Allow running marge-bot as a single CLI job (#289)

README.md

@@ -133,6 +133,9 @@ optional arguments:
                            [env var: MARGE_SOURCE_BRANCH_REGEXP] (default: .*)
   --debug               Debug logging (includes all HTTP requests etc).
                            [env var: MARGE_DEBUG] (default: False)
+  --cli                 Run marge-bot as a single CLI command, not as a long-running service.
+                        This may be used to run marge-bot in scheduled CI pipelines or cronjobs.
+                           [env var: MARGE_CLI] (default: False)
 ```
 Here is a config file example
 ```yaml
@@ -299,6 +302,43 @@ configs:
     name: marge_bot_config
 ```
 
+### Running marge-bot in CI
+
+You can also run marge-bot directly in your existing CI via scheduled pipelines
+if you'd like to avoid setting up any additional infrastructure.
+
+This way, you can inject secrets for marge-bot's credentials at runtime
+inside the ephemeral container for each run by adding them to protected CI/CD
+variables in a dedicated marge-bot runner project, as well as store execution
+logs as artifacts for evidence.
+
+You can also configure multiple setups in different CI schedules by supplying
+`MARGE_*` environment variables per-schedule, such as running a different set
+of projects or settings at different times.
+
+Note that in this case, marge-bot will be slower than when run as a service,
+depending on the frequency of your pipeline schedules.
+
+Create a marge-bot runner project, and add the variables `MARGE_AUTH_TOKEN`
+(of type Variable) and `MARGE_SSH_KEY_FILE` (of type File) in your CI/CD
+Variables settings.
+
+Then add a scheduled pipeline run to your project with the following minimal
+`.gitlab-ci.yml` config:
+
+```yaml
+run:
+  image:
+    name: smarkets/marge-bot:latest
+    entrypoint: [""]
+  only:
+    - schedules
+  variables:
+    MARGE_CLI: "true"
+    MARGE_GITLAB_URL: "$CI_SERVER_URL"
+  script: marge.app
+```
+
 ### Running marge-bot as a plain python app
 
 #### Installing marge-bot with nix

marge/app.py

@@ -224,6 +224,11 @@ def regexp(str_regex):
         action='store_true',
         help='Skip CI when updating individual MRs when using batches'
     )
+    parser.add_argument(
+        '--cli',
+        action='store_true',
+        help='Run marge-bot as a single CLI command, not a service'
+    )
     config = parser.parse_args(args)
 
     if config.use_merge_strategy and config.batch:
@@ -327,6 +332,7 @@ def main(args=None):
                 skip_ci_batches=options.skip_ci_batches,
             ),
             batch=options.batch,
+            cli=options.cli,
         )
 
         marge_bot = bot.Bot(api=api, config=config)

marge/bot.py

@@ -59,6 +59,9 @@ def _run(self, repo_manager):
                 time_to_sleep_between_projects_in_secs,
                 projects,
             )
+            if self._config.cli:
+                return
+
             big_sleep = max(0,
                             min_time_to_sleep_after_iterating_all_projects_in_secs -
                             time_to_sleep_between_projects_in_secs * len(projects))
@@ -187,7 +190,7 @@ def _get_single_job(self, project, merge_request, repo, options):
 
 class BotConfig(namedtuple('BotConfig',
                            'user ssh_key_file project_regexp merge_order merge_opts git_timeout ' +
-                           'git_reference_repo branch_regexp source_branch_regexp batch')):
+                           'git_reference_repo branch_regexp source_branch_regexp batch cli')):
     pass