Running GitHub Actions on a Randomized Schedule

GitHub Actions provide a powerful automation platform that allows developers to build, test, and deploy their projects with ease. By default, workflows are scheduled at fixed times using the cron syntax. However, sometimes it can be beneficial to run actions at random intervals to avoid predictable patterns or distribute resource usage. In this blog post, we will explore a method to run GitHub Actions on a randomized schedule by randomizing crontab times with the date and sed commands.

Setting up the Randomized Workflow

To implement a randomized GitHub Actions workflow, we will create a bash script named randomize-workflow.sh. This script will generate a random minute value and update the workflow's cron schedule accordingly.

#!/bin/bash

workflow_file=".github/workflows/example.yml"
minute=$(shuf -i 0-58 -n 1)
cron_string="$minute * * * *"

# Use sed to find and replace the cron line in the workflow file
sed -i "s/^    - cron:.*/    - cron: $cron_string/" "$workflow_file"

The script first defines the location of the workflow file and then generates a random minute value between 0 and 58 using shuf. Next, it constructs a new cron string with the randomized minute value and uses sed to update the corresponding line in the workflow file.

In the example workflow file example.yml, we have a job named "download" that runs on a fixed schedule every hour (at the 1st minute of each hour). We will replace this fixed cron schedule with our randomized cron schedule using the randomize-workflow.sh script.

Before using this script, make sure to add a secret named COMMIT_TOKEN to your GitHub repository. The COMMIT_TOKEN should contain an access token with read/write permissions to the repository running the GitHub Actions workflow. This token will be used to commit and push the changes made by the script.

Modifying the GitHub Workflow

The example.yml GitHub Actions workflow needs a few adjustments to integrate the randomization script and use the secret token. Here's the modified workflow:

name: Example Random Workflow

on:
  push:
    branches: [main]
  workflow_dispatch:
  schedule:
    - cron: 1 * * * *

jobs:
  download:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout code
        uses: actions/checkout@v3
        with:
          fetch-depth: 0
          token: ${{ secrets.COMMIT_TOKEN }}
      - name: Randomize time for next run
        run: |
          chmod +x ./randomize-workflow.sh
          ./randomize-workflow.sh
      - name: Commit & push changes
        run: |
          git config user.email "41898282+github-actions[bot]@users.noreply.github.com"
          git config user.name "github-actions[bot]"
          git add .github/workflows/example.yml
          git commit -m "Randomized GitHub Actions workflow [skip ci]"
          git pull --rebase
          git push

In the updated workflow, we added a new step named "Randomize time for next run." This step runs the randomize-workflow.sh script, which modifies the workflow's cron schedule.

Conclusion

Randomizing GitHub Actions' cron schedule can be a useful approach to distribute resource usage and avoid predictable patterns. By using a simple bash script with date, sed, and the appropriate secret token, we can update the cron schedule of the workflow programmatically.

Remember that while randomizing the schedule can add an extra layer of security or reduce resource contention, it may also introduce challenges in coordination and monitoring. Therefore, it's essential to strike a balance between randomization and predictable workflow execution based on your project's requirements.

Now you have the knowledge to implement randomized GitHub Actions workflows to enhance the automation and scheduling capabilities of your projects. Happy automating!