_flags`` is a str representing extra arguments to pass to
+    ``run-tests.py``.
+    """
+    if not re.match('\d\.\d', python_version):
+        raise ValueError('python_version must be \d.\d; got %s' %
+                         python_version)
+
+    if arch not in ('x86', 'x64'):
+        raise ValueError('arch must be x86 or x64; got %s' % arch)
+
+    python_path = 'python%s-%s' % (python_version.replace('.', ''), arch)
+
+    ps = RUN_TESTS.format(
+        python_path=python_path,
+        test_flags=test_flags or '',
+    )
+
+    run_powershell(winrm_client, ps)
diff --git a/contrib/automation/hgautomation/cli.py b/contrib/automation/hgautomation/cli.py
new file mode 100644
--- /dev/null
+++ b/contrib/automation/hgautomation/cli.py
@@ -0,0 +1,273 @@
+# cli.py - Command line interface for automation
+#
+# Copyright 2019 Gregory Szorc <gregory.szorc at gmail.com>
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+
+# no-check-code because Python 3 native.
+
+import argparse
+import os
+import pathlib
+
+from . import (
+    aws,
+    HGAutomation,
+    windows,
+)
+
+
+SOURCE_ROOT = pathlib.Path(os.path.abspath(__file__)).parent.parent.parent.parent
+DIST_PATH = SOURCE_ROOT / 'dist'
+
+
+def bootstrap_windows_dev(hga: HGAutomation, aws_region):
+    c = hga.aws_connection(aws_region)
+    image = aws.ensure_windows_dev_ami(c)
+    print('Windows development AMI available as %s' % image.id)
+
+
+def build_inno(hga: HGAutomation, aws_region, arch, revision, version):
+    c = hga.aws_connection(aws_region)
+    image = aws.ensure_windows_dev_ami(c)
+    DIST_PATH.mkdir(exist_ok=True)
+
+    with aws.temporary_windows_dev_instances(c, image, 't3.medium') as insts:
+        instance = insts[0]
+
+        windows.synchronize_hg(SOURCE_ROOT, revision, instance)
+
+        for a in arch:
+            windows.build_inno_installer(instance.winrm_client, a,
+                                         DIST_PATH,
+                                         version=version)
+
+
+def build_wix(hga: HGAutomation, aws_region, arch, revision, version):
+    c = hga.aws_connection(aws_region)
+    image = aws.ensure_windows_dev_ami(c)
+    DIST_PATH.mkdir(exist_ok=True)
+
+    with aws.temporary_windows_dev_instances(c, image, 't3.medium') as insts:
+        instance = insts[0]
+
+        windows.synchronize_hg(SOURCE_ROOT, revision, instance)
+
+        for a in arch:
+            windows.build_wix_installer(instance.winrm_client, a,
+                                        DIST_PATH, version=version)
+
+
+def build_windows_wheel(hga: HGAutomation, aws_region, arch, revision):
+    c = hga.aws_connection(aws_region)
+    image = aws.ensure_windows_dev_ami(c)
+    DIST_PATH.mkdir(exist_ok=True)
+
+    with aws.temporary_windows_dev_instances(c, image, 't3.medium') as insts:
+        instance = insts[0]
+
+        windows.synchronize_hg(SOURCE_ROOT, revision, instance)
+
+        for a in arch:
+            windows.build_wheel(instance.winrm_client, a, DIST_PATH)
+
+
+def build_all_windows_packages(hga: HGAutomation, aws_region, revision):
+    c = hga.aws_connection(aws_region)
+    image = aws.ensure_windows_dev_ami(c)
+    DIST_PATH.mkdir(exist_ok=True)
+
+    with aws.temporary_windows_dev_instances(c, image, 't3.medium') as insts:
+        instance = insts[0]
+
+        winrm_client = instance.winrm_client
+
+        windows.synchronize_hg(SOURCE_ROOT, revision, instance)
+
+        for arch in ('x86', 'x64'):
+            windows.purge_hg(winrm_client)
+            windows.build_wheel(winrm_client, arch, DIST_PATH)
+            windows.purge_hg(winrm_client)
+            windows.build_inno_installer(winrm_client, arch, DIST_PATH)
+            windows.purge_hg(winrm_client)
+            windows.build_wix_installer(winrm_client, arch, DIST_PATH)
+
+
+def terminate_ec2_instances(hga: HGAutomation, aws_region):
+    c = hga.aws_connection(aws_region)
+    aws.terminate_ec2_instances(c.ec2resource)
+
+
+def purge_ec2_resources(hga: HGAutomation, aws_region):
+    c = hga.aws_connection(aws_region)
+    aws.remove_resources(c)
+
+
+def run_tests_windows(hga: HGAutomation, aws_region, instance_type,
+                      python_version, arch, test_flags):
+    c = hga.aws_connection(aws_region)
+    image = aws.ensure_windows_dev_ami(c)
+
+    with aws.temporary_windows_dev_instances(c, image, instance_type,
+                                             disable_antivirus=True) as insts:
+        instance = insts[0]
+
+        windows.synchronize_hg(SOURCE_ROOT, '.', instance)
+        windows.run_tests(instance.winrm_client, python_version, arch,
+                          test_flags)
+
+
+def get_parser():
+    parser = argparse.ArgumentParser()
+
+    parser.add_argument(
+        '--state-path',
+        default='~/.hgautomation',
+        help='Path for local state files',
+    )
+    parser.add_argument(
+        '--aws-region',
+        help='AWS region to use',
+        default='us-west-1',
+    )
+
+    subparsers = parser.add_subparsers()
+
+    sp = subparsers.add_parser(
+        'bootstrap-windows-dev',
+        help='Bootstrap the Windows development environment',
+    )
+    sp.set_defaults(func=bootstrap_windows_dev)
+
+    sp = subparsers.add_parser(
+        'build-all-windows-packages',
+        help='Build all Windows packages',
+    )
+    sp.add_argument(
+        '--revision',
+        help='Mercurial revision to build',
+        default='.',
+    )
+    sp.set_defaults(func=build_all_windows_packages)
+
+    sp = subparsers.add_parser(
+        'build-inno',
+        help='Build Inno Setup installer(s)',
+    )
+    sp.add_argument(
+        '--arch',
+        help='Architecture to build for',
