Marathon deployment tool

Set up

Development

• Requires Python 3.7 or higher
• Dependencies in requirements.txt: pip3 install -r requirements.txt
• Use of virtualenv is recommended as always
• For testing against a local cluster you may use mesos-mini

Options

• --marathon: Marathon to connect to. Supports comma-separated hosts: http://m1:8080,http://m2:8080,http://m3:8080. Defaults to http://localhost:8080.
• --appid: Application ID of the app to be affected. Example: /group1/foo/bar
• --put: May be two values:
  • Path to a single, .json file, containing the definition of a single Marathon application
  • Path to a folder containing a set .json files, each with the definition of a single Marathon application. No recursivity supported. Files starting with '#' are ignored.
  • If the .json refers to a pre-existing application, it will be updated
  • If the application is to be updated, a backup json will be created (in ./backups/{appid}_{date}.json; backups folder will be created if it does not exist)
• --fullrollback: If present, the --put parameter is set to a folder, and a rollback is performed (read 'Rolling back' below), all previously created/updated apps are rolled back (if updated) or destroyed (if created) in reverse order (last updated/created will be the first to be rolled back/destroyed). If the initial rollback is forced, this 'full rollback' is not performed.
• --tag: Only update the Docker tag of a given --appid. As such, only Docker applications are supported.
• --restart: Restart an application. It's done in rolling fashion: New instances are created, then old ones taken down. No downtime, but requires enough resources in the cluster to fit instances_amount * 2 during deployment
• --inplacerestart: Scale down and back up an application. Tough way to do a restart: Implies downtime, but has lower resources requirements.
• --scale: Scale up/down an application.
• --instances: Get the amount of instances an application has.
• --list: List all applications in the Marathon cluster and their Docker images/tags
• --saveapp: [Not implemented] Save a given application's json
• --dumpall: [Not implemented] Save all applications' jsons

Rolling back

Most operations on Marathon imply a 'Deployment'. Whether is the creation, update, destruction, or restart of an app.

In most cases (except on creation, for now) these deployments can be cancelled (Ctrl+C while waiting for it to finish). When cancelling a deployment, a new deployment is created (the one to roll back to the previous state).

When cancelling a deployment, an option is given: To let it flow (the new rollback-deployment is created) or to force the cancellation (the deployment is killed, and the affected app is left as-is; this is dangerous and the application must be manually controlled afterwards).
If the cancellation is not forced, in turn, this 'rollback-deployment' cannot be cancelled: they are triggered and are not waited for completion, we just move on.

When using the --fullrollback parameter, upon forcefully cancelling a deployment (triggered by a .json read from the folder given with the --put parameter), the rest of the applications are not rolled back. The script just exits and a manual rollback must be performed (the backup jsons may come in handy here).
If you do not force the cancellation (let the rollback deployment flow), the rest of the applications will be rolled back, in the inverse order they were created/updated.

Rollback workflow

Release new version

To release a new version, with a valid ~/.pypirc configured for authentication:

1. Have Twine installed: pip install twine
2. Edit the version number in marathon_deploy/version.py
3. Run python setup.py sdist to build a new package
4. (Optional) Install it locally using pip install dist/marathon-deploy-$(cat marathon_deploy/version.py).tar.gz
5. Run twine upload dist/*
6. Make the appropiate changes to the CHANGELOG.md
7. Commit the new version to Git: git add CHANGELOG.MD marathon_deploy/version.py && git commit -am "Version $(cat marathon_deploy/version.py)" && git tag $(cat marathon_deploy/version.py) && git push --tags

TODO

• Verify if the target app is a Docker container when using --tag
• Support cancellation of the creation of an app
• Assume yes (unattended)
• On failed deployment, show last task failure message (stderr)
• BUG: --list blows up when there are non-Docker apps in Marathon
• BUG: Ordering is broken with 10> apps (ordering as string, so, for example, 19 goes before 2)
• App deletion