Failed to connect to mongodb with docker-compose

Question

I have a web server written in java that connect to mongo db

my docker-compose file is:

version: "3.2"

services:

  web:
    image: org/web-server:latest
    restart: always
    env_file: .env
    depends_on: 
      - mongo
    ports:     
     - "8080:9999"
    networks:
      - web-network
  mongo:
    image: mongo
    restart: always
    ports:
      - 27017:27017
    networks: 
      - web-network
    volumes: 
      - "mongodbdata:/data/db"

networks:
    web-network:
volumes: 
    mongodbdata:

Exception is:

org.mongodb.driver.cluster - Exception in monitor thread while connecting to server localhost:27017
bot_1    | com.mongodb.MongoSocketOpenException: Exception opening socket
bot_1    |  at com.mongodb.internal.connection.AsynchronousSocketChannelStream$OpenCompletionHandler.failed(AsynchronousSocketChannelStream.java:124)
bot_1    |  at sun.nio.ch.Invoker.invokeUnchecked(Invoker.java:128)
bot_1    |  at sun.nio.ch.Invoker$2.run(Invoker.java:218)
bot_1    |  at sun.nio.ch.AsynchronousChannelGroupImpl$1.run(AsynchronousChannelGroupImpl.java:112)
bot_1    |  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
bot_1    |  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
bot_1    |  at java.lang.Thread.run(Thread.java:748)
bot_1    | Caused by: java.net.ConnectException: Connection refused
bot_1    |  at sun.nio.ch.UnixAsynchronousSocketChannelImpl.checkConnect(Native Method)
bot_1    |  at sun.nio.ch.UnixAsynchronousSocketChannelImpl.finishConnect(UnixAsynchronousSocketChannelImpl.java:252)
bot_1    |  at sun.nio.ch.UnixAsynchronousSocketChannelImpl.finish(UnixAsynchronousSocketChannelImpl.java:198)
bot_1    |  at sun.nio.ch.UnixAsynchronousSocketChannelImpl.onEvent(UnixAsynchronousSocketChannelImpl.java:213)
bot_1    |  at sun.nio.ch.EPollPort$EventHandlerTask.run(EPollPort.java:293)
bot_1    |  ... 1 common frames omitted

Answer 1

When you try to connect to mongo with mongodb://localhost:27017 your application look for local container which is the one that host only the app name web in docker compose

The easiest way to solve this problem is to set your uri to mongodb://mongo:27017 But if you like you use mongodb://localhost:27017 you should use Link option in docker compose.

For more info look at this doc: https://docs.docker.com/compose/networking/#links