+        choices={'x86', 'x64'},
+        nargs='*',
+        default=['x64'],
+    )
+    sp.add_argument(
+        '--revision',
+        help='Mercurial revision to build',
+        default='.',
+    )
+    sp.add_argument(
+        '--version',
+        help='Mercurial version string to use in installer',
+    )
+    sp.set_defaults(func=build_inno)
+
+    sp = subparsers.add_parser(
+        'build-windows-wheel',
+        help='Build Windows wheel(s)',
+    )
+    sp.add_argument(
+        '--arch',
+        help='Architecture to build for',
+        choices={'x86', 'x64'},
+        nargs='*',
+        default=['x64'],
+    )
+    sp.add_argument(
+        '--revision',
+        help='Mercurial revision to build',
+        default='.',
+    )
+    sp.set_defaults(func=build_windows_wheel)
+
+    sp = subparsers.add_parser(
+        'build-wix',
+        help='Build WiX installer(s)'
+    )
+    sp.add_argument(
+        '--arch',
+        help='Architecture to build for',
+        choices={'x86', 'x64'},
+        nargs='*',
+        default=['x64'],
+    )
+    sp.add_argument(
+        '--revision',
+        help='Mercurial revision to build',
+        default='.',
+    )
+    sp.add_argument(
+        '--version',
+        help='Mercurial version string to use in installer',
+    )
+    sp.set_defaults(func=build_wix)
+
+    sp = subparsers.add_parser(
+        'terminate-ec2-instances',
+        help='Terminate all active EC2 instances managed by us',
+    )
+    sp.set_defaults(func=terminate_ec2_instances)
+
+    sp = subparsers.add_parser(
+        'purge-ec2-resources',
+        help='Purge all EC2 resources managed by us',
+    )
+    sp.set_defaults(func=purge_ec2_resources)
+
+    sp = subparsers.add_parser(
+        'run-tests-windows',
+        help='Run tests on Windows',
+    )
+    sp.add_argument(
+        '--instance-type',
+        help='EC2 instance type to use',
+        default='t3.medium',
+    )
+    sp.add_argument(
+        '--python-version',
+        help='Python version to use',
+        choices={'2.7', '3.5', '3.6', '3.7', '3.8'},
+        default='2.7',
+    )
+    sp.add_argument(
+        '--arch',
+        help='Architecture to test',
+        choices={'x86', 'x64'},
+        default='x64',
+    )
+    sp.add_argument(
+        '--test-flags',
+        help='Extra command line flags to pass to run-tests.py',
+    )
+    sp.set_defaults(func=run_tests_windows)
+
+    return parser
+
+
+def main():
+    parser = get_parser()
+    args = parser.parse_args()
+
+    local_state_path = pathlib.Path(os.path.expanduser(args.state_path))
+    automation = HGAutomation(local_state_path)
+
+    if not hasattr(args, 'func'):
+        parser.print_help()
+        return
+
+    kwargs = dict(vars(args))
+    del kwargs['func']
+    del kwargs['state_path']
+
+    args.func(automation, **kwargs)
diff --git a/contrib/automation/hgautomation/aws.py b/contrib/automation/hgautomation/aws.py
new file mode 100644
--- /dev/null
+++ b/contrib/automation/hgautomation/aws.py
@@ -0,0 +1,879 @@
+# aws.py - Automation code for Amazon Web Services
+#
+# Copyright 2019 Gregory Szorc <gregory.szorc at gmail.com>
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+
+# no-check-code because Python 3 native.
+
+import contextlib
+import copy
+import hashlib
+import json
+import os
+import pathlib
+import subprocess
+import time
+
+import boto3
+import botocore.exceptions
+
+from .winrm import (
+    run_powershell,
+    wait_for_winrm,
+)
+
+
+SOURCE_ROOT = pathlib.Path(os.path.abspath(__file__)).parent.parent.parent.parent
+
+INSTALL_WINDOWS_DEPENDENCIES = (SOURCE_ROOT / 'contrib' /
+                                'install-windows-dependencies.ps1')
+
+
+KEY_PAIRS = {
+    'automation',
+}
+
+
+SECURITY_GROUPS = {
+    'windows-dev-1': {
+        'description': 'Mercurial Windows instances that perform build automation',
+        'ingress': [
+            {
+                'FromPort': 22,
+                'ToPort': 22,
+                'IpProtocol': 'tcp',
+                'IpRanges': [
+                    {
+                        'CidrIp': '0.0.0.0/0',
+                        'Description': 'SSH from entire Internet',
+                    },
+                ],
+            },
+            {
+                'FromPort': 3389,
+                'ToPort': 3389,
+                'IpProtocol': 'tcp',
+                'IpRanges': [
+                    {
+                        'CidrIp': '0.0.0.0/0',
+                        'Description': 'RDP from entire Internet',
+                    },
+                ],
+
+            },
+            {
+                'FromPort': 5985,
+                'ToPort': 5986,
+                'IpProtocol': 'tcp',
+                'IpRanges': [
+                    {
+                        'CidrIp': '0.0.0.0/0',
+                        'Description': 'PowerShell Remoting (Windows Remote Management)',
+                    },
+                ],
+            }
+        ],
+    },
+}
+
+
+IAM_ROLES = {
+    'ephemeral-ec2-role-1': {
+        'description': 'Mercurial temporary EC2 instances',
+        'policy_arns': [
+            'arn:aws:iam::aws:policy/service-role/AmazonEC2RoleforSSM',
+        ],
+    },
+}
+
+
+ASSUME_ROLE_POLICY_DOCUMENT = '''
+{
+  "Version": "2012-10-17",
+  "Statement": [
+    {
+      "Effect": "Allow",
+      "Principal": {
+        "Service": "ec2.amazonaws.com"
+      },
+      "Action": "sts:AssumeRole"
+    }
+  ]
+}
+'''.strip()
+
+
+IAM_INSTANCE_PROFILES = {
+    'ephemeral-ec2-1': {
+        'roles': [
+            'ephemeral-ec2-role-1',
+        ],
+    }
+}
+
+
+# User Data for Windows EC2 instance. Mainly used to set the password
+# and configure WinRM.
