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Dev Container Build and Run GitHub Action

The Dev Container Build and Run GitHub Action is aimed at making it easier to re-use Dev Containers in a GitHub workflow. The Action supports using a Dev Container to run commands for CI, testing, and more along with pre-building Dev Container image. Dev Container image building supports Dev Container Features and automatically places Dev Container metadata on an image label for simplified use.

NOTE: This Action cannot currently take advantage of pre-built Codespaces. However, you can create or use pre-built container images.

Getting Started

The simplest example of using the action is shown below:

name: 'build' 
on: # rebuild any PRs and main branch changes
  pull_request:
  push:
    branches:
      - main

jobs:
  build:
    runs-on: ubuntu-latest
    steps:

      - name: Checkout (GitHub)
        uses: actions/checkout@v3

      - name: Build and run dev container task
        uses: devcontainers/[email protected]
        with:
          # Change this to be your CI task/script
          runCmd: yarn test

With the example above, each time the action runs it will rebuild the Docker image for the dev container. To save time in builds, you can push the dev container image to a container registry (e.g. GitHub Container Registry) and re-used the cached image in future builds.

To enable pushing the dev container image to a container registry you need to specify a qualified imageName and ensure that your GitHub workflow is signed in to that registry.

The example below shows installing Docker BuildKit, logging in to GitHub Container Registry, and then building and running the dev container with the devcontainer-build-run action:

name: 'build' 
on: # rebuild any PRs and main branch changes
  pull_request:
  push:
    branches:
      - main

jobs:
  build:
    runs-on: ubuntu-latest
    steps:

      - name: Checkout (GitHub)
        uses: actions/checkout@v3

      - name: Login to GitHub Container Registry
        uses: docker/login-action@v2 
        with:
          registry: ghcr.io
          username: ${{ github.repository_owner }}
          password: ${{ secrets.GITHUB_TOKEN }}

      - name: Build and run Dev Container task
        uses: devcontainers/[email protected]
        with:
          # Change this to point to your image name
          imageName: ghcr.io/example/example-devcontainer
          # Change this to be your CI task/script
          runCmd: |
            # Add multiple commands to run if needed
            make install-packages
            make ci-build

In the example above, the devcontainer-build-run will perform the following steps:

  1. Build the dev container using the .devcontainer/devcontainer.json from the root of the repo
  2. Run the dev container with the make ci-build command specified in the runCmd input
  3. If the run succeeds (and we're not building from a PR branch) then push the image to the container registry. This enables future image builds in step 1 to use the image layers as a cache to improve performance

The devcontainers/ci action uses Docker BuildKit to perform the Docker builds as this has support for storing layer cache metadata with the image. This is installed by default on hosted runners, but you can use the docker/setup-buildx-action to install this on your own runners.

Other examples

Pre-building an image:

- name: Pre-build dev container image
  uses: devcontainers/[email protected]
  with:
    imageName: ghcr.io/example/example-devcontainer
    cacheFrom: ghcr.io/example/example-devcontainer
    push: always

Using a Dev Container for a CI build:

- name: Run make ci-build in dev container
  uses: devcontainers/[email protected]
  with:    
    # [Optional] If you have a separate workflow like the one above
    # to pre-build your container image, you can reference it here
    # to speed up your application build workflows as well!
    cacheFrom: ghcr.io/example/example-devcontainer

    push: never
    runCmd: make ci-build

Both at once:

- name: Pre-build image and run make ci-build in dev container
  uses: devcontainers/[email protected]
  with:
    imageName: ghcr.io/example/example-devcontainer
    cacheFrom: ghcr.io/example/example-devcontainer
    push: always
    runCmd: make ci-build

