A brief discussion on docker-compose network settings

Networks usage tutorial

Official website docker-compose.yml reference document: Compose file version 3 reference

More accurate Chinese translation: Compose file version 3 reference

Networks are usually used for cluster services, so that different applications can run in the same network, thus solving the network isolation problem. This application is very common in swarm deployment. However, this article does not discuss this.

Generally, for cluster services, docker-compose.yml documents are often used to quickly orchestrate and deploy application services. The official website provides the following usage scenarios and methods:

1. docker-compose.yml without explicit network declaration

For example, create docker-compose.yml in the app directory with the following content:

version: '3'
services:
 web:
  mage: nginx:latest
  container_name: web
  depends_on:
   -db
  ports:
   - "9090:80"
  links:
   -db
 db:
  image: mysql
  container_name: db1234567891011121314

After starting the containers using docker-compose up , these containers will be added to the app_default network. Use docker network ls to view the network list and docker network inspect <container id> to view the configuration of the corresponding network.

$ docker network ls
NETWORK ID NAME DRIVER SCOPE
6f5d9bc0b0a0 app_default bridge local
0fb4027b4f6d bridge bridge local
567f333b9de8 docker-compose_default bridge local
bb346324162a host host local
a4de711f6915 mysql_app bridge local
f6c79184ed27 mysql_default bridge local
6358d9d60e8a none null local
12345678910

2. The networks keyword specifies a custom network

For example, the following docker-compose.yml file defines the front and back networks and implements network isolation. The proxy and db can only communicate through the app. Among them, custom-driver-1 cannot be used directly. You should replace it with one of the options such as host, bridge, overlay , etc.

version: '3'

services:
 proxy:
  build: ./proxy
  networks:
   - front
 app:
  build: ./app
  networks:
   - front
   - back
 db:
  image: postgres
  networks:
   - back

networks:
 front:
  # Use a custom driver
  driver: custom-driver-1
 back:
  # Use a custom driver which takes special options
  driver: custom-driver-2
  driver_opts:
   foo: "1"
   bar: "2"123456789101112131415161718192021222324252627

It is worth noting that two networks, back and front, are defined here. It seems that their names are defined as back and font, but you cannot find them using the docker network ls command. If you run the docker-compose up command in myApp directory, the two networks should correspond to myApp_back and myApp_front respectively.

3. Configure the default network

version: '2'

services:
 web:
  build: .
  ports:
   - "8000:8000"
 db:
  image: postgres

networks:
 default:
  # Use a custom driver
  driver: custom-driver-11234567891011121314

4. Use an existing network

networks:
 default:
  external:
   name: my-pre-existing-network1234

Problems encountered

After learning the above, the author is ready to put his own project into practice. My project contains two docker-compose.yml files and uses the links option, so I have to use the networks configuration.

Among them, a docker-compose.yml is used to start the mysql service, located in mysql/ directory:

 version: "3"
services:
 dbmaster:
  image: master/mysql:latest
  container_name: dbmaster
  ports:
   - "3308:3306"
  volumes:
   - $HOME/Work/data/dbmaster:/var/lib/mysql
  environment:
   MYSQL_ROOT_PASSWORD: master
  logging:
   driver: "json-file"
   options:
    max-size: "1000k"
    max-file: "20"
  networks:
   - app

 dbslave:
  image: slave/mysql:latest
  container_name: dbslave
  ports:
   - "3309:3306"
  depends_on:
   -dbmaster
  volumes:
   - $HOME/Work/data/dbslave:/var/lib/mysql
  environment:
   MYSQL_ROOT_PASSWORD: slave
  logging:
   driver: "json-file"
   options:
    max-size: "1000k"
    max-file: "20"
  links:
   -dbmaster
  networks:
   - app
networks:
  default:
  external:
   name: app12345678910111213141516171819202122232425262728293031323334353637383940414243

Another docker-compose.yml is used to start the service program, located in cloudgo/ directory:

version: "3"
services:
 web:
  image: nginx:latest
  container_name: web
  depends_on:
   -cloudgo
  ports:
   - "9090:80"
  volumes:
   - $HOME/Work/docker/docker-compose/nginx/conf.d:/etc/nginx/conf.d
  links:
   -cloudgot
  logging:
   driver: "json-file"
   options:
    max-size: "1000k"
    max-file: "20"
  networks:
   - app

 cloudgo:
  image: cloudgo:latest
  container_name: cloudgo
  ports:
   - "8080:8080"
  logging:
   driver: "json-file"
   options:
    max-size: "1000k"
    max-file: "20" 
  external_links:
   -dbmaster
   -dbslave
  networks:
   - app
networks:
 app:
  external: true123456789101112131415161718192021222324252627282930313233343536373839

I decided to use a pre-created network and then join them to this already created network to enable communication. To do this, I ran the following command:

$ docker network create app1

After that, start running the prepared docker-compose.yml file. First run the configuration file to start mysql, the result is as follows:

$ docker-compose up
ERROR: Service "dbmaster" uses an undefined network "app"12

It has been created, but it still reports an error saying that the network is undefined. I tried changing the name to mysql_app, but the same error message still appears. It was ultimately proven that this approach was not feasible, and no examples were found in official documentation to date.

Therefore, it was finally decided to change the networks configuration in the first docker-compose.yml file to the following:

networks:
  mysql_app:
   driver: bridge123

Define a network in this file for later use. The modification is complete here, and the same modification needs to be made in other places in the file where the network is referenced. Likewise, the same goes for the second file.

Other usages

Use aliases instead of links

The general usage format is as follows:

services:
 some-service:
  networks:
   some-network:
    aliases:
     -alias1
     -alias3
   other-network:
    aliases:
     -alias212345678910

In the following example, my web container can directly access the db container through database:3306 or db:3306 . They belong to the same network and db has a host alias set, so this access method is completely possible.

version: '2'

services:
 web:
  depends_on:
   - worker
  networks:
   - new

 worker:
  depends_on:
   -db
  networks:
   - legacy

 db:
  image: mysql
  networks:
   new:
    aliases:
     - database
   legacy:
    aliases:
     -mysql
networks:
 new:
 legacy:123456789101112131415161718192021222324252627

At this time, directly using depends_on no longer requires link. If the worker needs to access the db, it can directly use mysql:port.

The key points of using networks are:
1. Be careful about how you customize your network
2. Note the relationship between the location of the docker-compose.yml file and the default naming of the network
3. Pay attention to trying several alternative ways to solve problems

The above is the full content of this article. I hope it will be helpful for everyone’s study. I also hope that everyone will support 123WORDPRESS.COM.