+# Inspired by the User Data script used by Packer
+# (from https://www.packer.io/intro/getting-started/build-image.html).
+WINDOWS_USER_DATA = '''
+<powershell>
+
+# TODO enable this once we figure out what is failing.
+#$ErrorActionPreference = "stop"
+
+# Set administrator password
+net user Administrator "%s"
+wmic useraccount where "name='Administrator'" set PasswordExpires=FALSE
+
+# First, make sure WinRM can't be connected to
+netsh advfirewall firewall set rule name="Windows Remote Management (HTTP-In)" new enable=yes action=block
+
+# Delete any existing WinRM listeners
+winrm delete winrm/config/listener?Address=*+Transport=HTTP  2>$Null
+winrm delete winrm/config/listener?Address=*+Transport=HTTPS 2>$Null
+
+# Create a new WinRM listener and configure
+winrm create winrm/config/listener?Address=*+Transport=HTTP
+winrm set winrm/config/winrs '@{MaxMemoryPerShellMB="0"}'
+winrm set winrm/config '@{MaxTimeoutms="7200000"}'
+winrm set winrm/config/service '@{AllowUnencrypted="true"}'
+winrm set winrm/config/service '@{MaxConcurrentOperationsPerUser="12000"}'
+winrm set winrm/config/service/auth '@{Basic="true"}'
+winrm set winrm/config/client/auth '@{Basic="true"}'
+
+# Configure UAC to allow privilege elevation in remote shells
+$Key = 'HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System'
+$Setting = 'LocalAccountTokenFilterPolicy'
+Set-ItemProperty -Path $Key -Name $Setting -Value 1 -Force
+
+# Configure and restart the WinRM Service; Enable the required firewall exception
+Stop-Service -Name WinRM
+Set-Service -Name WinRM -StartupType Automatic
+netsh advfirewall firewall set rule name="Windows Remote Management (HTTP-In)" new action=allow localip=any remoteip=any
+Start-Service -Name WinRM
+
+# Disable firewall on private network interfaces so prompts don't appear.
+Set-NetFirewallProfile -Name private -Enabled false
+</powershell>
+'''.lstrip()
+
+
+WINDOWS_BOOTSTRAP_POWERSHELL = '''
+Write-Output "installing PowerShell dependencies"
+Install-PackageProvider -Name NuGet -MinimumVersion 2.8.5.201 -Force
+Set-PSRepository -Name PSGallery -InstallationPolicy Trusted
+Install-Module -Name OpenSSHUtils -RequiredVersion 0.0.2.0
+
+Write-Output "installing OpenSSL server"
+Add-WindowsCapability -Online -Name OpenSSH.Server~~~~0.0.1.0
+# Various tools will attempt to use older versions of .NET. So we enable
+# the feature that provides them so it doesn't have to be auto-enabled
+# later.
+Write-Output "enabling .NET Framework feature"
+Install-WindowsFeature -Name Net-Framework-Core
+'''
+
+
+class AWSConnection:
+    """Manages the state of a connection with AWS."""
+
+    def __init__(self, automation, region: str):
+        self.automation = automation
+        self.local_state_path = automation.state_path
+
+        self.prefix = 'hg-'
+
+        self.session = boto3.session.Session(region_name=region)
+        self.ec2client = self.session.client('ec2')
+        self.ec2resource = self.session.resource('ec2')
+        self.iamclient = self.session.client('iam')
+        self.iamresource = self.session.resource('iam')
+
+        ensure_key_pairs(automation.state_path, self.ec2resource)
+
+        self.security_groups = ensure_security_groups(self.ec2resource)
+        ensure_iam_state(self.iamresource)
+
+    def key_pair_path_private(self, name):
+        """Path to a key pair private key file."""
+        return self.local_state_path / 'keys' / ('keypair-%s' % name)
+
+    def key_pair_path_public(self, name):
+        return self.local_state_path / 'keys' / ('keypair-%s.pub' % name)
+
+
+def rsa_key_fingerprint(p: pathlib.Path):
+    """Compute the fingerprint of an RSA private key."""
+
+    # TODO use rsa package.
+    res = subprocess.run(
+        ['openssl', 'pkcs8', '-in', str(p), '-nocrypt', '-topk8',
+         '-outform', 'DER'],
+        capture_output=True,
+        check=True)
+
+    sha1 = hashlib.sha1(res.stdout).hexdigest()
+    return ':'.join(a + b for a, b in zip(sha1[::2], sha1[1::2]))
+
+
+def ensure_key_pairs(state_path: pathlib.Path, ec2resource, prefix='hg-'):
+    remote_existing = {}
+
+    for kpi in ec2resource.key_pairs.all():
+        if kpi.name.startswith(prefix):
+            remote_existing[kpi.name[len(prefix):]] = kpi.key_fingerprint
+
+    # Validate that we have these keys locally.
