Connecting to a Mongo container from Spring container

Question

I have a problem here that I really cannot understand. I already saw few topics here with the same problem and those topics was successfully solved. I basically did the same thing and cannot understand what I'm doing wrong.

I have a Spring application container that tries to connect to a Mongo container through the following Docker Composer :

version: '3'
services:
  app:
    build: .
    ports:
      - "8080:8080"
    links:
      - db
      
  db:
    image: mongo
    volumes:
      - ./database:/data
    ports:
      - "27017:27017"

In my application.properties :

spring.data.mongodb.uri=mongodb://db:27017/app

Finally, my Dockerfile :

FROM eclipse-temurin:11-jre-alpine
WORKDIR /home/java
RUN mkdir /home/java/bar
COPY ./build/libs/foo.jar /home/java/bar/foo.jar
CMD ["java","-jar", "/home/java/bar/foo.jar"]

When I run docker compose up --build I got:

2022-11-17 12:08:53.452  INFO 1 --- [null'}-db:27017] org.mongodb.driver.cluster               : Exception in monitor thread while connecting to server db:27017

Caused by: java.net.UnknownHostException: db

Running the docker compose ps I can see the mongo container running well, and I am able to connect to it through Mongo Compass and with this same Spring Application but outside of container. The difference running outside of container is the host from spring.data.mongodb.uri=mongodb://db:27017/app to spring.data.mongodb.uri=mongodb://localhost:27017/app .

Also, I already tried to change the host for localhost inside of the spring container and didnt work.

Answer 1

You need to specify MongoDB host, port and database as different parameters as mentioned here .

spring.data.mongodb.host=db

spring.data.mongodb.port=27017

spring.data.mongodb.authentication-database=admin

As per the official docker-compose documentation the above docker-compose file should worked since both db and app are in the same.network (You can check if they are in different.networks just in case)

If the.networking is not working, as a workaround, instead of using localhost inside the spring container, use the server's IP, ie, mongodb://<server_ip>:27017/app (And make sure there is no firewall blocking it)