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DevOps / GitLab CI Basics Interview Questions

What are 'services' in GitLab CI/CD and how do you use them?

Services are Docker containers that run alongside the main job container, providing supporting infrastructure like databases, message brokers, or a Docker daemon. They share a network namespace with the job container.

# Run tests with a PostgreSQL database service:
test-with-db:
  stage: test
  image: python:3.12
  services:
    - postgres:16-alpine          # starts a Postgres container
  variables:
    POSTGRES_DB: testdb
    POSTGRES_USER: postgres
    POSTGRES_PASSWORD: secret
    DATABASE_URL: "postgresql://postgres:secret@postgres/testdb"
  script:
    - pip install -r requirements.txt
    - python -m pytest

# Multiple services:
integration-test:
  image: node:20
  services:
    - redis:7-alpine
    - postgres:16-alpine
    - name: rabbitmq:3-management
      alias: rabbit             # access as "rabbit" hostname
  script:
    - npm test

# Service with alias and entrypoint override:
custom-service:
  services:
    - name: my-registry/my-service:latest
      alias: api-mock
      entrypoint: ["/usr/bin/api-mock"]
      command: ["--port", "8080"]

Services are accessible from the main job container using the service's image name (or alias) as the hostname. For example, a postgres:16 service is reached at hostname postgres. Set an alias when you need a custom hostname.

How do you access a PostgreSQL service container from the main job container in GitLab CI?
What is the purpose of the 'alias' option when defining a service in GitLab CI?

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