docker-compose for services in Spring Boot - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when you run this docker-compose.yml?

Given this docker-compose.yml file for two Spring Boot services, what will be the result after running docker-compose up?

version: '3.8'
services:
  app1:
    image: springboot-app1:latest
    ports:
      - "8080:8080"
  app2:
    image: springboot-app2:latest
    ports:
      - "8081:8080"
    depends_on:
      - app1

Spring Boot

version: '3.8'
services:
  app1:
    image: springboot-app1:latest
    ports:
      - "8080:8080"
  app2:
    image: springboot-app2:latest
    ports:
      - "8081:8080"
    depends_on:
      - app1

A Only app2 starts; app1 is ignored because it has no depends_on.

B Both app1 and app2 start; app2 waits for app1 to start before launching.

C Only app1 starts; app2 fails because depends_on is not a valid key.

D Both app1 and app2 start simultaneously without waiting for each other.

💡 Hint

Check what depends_on does in docker-compose.

The depends_on key makes app2 wait for app1 to start before launching. Both services will run, but app2 starts after app1.

📝 Syntax

intermediate

Which docker-compose.yml snippet is valid for linking two Spring Boot services?

Choose the valid docker-compose.yml snippet that correctly links serviceA and serviceB so serviceB can access serviceA by hostname.

A

version: '3'
services:
  serviceA:
    image: springboot-a
  serviceB:
    image: springboot-b
    depends_on:
      - serviceA

B

version: '3'
services:
  serviceA:
    image: springboot-a
  serviceB:
    image: springboot-b
    depends_on:
      - serviceA
    links:
      - serviceA

C

version: '3'
services:
  serviceA:
    image: springboot-a
  serviceB:
    image: springboot-b
    links:
      - serviceA

D

version: '3'
services:
  serviceA:
    image: springboot-a
  serviceB:
    image: springboot-b
    network_mode: service:serviceA

💡 Hint

Remember that links is deprecated but still valid in version 3 for hostname resolution.

Option C uses links correctly to allow serviceB to access serviceA by hostname. Option C mixes depends_on and links unnecessarily. Option C lacks links so hostname access is not guaranteed. Option C uses an invalid network_mode value.

❓ state_output

advanced

What is the exposed port of app2 in this docker-compose setup?

Given this docker-compose.yml, what port on the host machine will map to app2's internal port 8080?

version: '3.8'
services:
  app1:
    image: springboot-app1
    ports:
      - "8080:8080"
  app2:
    image: springboot-app2
    ports:
      - "9090:8080"

Spring Boot

version: '3.8'
services:
  app1:
    image: springboot-app1
    ports:
      - "8080:8080"
  app2:
    image: springboot-app2
    ports:
      - "9090:8080"

A 8080 and 9090

B 8080

C 8081

D 9090

💡 Hint

Look at the port mapping format: hostPort:containerPort.

The port mapping "9090:8080" means the container's port 8080 is exposed on host port 9090.

🔧 Debug

advanced

Why does app2 fail to connect to app1 in this docker-compose setup?

Consider this docker-compose.yml snippet:

version: '3.8'
services:
  app1:
    image: springboot-app1
    ports:
      - "8080:8080"
  app2:
    image: springboot-app2
    ports:
      - "8081:8080"

App2 tries to connect to app1 using localhost:8080 but fails. Why?

Spring Boot

version: '3.8'
services:
  app1:
    image: springboot-app1
    ports:
      - "8080:8080"
  app2:
    image: springboot-app2
    ports:
      - "8081:8080"

A Because app2's localhost refers to itself, not app1; it should use the service name 'app1' instead.

B Because the ports are mapped incorrectly; app1 should expose 8081 instead of 8080.

C Because app2 needs a depends_on key to start after app1.

D Because docker-compose does not support multiple services communicating.

💡 Hint

Remember how Docker networking works between containers.

Each container has its own localhost. To connect between containers, use the service name as hostname, not localhost.

🧠 Conceptual

expert

What is the effect of adding 'restart: always' to a service in docker-compose?

In a docker-compose.yml file for Spring Boot services, what does adding restart: always do?

A It makes the service restart automatically if it stops or the Docker daemon restarts.

B It forces the service to restart every 5 minutes regardless of status.

C It disables manual stopping of the service via docker-compose commands.

D It restarts the service only if the container exits with an error code.

💡 Hint

Check the official Docker Compose restart policies.

restart: always ensures the container restarts automatically if it stops for any reason or if Docker restarts.