+    key_path = state_path / 'keys'
+    key_path.mkdir(exist_ok=True, mode=0o700)
+
+    def remove_remote(name):
+        print('deleting key pair %s' % name)
+        key = ec2resource.KeyPair(name)
+        key.delete()
+
+    def remove_local(name):
+        pub_full = key_path / ('keypair-%s.pub' % name)
+        priv_full = key_path / ('keypair-%s' % name)
+
+        print('removing %s' % pub_full)
+        pub_full.unlink()
+        print('removing %s' % priv_full)
+        priv_full.unlink()
+
+    local_existing = {}
+
+    for f in sorted(os.listdir(key_path)):
+        if not f.startswith('keypair-') or not f.endswith('.pub'):
+            continue
+
+        name = f[len('keypair-'):-len('.pub')]
+
+        pub_full = key_path / f
+        priv_full = key_path / ('keypair-%s' % name)
+
+        with open(pub_full, 'r', encoding='ascii') as fh:
+            data = fh.read()
+
+        if not data.startswith('ssh-rsa '):
+            print('unexpected format for key pair file: %s; removing' %
+                  pub_full)
+            pub_full.unlink()
+            priv_full.unlink()
+            continue
+
+        local_existing[name] = rsa_key_fingerprint(priv_full)
+
+    for name in sorted(set(remote_existing) | set(local_existing)):
+        if name not in local_existing:
+            actual = '%s%s' % (prefix, name)
+            print('remote key %s does not exist locally' % name)
+            remove_remote(actual)
+            del remote_existing[name]
+
+        elif name not in remote_existing:
+            print('local key %s does not exist remotely' % name)
+            remove_local(name)
+            del local_existing[name]
+
+        elif remote_existing[name] != local_existing[name]:
+            print('key fingerprint mismatch for %s; '
+                  'removing from local and remote' % name)
+            remove_local(name)
+            remove_remote('%s%s' % (prefix, name))
+            del local_existing[name]
+            del remote_existing[name]
+
+    missing = KEY_PAIRS - set(remote_existing)
+
+    for name in sorted(missing):
+        actual = '%s%s' % (prefix, name)
+        print('creating key pair %s' % actual)
+
+        priv_full = key_path / ('keypair-%s' % name)
+        pub_full = key_path / ('keypair-%s.pub' % name)
+
+        kp = ec2resource.create_key_pair(KeyName=actual)
+
+        with priv_full.open('w', encoding='ascii') as fh:
+            fh.write(kp.key_material)
+            fh.write('\n')
+
+        priv_full.chmod(0o0600)
+
+        # SSH public key can be extracted via `ssh-keygen`.
+        with pub_full.open('w', encoding='ascii') as fh:
+            subprocess.run(
+                ['ssh-keygen', '-y', '-f', str(priv_full)],
+                stdout=fh,
+                check=True)
+
+        pub_full.chmod(0o0600)
+
+
+def delete_instance_profile(profile):
+    for role in profile.roles:
+        print('removing role %s from instance profile %s' % (role.name,
+                                                             profile.name))
+        profile.remove_role(RoleName=role.name)
+
+    print('deleting instance profile %s' % profile.name)
+    profile.delete()
+
+
+def ensure_iam_state(iamresource, prefix='hg-'):
+    """Ensure IAM state is in sync with our canonical definition."""
+
+    remote_profiles = {}
+
+    for profile in iamresource.instance_profiles.all():
+        if profile.name.startswith(prefix):
+            remote_profiles[profile.name[len(prefix):]] = profile
+
+    for name in sorted(set(remote_profiles) - set(IAM_INSTANCE_PROFILES)):
+        delete_instance_profile(remote_profiles[name])
+        del remote_profiles[name]
+
+    remote_roles = {}
+
+    for role in iamresource.roles.all():
+        if role.name.startswith(prefix):
+            remote_roles[role.name[len(prefix):]] = role
+
+    for name in sorted(set(remote_roles) - set(IAM_ROLES)):
+        role = remote_roles[name]
+
+        print('removing role %s' % role.name)
+        role.delete()
+        del remote_roles[name]
+
+    # We've purged remote state that doesn't belong. Create missing
+    # instance profiles and roles.
+    for name in sorted(set(IAM_INSTANCE_PROFILES) - set(remote_profiles)):
+        actual = '%s%s' % (prefix, name)
+        print('creating IAM instance profile %s' % actual)
+
+        profile = iamresource.create_instance_profile(
+            InstanceProfileName=actual)
+        remote_profiles[name] = profile
+
+    for name in sorted(set(IAM_ROLES) - set(remote_roles)):
+        entry = IAM_ROLES[name]
+
+        actual = '%s%s' % (prefix, name)
+        print('creating IAM role %s' % actual)
+
+        role = iamresource.create_role(
+            RoleName=actual,
+            Description=entry['description'],
+            AssumeRolePolicyDocument=ASSUME_ROLE_POLICY_DOCUMENT,
+        )
+
+        remote_roles[name] = role
+
+        for arn in entry['policy_arns']:
+            print('attaching policy %s to %s' % (arn, role.name))
+            role.attach_policy(PolicyArn=arn)
+
+    # Now reconcile state of profiles.
+    for name, meta in sorted(IAM_INSTANCE_PROFILES.items()):
+        profile = remote_profiles[name]
+        wanted = {'%s%s' % (prefix, role) for role in meta['roles']}
+        have = {role.name for role in profile.roles}
+
+        for role in sorted(have - wanted):
+            print('removing role %s from %s' % (role, profile.name))
+            profile.remove_role(RoleName=role)
+
+        for role in sorted(wanted - have):
+            print('adding role %s to %s' % (role, profile.name))
+            profile.add_role(RoleName=role)
+
+
+def find_windows_server_2019_image(ec2resource):
+    """Find the Amazon published Windows Server 2019 base image."""
