Dependencies

When one component’s image depends on another, you need to tell EMB so it builds them in the right order.

Declaring Dependencies

In a component’s Embfile, use the dependencies array:

cat worker/Embfile.yml

description: Background job worker

resources:
  image:
    type: docker/image
    publish: true
    dependencies:
      - base:image

tasks:
  test:
    description: Run worker tests
    script: npm test

  scale:
    description: Show scaling info
    script: echo "Worker concurrency is controlled by WORKER_CONCURRENCY env var"
    executors:
      - local

The key part is:

resources:
  image:
    type: docker/image
    dependencies:
      - base:image    # Build base:image first

This tells EMB: “Before building worker:image, make sure base:image is built.”

Dependency Format

Dependencies use the format component:resource:

• base:image - The image resource of the base component
• api:image - The image resource of the api component

Viewing Dependencies

See all resources and their dependencies:

emb resources

 ID             NAME   TYPE          PUBLISHABLE  REFERENCE
-------------------------------------------------------------------------------
 api:image      image  docker/image  ✓            microservices/api:latest
 base:image     image  docker/image               microservices/base:latest
 gateway:image  image  docker/image  ✓            microservices/gateway:latest
 worker:image   image  docker/image  ✓            microservices/worker:latest

The API Component

The API also depends on base:

cat api/Embfile.yml

description: REST API service

resources:
  image:
    type: docker/image
    publish: true
    dependencies:
      - base:image

tasks:
  test:
    description: Run API tests
    pre:
      - lint
    script: npm test

  lint:
    description: Run linter
    script: npm run lint

Both api and worker depend on base, meaning base must be built first.

Why Declare Dependencies?

Without explicit dependencies, EMB might try to build worker before base exists, causing the build to fail. Dependencies ensure:

1. Correct build order - Parents built before children
2. Parallel optimization - Independent components can build simultaneously
3. Rebuild detection - If base changes, dependents are rebuilt

Next Step

Continue to Build Ordering to see how EMB resolves the complete build graph.