Intro

This project originated from https://github.com/tuler/s3-check-action and was created in response to the set-output deprecated issue

GitHub Action to check if a file exists in an S3 Bucket

⚠️ Note: To use this action, you must have access to the GitHub Actions feature. GitHub Actions are currently only available in public beta. You can apply for the GitHub Actions beta here.

This simple action uses the vanilla AWS CLI to check if a file exists in an S3 bucket, and set an output to true or false. This is useful to "short-circuit" a job and not do unnecessary subsequent steps.

Usage

This action is particularly useful for scheduled builds (a.k.a nightly builds). You don't need to do all the work again if you already have the results from the previous execution, and nothing has changed since then.

GitHub Actions does not provide a way to verify this, so you have to rely on an external flag to control this behaviour.

This action relies on an file you host in a S3 bucket. Your build can write a file with the name of the ${GITHUB_SHA}, and before executing the build steps check if the file already exists. If it exists the build does not fail, but creates an output variable that you can check before running the build steps.

workflow.yml Example

Place in a .yml file such as this one in your .github/workflows folder. Refer to the documentation on workflow YAML syntax here.

name: Check if Static file exists in S3 Bucket
on:
  schedule:
    - cron: '0 0 * * *'

jobs:
  deploy:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - uses: SilverNine/s3-file-exists@v1
        env:
          FILE: ${{ github.sha }}
          AWS_S3_REGION: 'us-east-1'
          AWS_S3_BUCKET: ${{ secrets.AWS_S3_BUCKET }}
          AWS_ACCESS_KEY_ID: ${{ secrets.AWS_ACCESS_KEY_ID }}
          AWS_SECRET_ACCESS_KEY: ${{ secrets.AWS_SECRET_ACCESS_KEY }}
      - name: Fail if Static file does not exist
        run: echo "ERROR: Static file not found in S3 bucket"
        if: ${{ env.S3_FILE_EXISTS == 'false' }}
      - name: Success if Static file does exist
        run: echo "Write a file to S3 bucket with name \${GITHUB_SHA}"
        if: ${{ env.S3_FILE_EXISTS == 'true' }}

Configuration

The following settings must be passed as environment variables as shown in the example. Sensitive information, especially AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY, should be set as encrypted secrets — otherwise, they'll be public to anyone browsing your repository.

Key	Value	Suggested Type	Required
AWS_ACCESS_KEY_ID	Your AWS Access Key. More info here.	secret	Yes
AWS_SECRET_ACCESS_KEY	Your AWS Secret Access Key. More info here.	secret	Yes
AWS_S3_BUCKET	The name of the bucket you're syncing to. For example, jarv.is.	secret	Yes
AWS_S3_REGION	The region where you created your bucket in. For example, us-east-1. Full list of regions here.	env	Yes
FILE	The file to check	env	Yes

License

This project is distributed under the MIT license.