How to communicate between two containers using docker

Question

I'm facing an issue to access one container route in another container. For example i have two micro services called user-service and api-gateway . I'm trying to access user-service route in api-gateway .

My api-gateway file could be like below

  const userServiceProxy = httpProxy(http://localhost:8093);
  this.app.post('/admin/register', async(req, res) => {

      userServiceProxy(req, res);

  });

api-gateway is running on port 8080

My user-service file could be like below

 app.post('/admin/register', function (req, res) {
  res.send('POST request')
 })

when i access route through api-gateway with the port 8080 i couldn't able to call the route but when i tried to access with the port 8093 i can able to see the result.

My docker-compose file could be like below

 version: '3'
 services:
   api-gateway:
     container_name: api-gateway
     build: './api-gateway'
     ports:
       - "8080:8080"
     links:
       - user-service
   user-service:
     build: ./user-service
     container_name: user-service
     ports:
     - "8093:8093"

Any help would be greatly appreciated, Thanks in advance!

Answer 1

localhost refers to the localhost inside the container, not the host system.

Use Docker Networks and replace localhost with the service name like api-gateway .

If the containers are in the same network the address http://api-gateway:8093 should work.

Another way is to run the Container on network mode host . This is less isolation but then the address localhost works because the container is now running on the interface of the docker deamon

Answer 2

just add a network specification to you docker-compose file to use a custom bridge network.

something like that might work for you

version: '3'
services:
  api-gateway:
    container_name: api-gateway
    build: './api-gateway'
    ports:
    - "8080:8080"
    networks:
    - mynet
  user-service:
    build: ./user-service
    container_name: user-service
    ports:
    - "8093:8093"
    networks:
    - mynet

networks:
  mynet:
    driver: bridge
    ipam:
      driver: default

according to your specified ports and services in your docker-compose the following connections are now possible:

• api-gateway container: user-service:8093
• user-service container: api-gateway:8080

if i get it right, your api-gateway would now be:

const userServiceProxy = httpProxy(http://user-service:8093);
  this.app.post('/admin/register', async(req, res) => {
      userServiceProxy(req, res);
  });

inside a docker network you can access the ports from other containers directly (no need to specify a port-mapping to your host). probably one of your port-mappings is therefore unnecessary. if you are accessing the user-service only via api-gateway and not directly you may remove the port specification in your docker-compose files (user-service block). your user-service would then be accessible only using the api-gateway. which is probably what you want.

Answer 3

There is also a less known option to connect two or more containers together:

version: '3'

services:
  test1:
    image: alpine
    command: nc -lp 1337
  test2:
    image: alpine
    command: nc -lp 1337
    network_mode: service:test1

This is similar to internal networking of Kubernetes pods - containers linked this way share the same internal adress (the published ports are visible on localhost and can collide with each other). As a result the above config won't work as there will be a port collision:

➜  docker-pod-test docker-compose up
Creating docker-pod-test_test1_1 ... done
Creating docker-pod-test_test2_1 ... done
Attaching to docker-pod-test_test1_1, docker-pod-test_test2_1
test2_1  | nc: bind: Address in use
docker-pod-test_test2_1 exited with code 1

Answer 4

The simplest way would be to use docker flag --net=host this way your docker container would be using your host machine's network instead of their own namespaced networks. eg

docker run -d --network host -p 80:80 nginx

and you can check on http://localhost for nginx welcome page.