docker-image.md

Building Docker Images

Next step is to have our application packaged as a docker image for easy distribution.

We have some requirements for our pipeline step:

• Should build our application as a docker image.
• Should tag the image with both the git sha and "latest". (Do not use such general tags in real life!)
• Should push the image to Githubs docker registry.

In order for this to work, we need three environment variables:

• docker_username the username for docker registry.
• docker_password the password for docker registry.
• GIT_COMMIT the name of the git commit that is being built.

You can set these environment variables as global variables in your workflow through the env section.

env:
  docker_username: <your docker username>
  docker_password: <your docker password>
  GIT_COMMIT: <your git commit>

The two scripts: ci/build-docker.sh and ci/push-docker.sh expects all three environment variables to be set.

Build-in environment variables

Many of the common information pieces for a build is set in default environment variables.

Examples of these are:

• The name of the repository
• The name of the branch
• The SHA of the commit

You can see the ones you can use directly inside a step here: https://docs.github.com/en/actions/learn-github-actions/environment-variables#default-environment-variables

Github Actions also has a list of contexts.

Contexts are a way to access information about workflow runs, runner environments, jobs, and steps. Each context is an object that contains properties, which can be strings or other objects. You can see them here: https://docs.github.com/en/actions/learn-github-actions/contexts#about-contexts

The default environment variables that GitHub sets are available to every step in a workflow. Contexts are also available before the steps, as when defining the env section of the workflow.

Tasks

• Add a new job named Docker-image that requires the Build to be completed. You need to add package write permissions so that your action can upload the container to the registry.

  Docker-image:
    runs-on: ubuntu-latest
    needs: [Build]
    permissions:
      packages: write

In order for us to create and push the docker image, we need the CI scripts, the Dockerfile and the Artifact. All of them are present in the code artifact created in the last exercise.

• Add a step in Docker-image which downloads the code artifact.

💡 Hint on how it looks like

    - name: Download code
      uses: actions/download-artifact@v4
      with:
        name: code
        path: .

• Add docker_username and docker_password as environmental variables on top of the workflow file.

name: Main workflow
on: push
env: # Set the secret as an input
  docker_username: ${{ github.actor }} 
  docker_password: ${{ secrets.GITHUB_TOKEN }} #Nees to be set to be made available to the workflow
jobs:
  Build:

💡 The docker_username should be set to the github.actor. If your username is having capital letters, you need to type it in manually as Docker will not accept capital letters in the repository name.

#  docker_username: ${{ github.actor }} 
docker_username: elmeri #instead of Elmeri

• Add GIT_COMMIT environment variable as well, that should contain the commit sha of the repository.

Tip! it needs the same "wrapping" (${{}}) as the other environment variables, and can be found in the github context.

• Run the ci/build-docker.sh and ci/push-docker.sh scripts.

Ready steps looks like:

    - name: build docker
      run: bash ci/build-docker.sh
    - name: push docker
      run: bash ci/push-docker.sh

Hint: The reason we have bash first is to bypass the file permissions. If you don't do this, you will get a permission denied error.

• Submit your changes, and see that the image is built and pushed to the GitHub container registry.

Tip! You can find the image under the Packages tab on your profile.

Using actions instead of scripts

The above job can be also done by using actions: docker/login-action@v3 and docker/build-push-action@v5, what will provide the same functionality. You can find it in the example below:

Doing the same using Actions

on: push
jobs:
  build-and-push-latest:
    runs-on: ubuntu-latest
    permissions:
      packages: write
    steps:
      - name: Login to DockerHub
        uses: docker/login-action@v3
        with:
          registry: ghcr.io
          username: ${{ github.actor }}
          password: ${{ secrets.GITHUB_TOKEN }}
      - name: Build and push
        uses: docker/build-push-action@v5
        with:
          context: app
          push: true
          tags: ghcr.io/${{ github.actor }}/micronaut-app:1.0-${{ github.sha }},ghcr.io/${{ github.actor }}/micronaut-app:latest

Solution

If you strugle and need to see the whole Solution you can click this link

Results

You should be able to see your docker image on your GitHub account as: