docker-compose for services in Spring Boot - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to specify the Docker image for the service.

Spring Boot

services:
  app:
    image: [1]

Drag options to blanks, or click blank then click option'

Abuild

Bdockerfile

Cmy-springboot-app:latest

Dcontainer_name

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'build' or 'dockerfile' instead of 'image' to specify the image name.

Leaving the image name empty or incorrect.

The image key specifies the Docker image to use for the service.

2fill in blank

medium

Complete the code to expose port 8080 from the container to the host.

Spring Boot

services:
  app:
    ports:
      - "[1]:8080"

Drag options to blanks, or click blank then click option'

A80

B443

C3000

D8080

Attempts:

3 left

💡 Hint

Common Mistakes

Using a port different from 8080 on the container side.

Swapping the ports in the mapping.

The format hostPort:containerPort maps the container's port 8080 to the host's port 8080.

3fill in blank

hard

Fix the error in the volume mapping to persist data.

Spring Boot

services:
  db:
    volumes:
      - [1]:/var/lib/postgresql/data

Drag options to blanks, or click blank then click option'

A/var/data

B./data

Cdata

D/data

Attempts:

3 left

💡 Hint

Common Mistakes

Using just 'data' without './' which Docker Compose treats differently.

Using an absolute path that does not exist on the host.

Using ./data maps a local folder to the container's data folder, persisting data.

4fill in blank

hard

Fill both blanks to define environment variables for the database service.

Spring Boot

services:
  db:
    environment:
      - [1]=postgres
      - [2]=password123

Drag options to blanks, or click blank then click option'

APOSTGRES_USER

BPOSTGRES_PASSWORD

CDB_USER

DDB_PASS

Attempts:

3 left

💡 Hint

Common Mistakes

Using custom variable names instead of the expected ones.

Swapping user and password variable names.

These are the standard environment variables for PostgreSQL Docker images.

5fill in blank

hard

Fill all three blanks to define a build context, Dockerfile, and container name for the app service.

Spring Boot

services:
  app:
    build:
      context: [1]
      dockerfile: [2]
    container_name: [3]

Drag options to blanks, or click blank then click option'

A./app

BDockerfile

Cspringboot_app

D./src

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong folder paths for context.

Using incorrect Dockerfile names.

Not naming the container or using invalid names.

The context is the folder with the Dockerfile, dockerfile is the filename, and container_name names the container.

Practice

1. What is the main purpose of using docker-compose with Spring Boot services?

easy

A. To run multiple related services together with one configuration file

B. To compile Java code faster

C. To replace the Spring Boot framework

D. To write unit tests automatically

Solution

1. Step 1: Understand what docker-compose does

   Docker Compose is a tool to run multiple containers (services) together using one YAML file.

2. Step 2: Relate to Spring Boot services

   It helps run your Spring Boot app alongside databases or other services easily.

3. Final Answer:

   To run multiple related services together with one configuration file -> Option A

4. Quick Check:

   docker-compose = run multiple services [OK]

Hint: Remember: docker-compose manages multiple containers easily [OK]

Common Mistakes:

• Thinking docker-compose compiles code
• Confusing docker-compose with testing tools
• Believing it replaces Spring Boot

2. Which of the following is the correct way to specify a service's port mapping in a docker-compose.yml file?

easy

A. ports: - "8080:8080"

B. ports: 8080:8080

C. port: 8080->8080

D. expose: 8080:8080

Solution

1. Step 1: Recall docker-compose port syntax

   Ports are listed as a YAML array with dash and quotes, like ports: - "hostPort:containerPort".

2. Step 2: Check options

   ports: - "8080:8080" matches the correct YAML syntax for port mapping.

3. Final Answer:

   ports: - "8080:8080" -> Option A

4. Quick Check:

   Port mapping uses dash and quotes in YAML [OK]

Hint: Use dash and quotes for ports in docker-compose YAML [OK]

Common Mistakes:

• Omitting dash for list items
• Using wrong key 'port' instead of 'ports'
• Confusing 'expose' with 'ports'

3. Given this docker-compose.yml snippet:

services:
  app:
    image: springboot-app
    ports:
      - "8080:8080"
    depends_on:
      - db
  db:
    image: postgres
    environment:
      POSTGRES_PASSWORD: example

What happens when you run docker-compose up?

medium

A. docker-compose throws a syntax error

B. Only app service starts, db is ignored

C. db starts but app fails due to missing environment

D. Both app and db services start, app waits for db to start

Solution

1. Step 1: Understand depends_on behavior

   The app service depends on db, so docker-compose starts db first, then app.

2. Step 2: Check environment and ports

   db has required environment variable, app exposes port 8080 correctly.

3. Final Answer:

   Both app and db services start, app waits for db to start -> Option D

4. Quick Check:

   depends_on starts dependencies first [OK]

Hint: depends_on starts services in order, no syntax errors here [OK]

Common Mistakes:

• Assuming depends_on waits for full readiness
• Thinking db is ignored without explicit start
• Confusing environment variables with ports

4. You wrote this docker-compose.yml but your Spring Boot app fails to connect to the database:

services:
  app:
    image: springboot-app
    ports:
      - "8080:8080"
    environment:
      SPRING_DATASOURCE_URL: jdbc:postgresql://localhost:5432/mydb
  db:
    image: postgres
    environment:
      POSTGRES_PASSWORD: example

What is the likely problem?

medium

A. POSTGRES_PASSWORD is incorrect environment variable

B. Missing port mapping for db service

C. The app tries to connect to localhost instead of the db service hostname

D. The app image name is wrong

Solution

1. Step 1: Check datasource URL in app environment

   The app uses jdbc URL with 'localhost', which inside container means itself, not db service.

2. Step 2: Understand docker-compose networking

   Services communicate by service name, so URL should use 'db' hostname, not 'localhost'.

3. Final Answer:

   The app tries to connect to localhost instead of the db service hostname -> Option C

4. Quick Check:

   Use service name, not localhost, for inter-service DB URL [OK]

Hint: Use service names, not localhost, inside docker-compose networks [OK]

Common Mistakes:

• Assuming localhost works inside containers
• Forgetting to map ports for external access
• Misnaming environment variables

5. You want to run a Spring Boot app with a MySQL database using docker-compose. You want the database to keep data even if the container stops. Which snippet correctly adds persistent storage for the database?

hard

A. volumes:
- /var/lib/mysql:/db-data

volumes:
db-data:

B. volumes:
- db-data:/var/lib/mysql

volumes:
db-data:

C. volumes:
- db-data:/mysql/data

volumes:
mysql-data:

D. volumes:
- /mysql/data:/db-data

volumes:
db-data:

Solution

1. Step 1: Understand volume syntax for persistence

   Docker volumes map a named volume to the container path where data is stored, e.g., db-data:/var/lib/mysql.

2. Step 2: Check volume declaration

   The named volume must be declared under top-level volumes: with the same name.

3. Final Answer:

   volumes: - db-data:/var/lib/mysql volumes: db-data: -> Option B

4. Quick Check:

   Named volume mapped to container path with declaration [OK]

Hint: Map named volume to container data path and declare it below [OK]

Common Mistakes:

• Reversing host and container paths
• Not declaring the named volume
• Using wrong container data directory