+
+    images = ec2resource.images.filter(
+        Filters=[
+            {
+                'Name': 'owner-alias',
+                'Values': ['amazon'],
+            },
+            {
+                'Name': 'state',
+                'Values': ['available'],
+            },
+            {
+                'Name': 'image-type',
+                'Values': ['machine'],
+            },
+            {
+                'Name': 'name',
+                'Values': ['Windows_Server-2019-English-Full-Base-2019.02.13'],
+            },
+        ])
+
+    for image in images:
+        return image
+
+    raise Exception('unable to find Windows Server 2019 image')
+
+
+def ensure_security_groups(ec2resource, prefix='hg-'):
+    """Ensure all necessary Mercurial security groups are present.
+
+    All security groups are prefixed with ``hg-`` by default. Any security
+    groups having this prefix but aren't in our list are deleted.
+    """
+    existing = {}
+
+    for group in ec2resource.security_groups.all():
+        if group.group_name.startswith(prefix):
+            existing[group.group_name[len(prefix):]] = group
+
+    purge = set(existing) - set(SECURITY_GROUPS)
+
+    for name in sorted(purge):
+        group = existing[name]
+        print('removing legacy security group: %s' % group.group_name)
+        group.delete()
+
+    security_groups = {}
+
+    for name, group in sorted(SECURITY_GROUPS.items()):
+        if name in existing:
+            security_groups[name] = existing[name]
+            continue
+
+        actual = '%s%s' % (prefix, name)
+        print('adding security group %s' % actual)
+
+        group_res = ec2resource.create_security_group(
+            Description=group['description'],
+            GroupName=actual,
+        )
+
+        group_res.authorize_ingress(
+            IpPermissions=group['ingress'],
+        )
+
+        security_groups[name] = group_res
+
+    return security_groups
+
+
+def terminate_ec2_instances(ec2resource, prefix='hg-'):
+    """Terminate all EC2 instances managed by us."""
+    waiting = []
+
+    for instance in ec2resource.instances.all():
+        if instance.state['Name'] == 'terminated':
+            continue
+
+        for tag in instance.tags or []:
+            if tag['Key'] == 'Name' and tag['Value'].startswith(prefix):
+                print('terminating %s' % instance.id)
+                instance.terminate()
+                waiting.append(instance)
+
+    for instance in waiting:
+        instance.wait_until_terminated()
+
+
+def remove_resources(c, prefix='hg-'):
+    """Purge all of our resources in this EC2 region."""
+    ec2resource = c.ec2resource
+    iamresource = c.iamresource
+
+    terminate_ec2_instances(ec2resource, prefix=prefix)
+
+    for image in ec2resource.images.all():
+        if image.name.startswith(prefix):
+            remove_ami(ec2resource, image)
+
+    for group in ec2resource.security_groups.all():
+        if group.group_name.startswith(prefix):
+            print('removing security group %s' % group.group_name)
+            group.delete()
+
+    for profile in iamresource.instance_profiles.all():
+        if profile.name.startswith(prefix):
+            delete_instance_profile(profile)
+
+    for role in iamresource.roles.all():
+        if role.name.startswith(prefix):
+            print('removing role %s' % role.name)
+            role.delete()
+
+
+def wait_for_ip_addresses(instances):
+    """Wait for the public IP addresses of an iterable of instances."""
+    for instance in instances:
+        while True:
+            if not instance.public_ip_address:
+                time.sleep(2)
+                instance.reload()
+                continue
+
+            print('public IP address for %s: %s' % (
+                instance.id, instance.public_ip_address))
+            break
+
+
+def remove_ami(ec2resource, image):
+    """Remove an AMI and its underlying snapshots."""
+    snapshots = []
+
+    for device in image.block_device_mappings:
+        if 'Ebs' in device:
+            snapshots.append(ec2resource.Snapshot(device['Ebs']['SnapshotId']))
+
+    print('deregistering %s' % image.id)
+    image.deregister()
+
+    for snapshot in snapshots:
+        print('deleting snapshot %s' % snapshot.id)
+        snapshot.delete()
+
+
+def wait_for_ssm(ssmclient, instances):
+    """Wait for SSM to come online for an iterable of instance IDs."""
+    while True:
+        res = ssmclient.describe_instance_information(
+            Filters=[
+                {
+                    'Key': 'InstanceIds',
+                    'Values': [i.id for i in instances],
+                },
+            ],
+        )
+
+        available = len(res['InstanceInformationList'])
+        wanted = len(instances)
+
+        print('%d/%d instances available in SSM' % (available, wanted))
+
+        if available == wanted:
+            return
+
+        time.sleep(2)
+
+
+def run_ssm_command(ssmclient, instances, document_name, parameters):
+    """Run a PowerShell script on an EC2 instance."""
+
+    res = ssmclient.send_command(
+        InstanceIds=[i.id for i in instances],
+        DocumentName=document_name,
+        Parameters=parameters,
+        CloudWatchOutputConfig={
+            'CloudWatchOutputEnabled': True,
+        },
+    )
+
+    command_id = res['Command']['CommandId']
+
+    for instance in instances:
+        while True:
+            try:
+                res = ssmclient.get_command_invocation(
+                    CommandId=command_id,
+                    InstanceId=instance.id,
+                )
+            except botocore.exceptions.ClientError as e:
+                if e.response['Error']['Code'] == 'InvocationDoesNotExist':
+                    print('could not find SSM command invocation; waiting')
+                    time.sleep(1)
+                    continue
+                else:
+                    raise
+
+            if res['Status'] == 'Success':
+                break
+            elif res['Status'] in ('Pending', 'InProgress', 'Delayed'):
+                time.sleep(2)
+            else:
+                raise Exception('command failed on %s: %s' % (
+                    instance.id, res['Status']))
+
+
+ at contextlib.contextmanager
+def temporary_ec2_instances(ec2resource, config):
+    """Create temporary EC2 instances.
+
+    This is a proxy to ``ec2client.run_instances(**config)`` that takes care of
+    managing the lifecycle of the instances.
+
+    When the context manager exits, the instances are terminated.
+
+    The context manager evaluates to the list of data structures
+    describing each created instance. The instances may not be available
+    for work immediately: it is up to the caller to wait for the instance
+    to start responding.
