I've got a Docker image which accepts a DATABASE_URL env and start the container with

docker run -p 3000:3000 -e DATABASE_URL=mysql://root:foobar@localhost:3309/app app_image

On startup the container should run migrations on a database bootstraped from a docker-compose.yml file:

version: '3'

services:
  database:
    image: mysql:8.0
    environment:
      - MYSQL_DATABASE=app
      - MYSQL_ROOT_PASSWORD=foobar
    ports:
      - "3309:3306"
    volumes:
      - db:/var/lib/mysql

  volumes:
    db:

Unfortunately, I always get Can't reach database at localhost:3309. I assume it has something to do with the network settings - but how to configure these settings in order to make it work?

I've tried many different configurations (e.g. database, 127.0.0.1, etc. instead of localhost) but couldn't make it work and I'm honestly running out of ideas.

Thanks!

CodePudding user response：

Some clarifications: Unless you specifically bind containers to the same host e.g. --network host or link them together in docker compose using links Links documentation, container A will not be able to reach anything on container B via localhost.

Docker compose, unless specified differently in the docker-compose.yaml file, automatically creates a separate network for all of the containers that are managed by that compose file, its name is usually based on the folder the file is in. You can view it using docker network ls

that means, any container not managed by that compose file, is not part of the same network by default.

One option easy enough option that you have (among many probably):

1. Decide on a network name which the compose file and you container will agree on
2. create this network beforehand (before starting the standalone container and the compose file), the network will probably be in bridge mode docker network docs docker network create -d bridge my-bridge-network
3. add it to the compose file so that docker compose uses it instead of the auto-created one

networks:
  - my-bridge-network

4. when starting the stand-alone container, specify which network to attach it to

docker run -p 3000:3000 -e DATABASE_URL=mysql://root:foobar@database:3309/app --network my-bridge-network app_image

5. notice that the IP/HOSTNAME for the database container is according to the service name in the compose file, you can change that using hostname: some-other-hostname in the yaml.

all containers should now be on the same network, each one has a different IP/Hostname using this method (so cant use localhost for inter-container communication)

Alternative option: use network: host for both the compose file and the stand-alone container, they can talk to each other using localhost. i dont recommend this option, and cant find a good enough reason to use it over other options.