spring boot - Docker: Springboot container can not connect to PostgreSql Container Connection error

Question

I am building my first Springboot 2.0 application. I am trying to put my Springboot application into one docker container and my PostgresDB into another container.

My Dockerfile

    FROM frolvlad/alpine-oraclejdk8:slim
    VOLUME /tmp
    ADD springboot-api-demo-0.1*.jar app.jar
    RUN sh -c 'touch /app.jar'
    EXPOSE 9443
    ENTRYPOINT [ "sh", "-c", "java $JAVA_OPTS -Djava.security.egd=file:/dev/urandom -jar /app.jar" ]

My docker-compose.yml file

version: "2.1"

services:
  springboot-api-demo:
    image: "fw/springboot-api-demo"
    mem_limit: 1024m
    ports:
      - "8080:8080"
    environment:
      - SPRING_PROFILES_ACTIVE=local
      - AWS_REGION=local
      - ENVIRONMENT=local
      - AUTH_ENABLED=false
  postgres:
    container_name: pgdb
    image: postgres:9.6-alpine
    environment:
    - 'POSTGRES_ROOT_PASSWORD=postgres'
    - 'POSTGRES_USER=postgres'
    - 'POSTGRES_PASSWORD=postgres'
    ports:
    - "54321:5432"

I am using Springboot JPA Data 2.0 with below config data in my application.properties

spring.datasource.url= jdbc:postgresql://localhost:54321/java_learning
spring.datasource.username=postgres
spring.datasource.password=postgres

I can test that Both of the Images are up. Also from docker log and docker events, I see that postgres Container is running fine, even I can access it and also created a DB too. But springboot container started but i died because it could not connect to postgress and throwing error below.

Unable to obtain connection from database: The connection attempt failed

Note that my host machine already has Postgres on port 5432 thats why I did a port mapping ofr 54321:5432 on my postgres container. Here is Proof :) -

?  springboot-api-demo git:(master) ? lsof -i:54321              
COMMAND     PID             USER   FD   TYPE             DEVICE SIZE/OFF NODE NAME
com.docke 44345 shailendra.singh   18u  IPv4 0xf62897fbdd69e31d      0t0  TCP *:54321 (LISTEN)
com.docke 44345 shailendra.singh   21u  IPv6 0xf62897fbdd119975      0t0  TCP localhost:54321 (LISTEN)

?  springboot-api-demo git:(master) ? lsof -i:5432 
COMMAND  PID             USER   FD   TYPE             DEVICE SIZE/OFF NODE NAME
postgres 715 shailendra.singh    5u  IPv6 0xf62897fbb43e03b5      0t0  TCP localhost:postgresql (LISTEN)
postgres 715 shailendra.singh    6u  IPv4 0xf62897fbbaeea9bd      0t0  TCP localhost:postgresql (LISTEN)

I am not sure what is the problem. But my Springboot application is not able to connect my postgres container which is running fine with proper creadentials.

Answer 1

Try with :

spring.datasource.url= jdbc:postgresql://pgdb:5432/java_learning

The postgres database is not running on localhost, it's running in the other container which has an other IP (yet unknown).

Thanksfully, docker-compose automatically create a network shared among all the containers in the docker-compose.yml (unless explicitly said to do not), as a result you can magically use the service name as an hostname.

Also, you have a typo in the port, Postgres use 5432 by default, not 54321