Getting a Github Action to run randomly

If you have a Github Action set on a cron schedule, but don’t necessarily want it to always run on that schedule - for example a daily cron that doesn’t always need to run daily - it’s possible to introduce a random cancellation step.

In the first step, set an environment variable. Here we’re using $((RANDOM%2)) to give a 50% chance. This sets a 1 or 0 value against the $PROCEED environment variable.

steps:
- id: Roll dice
  run: echo "PROCEED=$((RANDOM%2))" >> $GITHUB_ENV
  shell: bash

Next, call the cancel action but only if $PROCEED was set to 0 in the previous step.

- if: env.PROCEED == '0'
  name: Cancelling
  uses: andymckay/cancel-[email protected]

The cancellation call can take about 15-30 seconds, so it’s worth adding in a sleep step so that the actual remaining build steps don’t get called and killed halfway.

- if: env.PROCEED == '0'
  name: Waiting for cancellation
  run: sleep 60

All together, a snippet of a sample workflow:

Here’s an example workflow which runs daily at 5:30, but now should run just half the time.

name: My Action

# Controls when the action will run. Triggers the workflow on push or pull request
# events but only for the master branch
on:
  push:
    branches: [ master ]
  schedule:
    - cron:  '30 5 * * *'
    
    

# A workflow run is made up of one or more jobs that can run sequentially or in parallel
jobs:
  # This workflow contains a single job called "build"
  build:
    
    # The type of runner that the job will run on
    runs-on: ubuntu-latest

    # Steps represent a sequence of tasks that will be executed as part of the job
    steps:
    - id: Roll dice
      run: echo "PROCEED=$((RANDOM%2))" >> $GITHUB_ENV
      shell: bash
      
    - if: env.PROCEED == '0'
      name: Cancelling
      uses: andymckay/cancel-[email protected]
      
    - if: env.PROCEED == '0'
      name: Waiting for cancellation
      run: sleep 60
    
    # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
    - uses: actions/checkout@v2

    # rest of your steps...