github-deploy-agent

The github-deploy-agent is a simple go agent that periodically polls the github api and checks for new deployments. If found, it executes a hook to deploy.

Workflow

In my case I use wercker to create a deployment object in the repository.

On startup the agent looks for the latest deployment object, and deploys it, if no success message has been created yet.

The agent then periodically polls the repository and grabs the latest deployment. If it is newer than the previously deployed one, it starts deploying the new one.

• It creates a deployment status pending.

• A pre_task is fired, if available.

• If tries executing a file called ./hooks/$task, where $task is the string from the deployment object. This allows for different actions to be taken.

  The hook gets passed a number of environment variables (see below) which define which branch/commit of the repository should be committed.

  This hook, which can be anything (bash scripts, binaries etc.) can now perform the actual deploy.

• A post_success hook is fired on success with the same environment variables, a post_failure otherwise. Errors here are ignored.

  This can be used for slack notifications etc.

• The agent creates a success status if the exit code is 0, failure otherwise. If the task didn't exist as a hook, an error status is raised.

• The agent sleeps for --sleep before checking for the next deployment again.

Environment Variables

All hooks are passed the same environment variables.

Name	Desc
GITHUB_TASK	The task name
GITHUB_DEPLOYMENT_ID	ID of the deployment
GITHUB_DEPLOYMENT_URL	URL of the deployment object in the Github API
GITHUB_REF	Branch name to be deployed
GITHUB_SHA	SHA of the commit to be deployed
GITHUB_OWNER	Owner of the repository
GITHUB_REPO	Repository name
GITHUB_CREATOR	Name of the user that created the deployment
GITHUB_CREATOR_AVATAR	Avatar URL of the creator
GITHUB_ENV	The env the agent is listening on

Caveats

1. If multiple deployments are created for the same environment while the agent sleeps, only the latest is acted upon. If the deployments differ e.g. in the tasks to execute, this may lead to unexpected / confusing behavior.

2. Although the agent is single threaded (and thus only applies one deploy at a time), it does not help you with downtime-free rollouts etc.

Future Improvements

• Github Deployment API supports a payload. This is currently not made available to the hook.
• Expose the output of the hooks, e.g. by uploading them to Gist.