I’m trying to connect a spring application to a postgres container using docker compose but I always get this errors:

If I use the container name postgres, this error shows up:

java.net.UnknownHostException: postgres

If I try to use “localhost”, a connection refused shows up:

java.net.ConnectException: Connection refused

What else is missing on my configuration?

These are my spring configs:

spring.datasource.url=jdbc:postgresql://localhost:5432/fastfood
spring.datasource.username=postgres
spring.datasource.password=postgres
spring.datasource.driver-class-name=org.postgresql.Driver
spring.jpa.database-platform=org.hibernate.dialect.PostgreSQLDialect

The docker-compose file:

version: '3.7'

services:
  db:
    image: postgres:16-alpine
    environment:
      POSTGRES_PASSWORD: "postgres"
      POSTGRES_DB: "fastfood"
    ports:
      - "5432:5432"
    networks:
      - postgres
    restart: always
  api:
    build:
      context: .
      dockerfile: Dockerfile
    ports:
      - "8081:8080"
    volumes:
      - .:/app
    depends_on:
      - db

networks:
  postgres:
    driver: bridge

The Dockerfile:

FROM openjdk:21-jdk

VOLUME /tmp

RUN mkdir /work

COPY . /work

WORKDIR /work

RUN chmod +x ./mvnw

RUN ./mvnw clean package

EXPOSE 8080

RUN mv /work/build/libs/*.jar /work/app.jar

ENTRYPOINT ["java", "-jar", "/work/app.jar"]