How to connect to a Docker Compose container from a standalone container

Question

I'm using a Docker Compose file to spin up a version of fluentd as follows:

version: '3'
services:

  fluentd:
    image: "fluent/fluentd:latest"
    ports:
      - "9880:9880"
      - "24224:24224"
    volumes:
      - ./config:/fluentd/etc
      - ./data/fluentd/logs:/fluentd/logs
    environment:
      - FLUENTD_CONF=fluentd.conf

This launches a network called project_default and then launches fluentd.

I then want to connect to that fluentd instance from a vanilla Docker container containing an application that I'm currently developing. As far as I can tell from the documentation I should be able to run the container and connect to the fluentd instance using the following command:

docker run --network=project_default -e FLUENTHOST='fluentd' myapp:1.0.0

where the FLUENTHOST environment variable passes the host name that fluentd should be running on.

When I run this I get a "lookup 'fluentd': no such host" error message.

Am I missing a step in either my Docker Compose file or my docker run command?

Answer 1

In your docker-compose file, you need to specify custom netwok driver bridge.

networks:
    your_network_name:
      driver: bridge

and then run your another container by using --network="your_network_name" flag

I am having similar kind of approach but I am running both containers by different docker-compose file, have a look.

docker-compose file to run Container 1 on custom network name code-network

version: '2'
services:

 container_1:
  build: container_1
  networks:
   - code-network

networks:
 code-network:
  driver: bridge

docker-compose file to run Container 2 to run on already existing network code-network

version: '2'
services:

 container_2:
  build: "container_2"   
  networks:
    - code-network

networks:
  code-network:
   external: true

With above both container 1 and container 2 are running on same network, hope this will help you :)