[Solved] 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:... | Spring Boot

Spring Boot - Docker and Deployment

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?

APOSTGRES_PASSWORD is incorrect environment variable

BMissing port mapping for db service

CThe app tries to connect to localhost instead of the db service hostname

DThe app image name is wrong

Step-by-Step Solution

Solution:

Step 1: Check datasource URL in app environment
The app uses jdbc URL with 'localhost', which inside container means itself, not db service.
Step 2: Understand docker-compose networking
Services communicate by service name, so URL should use 'db' hostname, not 'localhost'.
Final Answer:
The app tries to connect to localhost instead of the db service hostname -> Option C
Quick Check:
Use service name, not localhost, for inter-service DB URL [OK]

Quick Trick: 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

Master "Docker and Deployment" in Spring Boot

9 interactive learning modes - each teaches the same concept differently

Learn Why Deep Visual Try Challenge Project Recall Perf

More Spring Boot Quizzes

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

Step 1: Check datasource URL in app environment

Step 2: Understand docker-compose networking

Final Answer:

Quick Check:

Want More Practice?