Add an executor for Docker on Windows Server 2016

windows-docker/README.md

+# GitLab Runner Custom Executor for Docker on Windows Server 2016
+
+## Overview
+
+This Python script allows GitLab CI jobs to be run inside Docker
+containers on Windows Server 2016, which is [not supported][1] by the
+native Docker executor included in GitLab Runner.
+
+## Prerequisites
+
+- [GitLab Runner][2]
+- [Docker][3]
+- [Python 3.6+][4]
+
+## Installation
+
+- Register a new GitLab CI runner using `gitlab-runner.exe register`,
+  specifying `custom` as the executor to use.
+
+- Adjust the relevant section of GitLab Runner's `config.toml` so
+  that the executor gets invoked properly:
+
+  ```toml
+  shell = "powershell"
+  [runners.custom]
+    config_exec = "C:\\path\\to\\python\\python.exe"
+    config_args = [ "C:\\path\\to\\windows-docker\\executor.py", "config" ]
+    prepare_exec = "C:\\path\\to\\python\\python.exe"
+    prepare_args = [ "C:\\path\\to\\windows-docker\\executor.py", "prepare" ]
+    run_exec = "C:\\path\\to\\python\\python.exe"
+    run_args = [ "C:\\path\\to\\windows-docker\\executor.py", "run" ]
+    cleanup_exec = "C:\\path\\to\\python\\python.exe"
+    cleanup_args = [ "C:\\path\\to\\windows-docker\\executor.py", "cleanup" ]
+  ```
+
+## Limitations
+
+- Docker images are *not* automatically pulled or updated to the latest
+  available version during job setup.  `docker pull` needs to be either
+  run manually or from the Windows Task Scheduler.
+
+[1]: https://docs.gitlab.com/runner/executors/docker.html#supported-windows-versions
+[2]: https://docs.gitlab.com/runner/install/windows.html
+[3]: https://docs.microsoft.com/en-us/virtualization/windowscontainers/quick-start/set-up-environment
+[4]: https://www.python.org/downloads/windows/

windows-docker/executor.py

+"""
+executor.py - GitLab Runner Custom executor script for Docker on Windows
+
+Written in 2020 by Michał Kępień <michal@isc.org>
+
+To the extent possible under law, the author(s) have dedicated all copyright
+and related and neighboring rights to this software to the public domain
+worldwide.  This software is distributed without any warranty.
+
+You should have received a copy of the CC0 Public Domain Dedication along with
+this software.  If not, see http://creativecommons.org/publicdomain/zero/1.0/.
+"""
+
+import json
+import os
+import subprocess
+import sys
+
+
+DOCKER_PATH = 'C:\\Program Files\\Docker\\docker.exe'
+
+
+def fatal_error(message):
+    """
+    Print an error message to stderr and exit.
+    """
+    print(message, file=sys.stderr)
+    sys.exit(1)
+
+
+def docker_command(cmd):
+    """
+    Invoke the given Docker command, exiting immediately if it fails.
+    """
+    try:
+        subprocess.run([DOCKER_PATH] + cmd, check=True)
+    except subprocess.CalledProcessError:
+        sys.exit(1)
+
+
+def do_config(*_):
+    """
+    Perform the Config stage of a GitLab CI job.
+    """
+    config = {
+        'builds_dir': 'C:\\builds',
+        'cache_dir': 'C:\\cache',
+        'builds_dir_is_shared': False,
+    }
+    print(json.dumps(config))
+
+
+def do_prepare(container_name, _):
+    """
+    Perform the Prepare stage of a GitLab CI job.
+    """
+    docker_command(['run',
+                    '--name', container_name,
+                    '--interactive',
+                    '--detach',
+                    '--rm',
+                    os.environ['CUSTOM_ENV_CI_JOB_IMAGE']])
+
+
+def do_run(container_name, args):
+    """
+    Perform the Run stage of a GitLab CI job.
+    """
+    valid_stages = [
+        'prepare_script',
+        'get_sources',
+        'restore_cache',
+        'download_artifacts',
+        'build_script',
+        'step_script',
+        'after_script',
+        'archive_cache',
+        'upload_artifacts_on_success',
+        'upload_artifacts_on_failure',
+    ]
+
+    script_src = args[0]
+    stage = args[1]
+
+    if stage not in valid_stages:
+        fatal_error(f'Unsupported run stage "{stage}"')
+
+    script_dst_path = f'C:\\{stage}.ps1'
+    script_dst = f'{container_name}:{script_dst_path}'
+    docker_command(['cp', script_src, script_dst])
+    docker_command(['exec', container_name, 'powershell.exe', script_dst_path])
+
+
+def do_cleanup(container_name, _):
+    """
+    Perform the Cleanup stage of a GitLab CI job.
+    """
+    docker_command(['stop', container_name])
+
+
+def main():
+    """
+    Parse arguments and perform the requested stage of a GitLab CI job.
+    """
+    actions = {
+        'config': do_config,
+        'prepare': do_prepare,
+        'run': do_run,
+        'cleanup': do_cleanup,
+    }
+    valid_actions = '|'.join(actions.keys())
+
+    try:
+        action = actions[sys.argv[1]]
+    except (IndexError, KeyError):
+        fatal_error(f'Usage: {sys.argv[0]} {valid_actions} [args...]')
+
+    container_name = 'gitlab-runner-' + os.environ['CUSTOM_ENV_CI_JOB_ID']
+    action(container_name, sys.argv[2:])
+
+
+if __name__ == '__main__':
+    main()