github-action-locks

As of April 19, 2021, GitHub now natively supports this feature and is no longer being maintained

Guarantee atomic execution of your GitHub Action workflows. Why would you want to do that, you might ask?

The reason I built this GitHub Action is specifically because Pulumi doesn't support locking remote state unless you use their SaaS offering. I deploy various bits of infrastructure using the Official Pulumi GitHub Actions and I want to be able to fearlessly merge code and watch as the updates are pushed one at a time.

Getting started

github-action-locks works by creating a record in a DynamoDB table. We rely on Conditional Writes in order to guarantee that we can't write or create the same lock record twice.

Additionally, this action works by utilizing the post-entrypoint functionality of GitHub Actions. That is to say that as long as you start this action early in your workflow, the lock will get cleaned up at the end of the job execution once all of the "post" Actions are invoked.

DynamoDB table

Here is a minimal Terraform example of what a DynamoDB table should look like for usage with this Action:

resource "aws_dynamodb_table" "github-action-locks-table" {
  name           = "github-action-locks"
  billing_mode   = "PAY_PER_REQUEST"
  hash_key       = "LockID"
  attribute {
    name = "LockID"
    type = "S"
  }
}

IAM Permissions

Here is the minimum IAM Policy required for github-action-locks to work:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "dynamodb:GetItem",
                "dynamodb:PutItem",
                "dynamodb:DeleteItem"
            ],
            "Resource": "arn:aws:dynamodb:*:*:table/github-action-locks"
        }
    ]
}

Required Environment Variables

Since we're connecting to AWS, you must set the required AWS variables for creating a session as needed by the Go AWS SDK which are AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY, and AWS_REGION. These variables will be used to create the DynamoDB client which create the locks.

Additional Configuration

There are 4 input variables that you can use to control the behavior of this action:

Input	Description	Default
`timeout`	How long to wait to acquire a lock, in minutes	`30`
`table`	DynamoDB table to write the lock in	`github-action-locks`
`key`	Name of the column where we write locks	`LockID`
`name`	Name of the lock	`foobar`

See action.yml for more information.

Example workflow

This workflow uses the workflow name as the identifier for the lock. You can use any value you want here to synchronize Actions within the same repo, workflows with multiple parallel jobs, or even Actions across repositories.

name: Main
on: [push, pull_request]

env:
  AWS_ACCESS_KEY_ID: ${{ secrets.AWS_ACCESS_KEY_ID }}
  AWS_SECRET_ACCESS_KEY: ${{ secrets.AWS_SECRET_ACCESS_KEY }}
  AWS_REGION: ${{ secrets.AWS_REGION }}
jobs:
  test:
    strategy:
      fail-fast: false
    runs-on: ubuntu-latest
    steps:
    - uses: actions/checkout@master
    - name: Create lock
      uses: abatilo/github-action-locks@v1
      with:
        timeout: "30"
        table: "github-action-locks"
        key: "LockID"
        name: "${{ github.workflow }}" # Use the workflow name, in this case "Main" as the lock identifier
    - run: |
        echo "Do something that takes a long time here"
        sleep 5

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