Docker & Kubernetes: Ship with Confidence

Checkpoint: Local Environments with Docker Compose

Five questions on this section. Answer all of them, then see your score and why each answer is right or wrong.

In Compose, the api service’s DATABASE_URL is postgres://notes:notes@db:5432/notes. You rename the service from db to postgres and run docker compose up -d --remove-orphans. What happens?

Nothing changes; Compose keeps the old DNS name as an alias.
Compose rewrites DATABASE_URL to match.
Both names resolve, because the volume is still called pgdata.
The API can no longer resolve db and fails to connect until you update the URL host to postgres.

You run docker compose down, edit db/init/002-seed.sql, and run docker compose up -d. The seed data doesn’t appear. Why?

down deleted the bind mount.
Init scripts run in reverse order.
The pgdata volume survived down, so the database is already initialised and init scripts are skipped.
Postgres only reads .sql files at image build time.

A migrate service runs schema migrations and exits. You want api to start only after Postgres is healthy and the migration succeeded. Which depends_on for api is right?

db with condition: service_healthy, and migrate with condition: service_completed_successfully.
db and migrate in the short list form.
migrate with condition: service_healthy.
db with condition: service_started and restart: true.

Your project .env contains POSTGRES_PASSWORD=devpass. compose.yaml sets POSTGRES_PASSWORD: ${POSTGRES_PASSWORD} under db.environment. You run POSTGRES_PASSWORD=other docker compose up -d on a fresh volume. Which password does Postgres get?

devpass, because .env always wins.
other, because shell environment variables take precedence over .env for interpolation.
Both, joined with a comma.
Neither; Compose errors on conflicting values.

Your teammate’s dev setup bind-mounts the whole project (.:/app) into the API container on macOS. The app fails with a native module error and file changes feel slow. What do you recommend?

Add :ro to the bind mount.
Switch to a named volume for the whole project.
Run npm ci on the Mac before every start.
Use Compose watch to sync ./src into the container and rebuild on lockfile changes, leaving node_modules inside the image.

5 questions unanswered