+    """
+
+    ids = None
+
+    try:
+        res = ec2resource.create_instances(**config)
+
+        ids = [i.id for i in res]
+        print('started instances: %s' % ' '.join(ids))
+
+        yield res
+    finally:
+        if ids:
+            print('terminating instances: %s' % ' '.join(ids))
+            for instance in res:
+                instance.terminate()
+            print('terminated %d instances' % len(ids))
+
+
+ at contextlib.contextmanager
+def create_temp_windows_ec2_instances(c: AWSConnection, config):
+    """Create temporary Windows EC2 instances.
+
+    This is a higher-level wrapper around ``create_temp_ec2_instances()`` that
+    configures the Windows instance for Windows Remote Management. The emitted
+    instances will have a ``winrm_client`` attribute containing a
+    ``pypsrp.client.Client`` instance bound to the instance.
+    """
+    if 'IamInstanceProfile' in config:
+        raise ValueError('IamInstanceProfile cannot be provided in config')
+    if 'UserData' in config:
+        raise ValueError('UserData cannot be provided in config')
+
+    password = c.automation.default_password()
+
+    config = copy.deepcopy(config)
+    config['IamInstanceProfile'] = {
+        'Name': 'hg-ephemeral-ec2-1',
+    }
+    config.setdefault('TagSpecifications', []).append({
+        'ResourceType': 'instance',
+        'Tags': [{'Key': 'Name', 'Value': 'hg-temp-windows'}],
+    })
+    config['UserData'] = WINDOWS_USER_DATA % password
+
+    with temporary_ec2_instances(c.ec2resource, config) as instances:
+        wait_for_ip_addresses(instances)
+
+        print('waiting for Windows Remote Management service...')
+
+        for instance in instances:
+            client = wait_for_winrm(instance.public_ip_address, 'Administrator', password)
+            print('established WinRM connection to %s' % instance.id)
+            instance.winrm_client = client
+
+        yield instances
+
+
+def ensure_windows_dev_ami(c: AWSConnection, prefix='hg-'):
+    """Ensure Windows Development AMI is available and up-to-date.
+
+    If necessary, a modern AMI will be built by starting a temporary EC2
+    instance and bootstrapping it.
+
+    Obsolete AMIs will be deleted so there is only a single AMI having the
+    desired name.
+
+    Returns an ``ec2.Image`` of either an existing AMI or a newly-built
+    one.
+    """
+    ec2client = c.ec2client
+    ec2resource = c.ec2resource
+    ssmclient = c.session.client('ssm')
+
+    name = '%s%s' % (prefix, 'windows-dev')
+
+    config = {
+        'BlockDeviceMappings': [
+            {
+                'DeviceName': '/dev/sda1',
+                'Ebs': {
+                    'DeleteOnTermination': True,
+                    'VolumeSize': 32,
+                    'VolumeType': 'gp2',
+                },
+            }
+        ],
+        'ImageId': find_windows_server_2019_image(ec2resource).id,
+        'InstanceInitiatedShutdownBehavior': 'stop',
+        'InstanceType': 't3.medium',
+        'KeyName': '%sautomation' % prefix,
+        'MaxCount': 1,
+        'MinCount': 1,
+        'SecurityGroupIds': [c.security_groups['windows-dev-1'].id],
+    }
+
+    commands = [
+        # Need to start the service so sshd_config is generated.
+        'Start-Service sshd',
+        'Write-Output "modifying sshd_config"',
+        r'$content = Get-Content C:\ProgramData\ssh\sshd_config',
+        '$content = $content -replace "Match Group administrators","" -replace "AuthorizedKeysFile __PROGRAMDATA__/ssh/administrators_authorized_keys",""',
+        r'$content | Set-Content C:\ProgramData\ssh\sshd_config',
+        'Import-Module OpenSSHUtils',
+        r'Repair-SshdConfigPermission C:\ProgramData\ssh\sshd_config -Confirm:$false',
+        'Restart-Service sshd',
+        'Write-Output "installing OpenSSL client"',
+        'Add-WindowsCapability -Online -Name OpenSSH.Client~~~~0.0.1.0',
+        'Set-Service -Name sshd -StartupType "Automatic"',
+        'Write-Output "OpenSSH server running"',
+    ]
+
+    with INSTALL_WINDOWS_DEPENDENCIES.open('r', encoding='utf-8') as fh:
+        commands.extend(l.rstrip() for l in fh)
+
+    # Disable Windows Defender when bootstrapping because it just slows
+    # things down.
+    commands.insert(0, 'Set-MpPreference -DisableRealtimeMonitoring $true')
+    commands.append('Set-MpPreference -DisableRealtimeMonitoring $false')
+
+    # Compute a deterministic fingerprint to determine whether image needs
+    # to be regenerated.
+    fingerprint = {
+        'instance_config': config,
+        'user_data': WINDOWS_USER_DATA,
+        'initial_bootstrap': WINDOWS_BOOTSTRAP_POWERSHELL,
+        'bootstrap_commands': commands,
+    }
+
+    fingerprint = json.dumps(fingerprint, sort_keys=True)
+    fingerprint = hashlib.sha256(fingerprint.encode('utf-8')).hexdigest()
+
+    # Find existing AMIs with this name and delete the ones that are invalid.
+    # Store a reference to a good image so it can be returned one the
+    # image state is reconciled.
+    images = ec2resource.images.filter(
+        Filters=[{'Name': 'name', 'Values': [name]}])
+
+    existing_image = None
+
+    for image in images:
+        if image.tags is None:
+            print('image %s for %s lacks required tags; removing' % (
+                image.id, image.name))
+            remove_ami(ec2resource, image)
+        else:
+            tags = {t['Key']: t['Value'] for t in image.tags}
+
+            if tags.get('HGIMAGEFINGERPRINT') == fingerprint:
+                existing_image = image
+            else:
+                print('image %s for %s has wrong fingerprint; removing' % (
+                      image.id, image.name))
+                remove_ami(ec2resource, image)
+
+    if existing_image:
+        return existing_image
+
+    print('no suitable Windows development image found; creating one...')
