Docker Compose for local development in Microservices - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Architecture

intermediate

Designing a Docker Compose setup for a multi-service app

You have three microservices: a frontend, a backend API, and a database. You want to run them locally using Docker Compose. Which of the following docker-compose.yml snippets correctly defines the services with proper network and volume setup for local development?

A

version: '3'
services:
  frontend:
    build: ./frontend
    ports:
      - '3000:3000'
    depends_on:
      - backend
  backend:
    build: ./backend
    ports:
      - '8000:8000'
    environment:
      - DATABASE_URL=postgres://user:pass@db:5432/app
    depends_on:
      - db
  db:
    image: postgres:15
    volumes:
      - db-data:/var/lib/postgresql/data
volumes:
  db-data: {}

B

version: '2'
services:
  frontend:
    image: node:latest
    ports:
      - '3000:3000'
  backend:
    image: python:3.9
    ports:
      - '8000:8000'
  db:
    image: postgres:latest
    volumes:
      - ./data:/var/lib/postgresql/data

C

version: '3.8'
services:
  frontend:
    build: ./frontend
    ports:
      - '3000:3000'
  backend:
    build: ./backend
    ports:
      - '8000:8000'
    environment:
      DATABASE_URL: postgres://user:pass@localhost:5432/app
  db:
    image: postgres:15
    volumes:
      - db-data:/var/lib/postgresql/data
volumes:
  db-data: {}

D

version: '3'
services:
  frontend:
    build: ./frontend
    ports:
      - '3000:3000'
    depends_on:
      - backend
  backend:
    build: ./backend
    ports:
      - '8000:8000'
    environment:
      - DATABASE_URL=postgres://user:pass@localhost:5432/app
    depends_on:
      - db
  db:
    image: postgres:15
    volumes:
      - db-data:/var/lib/postgresql/data
volumes:
  db-data: {}

💡 Hint

Check how services communicate using service names and how volumes are defined for persistent data.

Option A correctly uses service names for database connection (db), defines volumes for data persistence, and sets dependencies so services start in order. Options C and D incorrectly use localhost in the backend environment, which won't resolve inside Docker network. Option A uses version 2 and lacks proper build context and network setup.

❓ scaling

intermediate

Scaling services with Docker Compose

You want to test how your backend service handles multiple instances locally using Docker Compose. Which command correctly scales the backend service to 3 instances?

A docker-compose up --scale backend=3

B docker-compose scale backend=3

C docker-compose run --scale backend=3

D docker-compose up -d backend=3

💡 Hint

Remember the modern syntax for scaling services with docker-compose up.

The correct command is docker-compose up --scale backend=3. The scale command is deprecated. The run command does not support scaling.

❓ tradeoff

advanced

Tradeoffs of using Docker Compose for local development

Which of the following is a common tradeoff when using Docker Compose for local development of microservices?

A It guarantees identical performance and behavior as production environments.

B It simplifies environment setup but may not perfectly mimic production networking and scaling.

C It eliminates the need for any configuration files or environment variables.

D It automatically scales services to production-level traffic without manual setup.

💡 Hint

Think about differences between local and production environments.

Docker Compose is great for local setups but does not fully replicate production environments, especially in networking and scaling. It requires configuration files and environment variables. Scaling is manual and limited.

🧠 Conceptual

advanced

Understanding service dependencies in Docker Compose

In Docker Compose, what does the depends_on key do when defined between services?

A It guarantees the dependent service is fully ready and healthy before starting the current service.

B It automatically restarts the dependent service if the current service fails.

C It ensures the dependent service starts before the current service but does not wait for it to be ready.

D It links the dependent service's ports to the current service.

💡 Hint

Consider what depends_on controls in startup order versus readiness.

The depends_on key controls startup order but does not wait for the dependent service to be fully ready or healthy. Health checks require additional configuration.

❓ estimation

expert

Estimating resource usage for Docker Compose local setup

You plan to run 5 microservices locally with Docker Compose. Each service requires approximately 500MB RAM and 0.5 CPU cores. Your laptop has 8 CPU cores and 16GB RAM. Considering Docker and OS overhead, what is the maximum number of service instances you can run simultaneously without swapping or CPU throttling?

A 24 instances (limited by RAM: 16GB / 0.5GB = 32, CPU limits to 8 cores * 3 instances)

B 10 instances (limited by RAM: 16GB / 0.5GB = 32 but CPU limits to 8 cores * 1 instance each)

C 28 instances (16GB / 0.5GB = 32 RAM, 8 cores * 3.5 instances per core CPU)

D 16 instances (8 cores * 2 per core, RAM is sufficient)

💡 Hint

Calculate max instances by RAM and CPU separately, then take the smaller number.

RAM allows 32 instances (16GB / 0.5GB). CPU allows 16 instances (8 cores * 2 instances per core). Considering overhead, the limiting factor is CPU, so max is 16 instances.