I worked on setting up a continuous delivery pipeline for our team, so when code is merged to a test branch, it’s automatically deployed to a test environment. I wanted to reuse the deployment pipelines already written because they do a good job handling the nuances between each microservice we deploy.

My solution at a high level was a lot like this:

1. Code is deployed to a test-branch branch.
2. A Bitbucket pipeline is kicked off that triggers the deploy.
3. The deploy script deploys a microservice to an environment, test.

This seemed really straightforward on the surface, except its a little harder than I initially thought.

Let’s imagine our Bitbucket pipelines look like this:

# deploys service-a
deploy-service-a: &deploy-service-a
  step:
    image: node:12
    name: service-a
    script:
      cd service-a
      serverless deploy --stage ${STAGE}

# sets the STAGE variable that's defined when the pipeline is manually triggered
set-variables: &set-variables
  variables:
    - name: STAGE
      default: "${STAGE}"

pipelines:
  # our custom pipeline, what shows up Bitbucket web app
  custom:
    deploy:
      - <<: *set-variables
      - <<: *deploy-service-a

How this works:

1. A developer manually triggers the deploy pipeline, specifying the STAGE variable in the Bitbucket web app
2. STAGE is set and assigned to the STAGE variable via set-variables
3. deploy-service-a is kicked off, executes, and deploys new code for service-a in the appropriate stage.

Struggle

This works well for manual deployments. However, I needed to have this triggered automatically. So I update the pipelines object and added:

pipelines:

  branches:
    test-branch:
      - <<: *deploy

Theoretically, this triggers deploy to execute whenever there is a commit to test-branch, however this fails spectacularly because the STAGE variable is not defined.

I try the following:

pipelines:

  branches:
    variables:
      - name: STAGE
        default: test
    test-branch:
      - <<: *deploy

I soon find out that you can only add a variables object to custom pipelines. Honestly, this is where I start to lose my mind, having spent hours on something that should be simple and straightforward.

Solution

Fortunately, for me, I’m able to string together a correct seqeuence of characters and words and executed the perfect Google search and found a solution on StackOverflow.

First, there were a few limitations of Bitbucket I hadn’t realized until I went on this journey:

1. Only custom pipelines can have a variables object.
2. You cannot pass variables between steps (because each step is it’s own deploy, with it’s own scope, docker image, variables, etc.).

However, I learned I can get around this by using artifacts. We’d normally use artifacts to save packaged binaries or test results that were executed during a Bitbucket pipeline run. They can be used to pass data between steps as well.

Armed with my newly found knowledge, by Bitbucket pipelines were refactored into:

deploy-service-a: &deploy-service-a
  step:
    image: node:12
    name: service-a
    script:
      - if [ -e set_env.sh ]; then
      -   cat set_env.sh
      -   source set_env.sh
      - fi
      cd service-a
      serverless deploy --stage ${STAGE}

set-variables: &set-variables
  variables:
    - name: STAGE
      default: "${STAGE}"

pipelines:
  custom:
    deploy:
      - <<: *set-variables
      - <<: *deploy-service-a
  
  branches:
    test-branch:
      - step:
        name: Save stage
        script: 
          - STAGE="test"
          - echo $STAGE
          - echo "export STAGE=$STAGE" >> set_env.sh
        artifacts:
          - set_env.sh
      - <<: *deploy

This works perfectly. If you look closely to the output when running this Bitbucket pipeline, you’ll see something in deploy-service-a's Build setup phase that resembles:

Artifact "set_env.sh": Downloading
Artifact "set_env.sh": Downloaded 140 B in 0 seconds
Artifact "set_env.sh": Extracting
Artifact "set_env.sh": Extracted in 0 seconds

Artifacts from previous steps are passed to subsequent steps!