+
+    with create_temp_windows_ec2_instances(c, config) as instances:
+        assert len(instances) == 1
+        instance = instances[0]
+
+        wait_for_ssm(ssmclient, [instance])
+
+        # On first boot, install various Windows updates.
+        # We would ideally use PowerShell Remoting for this. However, there are
+        # trust issues that make it difficult to invoke Windows Update
+        # remotely. So we use SSM, which has a mechanism for running Windows
+        # Update.
+        print('installing Windows features...')
+        run_ssm_command(
+            ssmclient,
+            [instance],
+            'AWS-RunPowerShellScript',
+            {
+                'commands': WINDOWS_BOOTSTRAP_POWERSHELL.split('\n'),
+            },
+        )
+
+        # Reboot so all updates are fully applied.
+        print('rebooting instance %s' % instance.id)
+        ec2client.reboot_instances(InstanceIds=[instance.id])
+
+        time.sleep(15)
+
+        print('waiting for Windows Remote Management to come back...')
+        client = wait_for_winrm(instance.public_ip_address, 'Administrator',
+                                c.automation.default_password())
+        print('established WinRM connection to %s' % instance.id)
+        instance.winrm_client = client
+
+        print('bootstrapping instance...')
+        run_powershell(instance.winrm_client, '\n'.join(commands))
+
+        print('bootstrap completed; stopping %s to create image' % instance.id)
+        instance.stop()
+
+        ec2client.get_waiter('instance_stopped').wait(
+            InstanceIds=[instance.id],
+            WaiterConfig={
+                'Delay': 5,
+            })
+        print('%s is stopped' % instance.id)
+
+        image = instance.create_image(
+            Name=name,
+            Description='Mercurial Windows development environment',
+        )
+
+        image.create_tags(Tags=[
+            {
+                'Key': 'HGIMAGEFINGERPRINT',
+                'Value': fingerprint,
+            },
+        ])
+
+        print('waiting for image %s' % image.id)
+
+        ec2client.get_waiter('image_available').wait(
+            ImageIds=[image.id],
+        )
+
+        print('image %s available as %s' % (image.id, image.name))
+
+        return image
+
+
+ at contextlib.contextmanager
+def temporary_windows_dev_instances(c: AWSConnection, image, instance_type,
+                                    prefix='hg-', disable_antivirus=False):
+    """Create a temporary Windows development EC2 instance.
+
+    Context manager resolves to the list of ``EC2.Instance`` that were created.
+    """
+    config = {
+        'BlockDeviceMappings': [
+            {
+                'DeviceName': '/dev/sda1',
+                'Ebs': {
+                    'DeleteOnTermination': True,
+                    'VolumeSize': 32,
+                    'VolumeType': 'gp2',
+                },
+            }
+        ],
+        'ImageId': image.id,
+        'InstanceInitiatedShutdownBehavior': 'stop',
+        'InstanceType': instance_type,
+        'KeyName': '%sautomation' % prefix,
+        'MaxCount': 1,
+        'MinCount': 1,
+        'SecurityGroupIds': [c.security_groups['windows-dev-1'].id],
+    }
+
+    with create_temp_windows_ec2_instances(c, config) as instances:
+        if disable_antivirus:
+            for instance in instances:
+                run_powershell(
+                    instance.winrm_client,
+                    'Set-MpPreference -DisableRealtimeMonitoring $true')
+
+        yield instances
diff --git a/contrib/automation/hgautomation/__init__.py b/contrib/automation/hgautomation/__init__.py
new file mode 100644
--- /dev/null
+++ b/contrib/automation/hgautomation/__init__.py
@@ -0,0 +1,59 @@
+# __init__.py - High-level automation interfaces
+#
+# Copyright 2019 Gregory Szorc <gregory.szorc at gmail.com>
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+
+# no-check-code because Python 3 native.
+
+import pathlib
+import secrets
+
+from .aws import (
+    AWSConnection,
+)
+
+
+class HGAutomation:
+    """High-level interface for Mercurial automation.
+
+    Holds global state, provides access to other primitives, etc.
+    """
+
+    def __init__(self, state_path: pathlib.Path):
+        self.state_path = state_path
+
+        state_path.mkdir(exist_ok=True)
+
+    def default_password(self):
+        """Obtain the default password to use for remote machines.
+
+        A new password will be generated if one is not stored.
+        """
+        p = self.state_path / 'default-password'
+
+        try:
+            with p.open('r', encoding='ascii') as fh:
+                data = fh.read().strip()
+
+                if data:
+                    return data
+
+        except FileNotFoundError:
+            pass
+
+        password = secrets.token_urlsafe(24)
+
+        with p.open('w', encoding='ascii') as fh:
+            fh.write(password)
+            fh.write('\n')
+
+        p.chmod(0o0600)
+
+        return password
+
+    def aws_connection(self, region: str):
+        """Obtain an AWSConnection instance bound to a specific region."""
