Configure Docker Image Tagging in Azure DevOps

Let’s say you have:

• a Python REST API and you use Docker to containerize it.
• two environments (Production and QA) on Azure Cloud Services.
• a DevOps pipeline that builds and push the Docker image to a Container Registry on Azure and tag the latest image with latest tag.

Next, you have a DevOps branch policy to trigger a build on an Individual CI trigger when something is pushed to main or develop.

With the above, the result is that DevOps creates an image tagged latest on both triggers.

Wouldn’t it be better to distinguish the two Docker image created and be able to test the build from the develop branch on the QA environment?

Yes, it would.

Here is how to modify the pipeline.

Modifiy the Pipeline

To begin, let’s define the need:

• on a Merge Request or Individual CI on develop, we want to push an image tagged ready-for-qa.
• on a Merge Request or Individual CI on main, we want to push an image tagged latest.

The Trigger

First, you need to define the trigger in the azure-pipelines.yml file:

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trigger:
  branches:
    include:
      - main
      - develop

Evaluate the Image Tag

Next, let’s evaluate the image tag. You’ll use it in the bash script.

Under a Build and push stage, add a Build job and a bash step where you evaluate the container tag:

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- task: Bash@3
  displayName: Set image tags
  inputs:
    targetType: "inline"
    script: |
      if [ "$(Build.SourceBranch)" = "refs/heads/develop" ]; then
        echo "##vso[task.setvariable variable=imageTags]ready-qa"
      elif [ "$(Build.SourceBranch)" = "refs/heads/main" ]; then
        echo "##vso[task.setvariable variable=imageTags]$(Build.BuildId),latest"
      else
        echo "##vso[task.setvariable variable=imageTags]$(Build.BuildId)"
      fi      

  name: setImageTagsStep

Build and Push To the Container Registry

Let’s then modify the next steps to build and push an image to the container registry with the computed image tag:

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- task: Docker@2
  displayName: Build image
  inputs:
    command: build
    repository: $(imageRepository)
    dockerfile: $(dockerfilePath)
    buildContext: $(projectPath)
    containerRegistry: $(dockerRegistryServiceConnection)
    tags: |
      $(imageTags)      

- task: Docker@2
  displayName: Push image to container registry
  inputs:
    command: push
    repository: $(imageRepository)
    containerRegistry: $(dockerRegistryServiceConnection)
    tags: |
      $(imageTags)      

The build and push are split because, in the case that you build a container and pass it an application version number, the build phase will take an argument with the computed version. The step buildAndPush that Azure provides doesn’t allow argument.

I’ll demonstrate this in a future article.

Conclusion

This approach is an opinionated approach, but it worked well for me. You could possibly perform a similar outcome in a different way.

If you like my approach…

Photo by Kaique Rocha.