Deploy PR Preview action

GitHub Action that deploys previews of pull requests to GitHub Pages. Works on any repository with a GitHub Pages site.

Features:

• Creates and deploys previews of pull requests to your GitHub Pages site
• Leaves a comment on the pull request with a link to the preview so that you and your team can collaborate on new features faster
• Updates the deployment and the comment whenever new commits are pushed to the pull request
• Cleans up after itself — removes deployed previews when the pull request is closed
• Can be configured to override any of these behaviours

Preview URLs look like this: https://[owner].github.io/[repo]/pr-preview/pr-[number]/

Pictured: rossjrw#1

This Action does not currently support deploying previews for PRs from forks, but will do so in the upcoming v2.

Usage

A GitHub Actions workflow is required to use this Action.

All the workflow needs to do first is checkout the repository and build the Pages site.

First, ensure that your repository is configured to have its GitHub Pages site deployed from a branch, by setting the source for the deployment under Settings > Pages of your repository to Deploy from branch:

Pictured: Repository Pages settings at /settings/page

The gh-pages branch is used for GitHub Pages deployments by convention, and will be used in examples here as well.

If your GitHub pages site is deployed from the gh-pages branch, built with e.g. an npm script to the ./build/ dir, and you're happy with the default settings, usage is very simple:

# .github/workflows/preview.yml
name: Deploy PR previews

on:
  pull_request:
    types:
      - opened
      - reopened
      - synchronize
      - closed

concurrency: preview-${{ github.ref }}

jobs:
  deploy-preview:
    runs-on: ubuntu-20.04
    steps:
      - name: Checkout
        uses: actions/checkout@v2

      - name: Install and Build
        run: |
          npm install
          npm run build

      - name: Deploy preview
        uses: rossjrw/pr-preview-action@v1
        with:
          source-dir: ./build/

Important things to be aware of

Run only when files are changed

Consider limiting this workflow to run only when relevant files are edited to avoid deploying previews unnecessarily.

Run on all appropriate pull request events

Be sure to pick the right event types for the pull_request event. It only comes with opened, reopened, and synchronize by default — but this Action assumes by default that the preview should be removed during the closed event, which it only sees if you explicitly add it to the workflow.

Grant Actions permission to read and write to the repository

This must be changed in the repository settings by selecting "Read and write permissions" at Settings > Actions > General > Workflow permissions. Otherwise, the Action won't be able to make any changes to your deployment branch.

Set a concurrency group

I highly recommend setting a concurrency group scoped to each PR using github.ref as above, which should prevent the preview and comment from desynchronising if you are e.g. committing very frequently.

Ensure your main deployment is compatible

If you are using GitHub Actions to deploy your GitHub Pages sites (typically on push to the main branch), there are some actions you should take to avoid the PR preview overwriting the main deployment, or vice-versa.

1. Prevent your main deployment from deleting previews

   If your root directory on the GitHub Pages deployment branch (or docs/ on the main branch) is generated automatically (e.g. on pushes to the main branch, with a tool such as Webpack), you will need to configure it not to remove the umbrella directory (pr-preview/ by default, see configuration below).

   For example, if you are using JamesIves/github-pages-deploy-action to deploy your build, you can implement this using its clean-exclude parameter:

   # .github/workflows/build-deploy-pages-site.yml
   steps:
     ...
     - uses: JamesIves/github-pages-deploy-action@v4
       ...
       with:
         clean-exclude: pr-preview/
         ...

   If you don't do this, your main deployment may delete all of your currently-existing PR previews.

2. Don't force-push your main deployment

   Force-pushing your main deployment will cause it to overwrite any and all files in the deployment location. This will destroy any ongoing preview deployments. Instead, consider adjusting your deployment workflow to rebase or merge your main deployment onto the deployment branch such that it respects other ongoing deployments.

   For example, if you are using JamesIves/github-pages-deploy-action to deploy your build, be aware that at the time of writing (v4.3.0) it force-pushes new deployments by default. You can disable this by setting its force parameter to false, which will prompt it to rebase new deployments instead of force-pushing them:

   # .github/workflows/build-deploy-pages-site.yml
   steps:
     ...
     - uses: JamesIves/github-pages-deploy-action@v4
       ...
       with:
         force: false
         ...

   This feature was introduced in v4.3.0 of the above Action.

Configuration

The following configuration settings are provided, which can be passed to the with parameter.

• source-dir: Directory containing files to deploy.

  E.g. if your project builds to ./dist/ you would put ./dist/ (or just dist) here. For the root directory of your project, put . here.

  Equivalent to JamesIves/github-pages-deploy-action 'folder' setting.

  Will be ignored when removing a preview.

  Default: .

• preview-branch: Branch on which the previews will be deployed. This should be the same branch that your GitHub Pages site is deployed from.

  Default: gh-pages

• umbrella-dir: Name of the directory containing all previews. All previews will be created inside this directory.

  The umbrella directory is used to namespace previews from your main branch's deployment on GitHub Pages.

  Set to . to place preview directories into the root directory, but be aware that this may cause your main branch's deployment to interfere with your preview deployments (and vice-versa!)

  Default: pr-preview

• (Advanced) action: Determines what this action will do when it is executed. Supported values: deploy, remove, none, auto.

  • deploy: will attempt to deploy the preview and overwrite any existing preview in that location.
  • remove: will attempt to remove the preview in that location.
  • auto: the action will try to determine whether to deploy or remove the preview based on the emitted event. It will deploy the preview on pull_request.types.opened, .reopened and .synchronize events; and remove it on pull_request.types.closed events. It will not do anything for all other events, even if you explicitly specify that the workflow should run on them.
  • none and all other values: the action will not do anything.

  Default value: auto

Outputs

• deployment-url: the URL at which the preview has been deployed.

Examples

Full example

Full example with all default values added:

# .github/workflows/preview.yml
name: Deploy PR previews
concurrency: preview-${{ github.ref }}
on:
  pull_request:
    types:
      - opened
      - reopened
      - synchronize
      - closed
jobs:
  deploy-preview:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - run: npm i && npm run build
      - uses: rossjrw/pr-preview-action@v1
        with:
          source-dir: .
          preview-branch: gh-pages
          umbrella-dir: pr-preview
          action: auto

...and an accompanying main deployment workflow:

# .github/workflows/deploy.yml
name: Deploy PR previews
on:
  push:
    branches:
      - main
jobs:
  deploy-preview:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - run: npm i && npm run build
      - uses: JamesIves/github-pages-deploy-action@v4
        with:
          folder: .
          branch: gh-pages
          clean-exclude: pr-preview

Deployment from docs/

If your Pages site is built to build/ and deployed from the docs/ directory on the main branch:

# .github/workflows/preview.yml
steps:
  ...
  - uses: rossjrw/pr-preview-action@v1
    with:
      source-dir: build
      preview-branch: main
      umbrella-dir: docs/pr-preview

You should definitely limit this workflow to run only on changes to directories other than docs/, otherwise this workflow will call itself recursively.

Only remove previews for unmerged PRs

Information from the context and conditionals can be used to make more complex decisions about what to do with previews; for example, removing only those associated with unmerged PRs when they are closed:

# .github/workflows/preview.yml
steps:
  ...
  - uses: rossjrw/pr-preview-action@v1
    if: contains(['opened', 'reopened', 'synchronize'], github.event.action)
    with:
      source-dir: ./build/
      action: deploy
  - uses: rossjrw/pr-preview-action@v1
    if: github.event.action == "closed" && !github.event.pull_request.merged
    with:
      source-dir: ./build/
      action: remove

Permanent previews

If you want to keep PR previews around forever, even after the associated PR has been closed, you don't want the cleanup behaviour of auto — call deploy and never call remove:

# .github/workflows/everlasting-preview.yml
name: Deploy everlasting PR preview
concurrency: preview-${{ github.ref }}
on:
  pull_request:
    types:
      - opened
      - synchronize
jobs:
  deploy-preview:
    runs-on: ubuntu-20.04
    steps:
      - uses: actions/checkout@v2
      - run: npm i && npm run build
      - uses: rossjrw/pr-preview-action@v1
        with:
          source-dir: ./build/
          action: deploy

Acknowledgements

Big thanks to the following:

• shlinkio/deploy-preview-action (MIT), prior art that informed the direction of this Action
• JamesIves/github-pages-deploy-action (MIT), used by this Action to deploy previews
• marocchino/sticky-pull-request-comment (MIT), used by this Action to leave a sticky comment on pull requests