Inputs

Name Required Description
imageName true Image name to use when building the dev container image (including registry)
imageTag false One or more comma-separated image tags (defaults to latest)
subFolder false Use this to specify the repo-relative path to the folder containing the dev container (i.e. the folder that contains the .devcontainer folder). Defaults to repo root
configFile false Use this to specify the repo-relative path to the devcontainer.json file. Defaults to ./.devcontainer/devcontainer.json and ./.devcontainer.json.
runCmd true The command to run after building the dev container image
env false Specify environment variables to pass to the dev container when run
inheritEnv false Inherit all environment variables of the runner CI machine
checkoutPath false Only used for development/testing
push false Control when images are pushed. Options are never, filter, always. For filter, images are pushed if the refFilterForPush and eventFilterForPush conditions are met. Defaults to filter if imageName is set, never otherwise.
refFilterForPush false Set the source branches (e.g. refs/heads/main) that are allowed to trigger a push of the dev container image. Leave empty to allow all (default)
eventFilterForPush false Set the event names (e.g. pull_request, push) that are allowed to trigger a push of the dev container image. Defaults to push. Leave empty for all
skipContainerUserIdUpdate false For non-root Dev Containers (i.e. where remoteUser is specified), the action attempts to make the container user UID and GID match those of the host user. Set this to true to skip this step (defaults to false)
cacheFrom false Specify additional images to use for build caching
noCache false Builds the image with --no-cache (takes precedence over cacheFrom)
platform false Platforms for which the image should be built. If omitted, defaults to the platform of the GitHub Actions Runner. Multiple platforms should be comma separated.

Outputs

Name Description
runCmdOutput The output of the command specified in the runCmd input

Specifying a sub-folder

Suppose your repo has the following structure:

<repo-root>
|-folderA
|-folderB
| |-.devcontainer
| | |-devcontainer.json
| | |-Dockerfile
| |-main.go
|-folderC
...

To build and run the dev container from folderB you can specify the subFolder input as shown below.

      - name: Build and run dev container task
        uses: devcontainers/[email protected]
        with:
          subFolder: folderB
          imageName: ghcr.io/example/example-devcontainer
          runCmd: make ci-build

Environment Variables

If you want to pass additional environment variables to the dev container when it is run, you can use the env input as shown below.

      - name: Build and run dev container task
        uses: devcontainers/[email protected]
        env:
          WORLD: World
        with:
          subFolder: folderB
          imageName: ghcr.io/example/example-devcontainer
          runCmd: echo "$HELLO - $WORLD"
          env: |
            HELLO=Hello
            WORLD

In this example, the HELLO environment variable is specified with the value Hello in the env input on the devcontainer-build-run step. The WORLD environment variable is specified without a value so will pick up the value that is assigned in the standard action's env configuration (it could also be picked up from the job environment variables - see the GitHub Action Environment Variables docs for more information).

The result from running the container is to output "Hello - World".

The environment variables specified in the workflow step are passed along when the run-command is executed. Therefore, they replace environment variables with the same name that are set either directly in the Dockerfile or the devcontainer.json under the containerEnv key.

remoteEnv

If you have environment variables set in the remoteEnv section of your devcontainer.json file using localEnv references, you need to pass the environment variables in a specific way.

Since localEnv references are resolved by the devcontainer CLI, we need to ensure that we set the values in the correct context for localEnv. To do this, the values should be set using the env property on the action, not using the env nested under the with block.

For example, if you have the following section in your devcontainer.json:

{
    "remoteEnv": {
        "HELLO": "${localEnv:HELLO}"
    }
}

You should set the HELLO environment variable using the env property on the action, not using the env nested under the with block.

      - name: Build and run dev container task
        uses: devcontainers/[email protected]
        env:
          # Set HELLO here so that it is resolved via the localEnv context
          HELLO: hello
        with:
          imageName: ghcr.io/example/example-devcontainer
          runCmd: echo "$HELLO"
          # Don't use the env block here to set the HELLO environment variable
          # as it will be overridden by the value from localEnv context
          # when the CLI starts the container

Multi-Platform Builds

Builds for multiple platforms have special considerations, detailed at mutli-platform-builds.md.