Connect Docker Containers

Problem

I needed multiple docker containers to communicate with each other, through network calls.

Solution

Using "BRIDGE & OVERLAY network modes"

Connect Containers in Same Docker Host

Bridge Network Mode - allows containers connected to the same bridge network to communicate, while providing isolation from containers which are not connected to that bridge network.

A default bridge called "bridge" is always created between all the containers in the host.

Connect Containers in Different Docker Host

Overlays Network Mode - this network sits on top of the host-specific networks, allowing containers connected to it to communicate securely when encryption is enabled.

For each container you want to add to the network, add the following in docker-compose file.

networks:
    - local //{network_name}

and at the end of the file, add the following

networks:
local: // {network_name}
    driver: bridge

Finally, docker-compose looks like this

local-redis:
    image: redis
    ports:
        - "6379:6379"
    volumes:
        - redis-data:/data
    networks:
        - local

local-mongo:
    image: mongo:3.2
    command: ["mongod", "--smallfiles"]
    ports:
        - "27017:27017"
    volumes:
        - mongo-data:/data/db
    networks:
        - local
networks:
local:
    driver: bridge

And, this is how you make network calls to call other docker containers

{container_name}:{container_port}

"mongo_url": "mongodb://local-mongo:27017/analytics"

"redis_host": "local-redis"

Side Note

What are Container Port & Host Port?

A Container port is the port to be used within a container, when using BRIDGE or USER networking mode.

A Host port specifies a port on the host machine to bind to.

In a docker-compose file, it looks like this,

local-application:
    image: ...
    ports:
        - "7602:7600" //{hostPort}:{containerPort}

Inside docker code, you can call like this

"app_url": "http://local-application:7600"

Outside docker(from browser), you can call like this

http://localhost:7602/

References

Networking Types

Docker Compose Ports