Building and pushing Docker images to Azure Container Registry is simple with a small GitHub Actions workflow.

This blog post assumes you’ve got a docker-compose.yml file in your GitHub repository. If you’re just using a Dockerfile, you’ll need to make a tiny amendment to the Build Docker image step in the push-to-acr.yml file described below.

Microsoft Azure setup/configuration

If you’re starting fresh, in terms of our Azure setup we’ll need:

• a Resource Group;
• an Azure Container Registry (ACR);
• and an access key so that we can access our ACR programmatically from our GitHub Actions workflow.

If you’ve already got this configured, you can skip to the next section.

I’ll use PowerShell to create this. First, our Resource Group.

New-AzResourceGroup -Name "mydemoappghatoacr" -Location "UK South"

With that done, we’ll create our ACR within this Resource Group.

New-AzContainerRegistry -ResourceGroupName "mydemoappghatoacr" -Name "mydemoappghatoacr" -Sku "Basic" -EnableAdminUser

Finally, let’s grab the access key values we’ll need to connect to our ACR from our GitHub Actions workflow.

Get-AzContainerRegistryCredential -ResourceGroupName "mydemoappghatoacr" -Name "mydemoappghatoacr"

Make a note of the Username and Password values from this response.

GitHub Actions workflow

Before we create our GitHub Actions workflow, we’ll add a couple of Actions secrets to our GitHub repository. These are encrypted environment variables that can be used within our GitHub Actions workflow(s), which stops us from exposing values that we want to remain secure, such as our Microsoft Azure client ID and secret.

Head to your GitHub repository, and navigate to the Settings screen. In here, you should be able to find a Secrets section under the Security subheading. Secrets currently allows you to configure secrets for Actions, Codespaces, and Dependabot. Select Actions, and then click ‘New repository secret’.

We’ll be adding three Actions secrets:

1. ACR_REGISTRY_NAME, containing the name of your ACR.
2. AZ_SP_CLIENT_ID containing the Username value you noted earlier.
3. AZ_SP_CLIENT_SECRET containing the Password value you noted earlier.

In your repository, create a new directory named .github. Inside here, we’ll create another new directory named workflows, inside which we’ll add a new empty file named push-to-acr.yml, with the resulting file path being .\.github\workflows\push-to-acr.yml.

First, we’ll give our workflow a name, and some run configuration. In this case we’re telling GitHub Actions to run this workflow when we push code to our main branch.

Secondly, we’re checking out the repository code.

name: Push to Azure Container Registry
on:
  push:
    branches:
      - main

jobs:
  push-to-azure-container-registry:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout repository
        uses: actions/checkout@main

In order for our GitHub Actions workflow to push to ACR, it’ll need to authenticate using the credentials we’ve stored as GitHub Actions secrets. To do this, we’ll use the Azure Container Registry Login GitHub Action available on the GitHub Marketplace. This GitHub Action will handle the authentication for us, we just need to tell it what values to use.

- name: Login to Azure Container Registry
        uses: azure/docker-login@v1
        with:
          login-server: ${{ secrets.ACR_REGISTRY_NAME }}.azurecr.io
          username: ${{ secrets.AZ_SP_CLIENT_ID }}
          password: ${{ secrets.AZ_SP_CLIENT_SECRET }}

Next, we’ll add a simple step to our workflow that will build our Docker image.

- name: Build Docker image
run: docker-compose build

Our workflow is now capable of checking out our codebase and building our Docker image. The final step is to push this image to our pre-configured Azure Container Registry.

Let’s add this final step to our workflow. This last step will tag the image we’ve just built with the Git commit SHA, and then push this tagged image to ACR.

- name: Push Docker image to Azure Container Registry
  run: |
    docker tag mydemoapp:latest ${{ secrets.ACR_REGISTRY_NAME }}.azurecr.io/mydemoapp:${{ github.sha }}
    docker push ${{ secrets.ACR_REGISTRY_NAME }}.azurecr.io/mydemoapp:${{ github.sha }}    

Our full GitHub Actions workflow file looks like the following:

name: Push to Azure Container Registry
on:
  push:
    branches:
      - main

jobs:
  push-to-azure-container-registry:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout repository
        uses: actions/checkout@main

      - name: Login to Azure Container Registry
        uses: azure/docker-login@v1
        with:
          login-server: ${{ secrets.ACR_REGISTRY_NAME }}.azurecr.io
          username: ${{ secrets.AZ_SP_CLIENT_ID }}
          password: ${{ secrets.AZ_SP_CLIENT_SECRET }}

      - name: Build Docker image
        run: docker-compose build

      - name: Push Docker image to Azure Container Registry
        run: |
            docker tag mydemoapp:latest ${{ secrets.ACR_REGISTRY_NAME }}.azurecr.io/mydemoapp:${{ github.sha }}
            docker push ${{ secrets.ACR_REGISTRY_NAME }}.azurecr.io/mydemoapp:${{ github.sha }}