On-Demand Build for Monorepo

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This article introduces how to achieve on-demand builds in a Monorepo scenario — triggering build tasks only for modified directories, avoiding the resource waste and time overhead of full builds.

Prerequisites

Syntax guide: Pipeline.ifModify
System default environment variables: CNB_PIPELINE_KEY

Example Configuration

# Use YAML anchor for configuration reuse
.docker-build-pipeline: &docker-build-pipeline
  services:
    # Once declared, docker commands can be used directly within the pipeline
    - docker
  ifModify:
    # Specifies that the build is triggered only when files in this directory are modified.
    # Here, CNB_PIPELINE_KEY is a system default environment variable representing the current pipeline's KEY
    - packages/${CNB_PIPELINE_KEY}/**
  stages:
    - name: set docker tag
      script: echo -n "${CNB_DOCKER_REGISTRY}/${CNB_REPO_SLUG_LOWERCASE}:$CNB_COMMIT_SHORT"
      exports:
        info: IMAGE_TAG

    - name: docker build
      script: cd packages/${CNB_PIPELINE_KEY} && docker build -t $IMAGE_TAG .

    - name: push image
      script: docker push $IMAGE_TAG

main:
  push:
    package-1: *docker-build-pipeline
    package-2: *docker-build-pipeline