runner/docs/adrs/0361-wrapper-action.md

ADR 361: Wrapper Action

Date: 2020-03-06

Status: Pending

Context

In addition to action's regular execution, action author may wants their action has a chance to participate in:

• Job initialize
  My Action will collect machine resource usage (CPU/RAM/Disk) during a workflow job execution, we need to start perf recorder at the begin of the job.
• Job cleanup
  My Action will dirty local workspace or machine environment during execution, we need to cleanup these changes at the end of the job.
  Ex: actions/checkout@v2 will write github.token into local .git/config during execution, it has post job cleanup defined to undo the changes.

Decision

Add pre and post execution to action

Node Action Example:

 name: 'My action with pre'
 description: 'My action with pre'
 runs:
   using: 'node12'
   pre: 'setup.js'
   pre-if: 'success()' // Optional
   main: 'index.js'
   post: 'cleanup.js'
   post-if: 'success()' // Optional

Container Action Example:

 name: 'My action with pre'
 description: 'My action with pre'
 runs:
   using: 'docker'
   image: 'mycontainer:latest'
   pre-entrypoint: 'setup.sh'
   pre-if: 'success()' // Optional
   entrypoint: 'entrypoint.sh'
   post-entrypoint: 'cleanup.sh'
   post-if: 'success()' // Optional

Both pre and post will has default pre-if/post-if sets to always().
Setting pre to always() will make sure no matter what condition evaluate result the main gets at runtime, the pre has always run already.
pre executes in order of how the steps are defined.
pre will always be added to job steps list during job setup.

Action referenced from local repository (./my-action) won't get pre setup correctly since the repository haven't checkout during job initialize.
We can't use GitHub api to download the repository since there is a about 3 mins delay between git push and the new commit available to download using GitHub api.

post will be pushed into a poststeps stack lazily when the action's pre or main execution passed if condition check and about to run, you can't have an action that only contains a post, we will pop and run each post after all pre and main finished.

Currently post works for both repository action (org/repo@v1) and local action (./my-action)

Valid action:

• only has main
• has pre and main
• has main and post
• has pre, main and post

Invalid action:

• only has pre
• only has post
• has pre and post

Potential downside of introducing pre:

• Extra magic wrt step order. Users should control the step order. Especially when we introduce templates.
• Eliminates the possibility to lazily download the action tarball, since pre always run by default, we have to download the tarball to check whether action defined a pre
• pre doesn't work with local action, we suggested customer use local action for testing their action changes, ex CI for their action, to avoid delay between git push and GitHub repo tarball download api.
• Condition on the pre can't be controlled using dynamic step outputs. pre executes too early.