+
+        return AWSConnection(self, region)
diff --git a/contrib/automation/automation.py b/contrib/automation/automation.py
new file mode 100755
--- /dev/null
+++ b/contrib/automation/automation.py
@@ -0,0 +1,70 @@
+#!/usr/bin/env python3
+#
+# automation.py - Perform tasks on remote machines
+#
+# Copyright 2019 Gregory Szorc <gregory.szorc at gmail.com>
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+
+import os
+import pathlib
+import subprocess
+import sys
+import venv
+
+
+HERE = pathlib.Path(os.path.abspath(__file__)).parent
+REQUIREMENTS_TXT = HERE / 'requirements.txt'
+SOURCE_DIR = HERE.parent.parent
+VENV = SOURCE_DIR / 'build' / 'venv-automation'
+
+
+def bootstrap():
+    venv_created = not VENV.exists()
+
+    VENV.parent.mkdir(exist_ok=True)
+
+    venv.create(VENV, with_pip=True)
+
+    if os.name == 'nt':
+        venv_bin = VENV / 'Scripts'
+        pip = venv_bin / 'pip.exe'
+        python = venv_bin / 'python.exe'
+    else:
+        venv_bin = VENV / 'bin'
+        pip = venv_bin / 'pip'
+        python = venv_bin / 'python'
+
+    args = [str(pip), 'install', '-r', str(REQUIREMENTS_TXT),
+            '--disable-pip-version-check']
+
+    if not venv_created:
+        args.append('-q')
+
+    subprocess.run(args, check=True)
+
+    os.environ['HGAUTOMATION_BOOTSTRAPPED'] = '1'
+    os.environ['PATH'] = '%s%s%s' % (
+        venv_bin, os.pathsep, os.environ['PATH'])
+
+    subprocess.run([str(python), __file__] + sys.argv[1:], check=True)
+
+
+def run():
+    import hgautomation.cli as cli
+
+    # Need to strip off main Python executable.
+    cli.main()
+
+
+if __name__ == '__main__':
+    try:
+        if 'HGAUTOMATION_BOOTSTRAPPED' not in os.environ:
+            bootstrap()
+        else:
+            run()
+    except subprocess.CalledProcessError as e:
+        sys.exit(e.returncode)
+    except KeyboardInterrupt:
+        sys.exit(1)
diff --git a/contrib/automation/README.rst b/contrib/automation/README.rst
new file mode 100644
--- /dev/null
+++ b/contrib/automation/README.rst
@@ -0,0 +1,127 @@
+====================
+Mercurial Automation
+====================
+
+This directory contains code and utilities for building and testing Mercurial
+on remote machines.
+
+The ``automation.py`` Script
+============================
+
+``automation.py`` is an executable Python script (requires Python 3.5+)
+that serves as a driver to common automation tasks.
+
+When executed, the script will *bootstrap* a virtualenv in
+``<source-root>/build/venv-automation`` then re-execute itself using
+that virtualenv. So there is no need for the caller to have a virtualenv
+explicitly activated. This virtualenv will be populated with various
+dependencies (as defined by the ``requirements.txt`` file).
+
+To see what you can do with this script, simply run it::
+
+   $ ./automation.py
+
+Local State
+===========
+
+By default, local state required to interact with remote servers is stored
+in the ``~/.hgautomation`` directory.
+
+We attempt to limit persistent state to this directory. Even when
+performing tasks that may have side-effects, we try to limit those
+side-effects so they don't impact the local system. e.g. when we SSH
+into a remote machine, we create a temporary directory for the SSH
+config so the user's known hosts file isn't updated.
+
+AWS Integration
+===============
+
+Various automation tasks integrate with AWS to provide access to
+resources such as EC2 instances for generic compute.
+
+This obviously requires an AWS account and credentials to work.
+
+We use the ``boto3`` library for interacting with AWS APIs. We do not employ
+any special functionality for telling ``boto3`` where to find AWS credentials. See
+https://boto3.amazonaws.com/v1/documentation/api/latest/guide/configuration.html
+for how ``boto3`` works. Once you have configured your environment such
+that ``boto3`` can find credentials, interaction with AWS should *just work*.
+
+.. hint::
+
+   Typically you have a ``~/.aws/credentials`` file containing AWS
+   credentials. If you manage multiple credentials, you can override which
+   *profile* to use at run-time by setting the ``AWS_PROFILE`` environment
+   variable.
+
+Resource Management
+-------------------
+
+Depending on the task being performed, various AWS services will be accessed.
+This of course requires AWS credentials with permissions to access these
+services.
+
+The following AWS services can be accessed by automation tasks:
+
+* EC2
+* IAM
+* Simple Systems Manager (SSM)
+
+Various resources will also be created as part of performing various tasks.
+This also requires various permissions.
+
+The following AWS resources can be created by automation tasks:
+
+* EC2 key pairs
+* EC2 security groups
+* EC2 instances
+* IAM roles and instance profiles
+* SSM command invocations
+
+When possible, we prefix resource names with ``hg-`` so they can easily
+be identified as belonging to Mercurial.
+
+.. important::
+
+   We currently assume that AWS accounts utilized by *us* are single
+   tenancy. Attempts to have discrete users of ``automation.py`` (including
+   sharing credentials across machines) using the same AWS account can result
+   in them interfering with each other and things breaking.
+
+Cost of Operation
+-----------------
+
+``automation.py`` tries to be frugal with regards to utilization of remote
+resources. Persistent remote resources are minimized in order to keep costs
+in check. For example, EC2 instances are often ephemeral and only live as long
+as the operation being performed.
+
+Under normal operation, recurring costs are limited to:
+
+* Storage costs for AMI / EBS snapshots. This should be just a few pennies
+  per month.
+
+When running EC2 instances, you'll be billed accordingly. By default, we
+use *small* instances, like ``t3.medium``. This instance type costs ~$0.07 per
+hour.
+
+.. note::
+
+   When running Windows EC2 instances, AWS bills at the full hourly cost, even
+   if the instance doesn't run for a full hour (per-second billing doesn't
+   apply to Windows AMIs).
+
+Managing Remote Resources
+-------------------------
+
+Occassionally, there may be an error purging a temporary resource. Or you
+may wish to forcefully purge remote state. Commands can be invoked to manually
+purge remote resources.
+
+To terminate all EC2 instances that we manage::
+
+   $ automation.py terminate-ec2-instances
+
+To purge all EC2 resources that we manage::
+
+   $ automation.py purge-ec2-resources



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