Dev Container Build and Run Task

The Dev Container Build and Run Azure DevOps task is aimed at making it easier to re-use a Dev Container in an Azure DevOps pipeline. It 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.

Getting Started

The simplest example of using the action is shown below:

trigger:
- main

pool:
  vmImage: ubuntu-latest

steps:

- task: DevcontainersCi@0
  inputs:
    # Change this to be your CI task/script
    runCmd: 'make ci-build'

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. Azure 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 ensure that your pipeline is signed in to that registry.

The DevcontainersCi task uses Docker BuildKit to perform the Docker builds as this has support for storing layer cache metadata with the image. A version of Docker that supports BuiltKit is installed on the default hosted agents - if using a custom agent ensure that you make BuildKit available.

The example below shows logging in to an Azure Container Registry instance, and then building and running the dev container with the devcontainer-build-run action:

trigger:
- main

pool:
  vmImage: ubuntu-latest

steps:
# Replace the username and registry name here with your own details
# This step also uses an ACR_TOKEN specified as a secret variable
- script: |
    docker login -u test -p $ACR_TOKEN yourregistry.azurecr.io
  displayName: 'Log in to Container Registry'
  env:
    ACR_TOKEN: $(ACR_TOKEN)

- task: DevcontainersCi@0
  inputs:
    # Change this to point to your image name
    imageName: 'yourregistry.azurecr.io/example-dev-container'
    # Change this to be your CI task/script
    runCmd: 'make ci-build'
    # sourceBranchFilterForPush allows you to limit which branch's builds
    # are pushed to the registry
    sourceBranchFilterForPush: refs/heads/main

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

Inputs

Outputs

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.

- task: DevcontainersCi@0
  inputs:
    imageName: 'yourregistry.azurecr.io/example-dev-container'
    subFolder: folderB
    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.

- task: DevcontainersCi@0
  inputs:
    imageName: 'yourregistry.azurecr.io/example-dev-container'
    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 task's env configuration.

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

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.

- task: DevcontainersCi@0
  env:
    WORLD: World
  inputs:
    imageName: 'yourregistry.azurecr.io/example-dev-container'
    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 Azure DevOps Piplines 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 task, 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 task, not using the env nested under the with block.

- task: DevcontainersCi@0
  env:
    # Set HELLO here so that it is resolved via the localEnv context
    HELLO: hello
  inputs:
    imageName: 'yourregistry.azurecr.io/example-dev-container'
    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.