Docker compose

Index

【Concept】

When multiple containers need to communicate or depend on each other, we can arrange them together according to certain rules. This is done by declaring them in a docker-compose.yml file.
The docker-compose.yml is based on version 3. For details on each option, refer to the: v3 configuration reference
Even for a single container, I prefer to write a docker-compose.yml file, as it provides a clearer view of what configurations are made within that container.

Container Shared Network

If containers need to communicate with each other, they must be on the same network configuration (special handling is required in Docker Swarm mode).
Multiple containers on the same network do not need to be orchestrated within a single docker-compose.yml.
Communication between containers can be done via IP:port. Alternatively, containers can communicate using ContainerName:port, but the network orchestration and configuration must be handled carefully to account for differences.

Here is an example using Redis master-slave (multiple Redis instances need to communicate to back up data):

master

version: "3.5"

services:
  redis-master:
    image: redis:latest
    container_name: redis-master
    restart: always
    ports:
      - "6371:6379"
    networks:
      - proxy
    privileged: true # 拥有root权限,可以挂在在其他设备上
    volumes:
      - $PWD/conf/redis.conf:/usr/local/etc/redis/redis.conf:rw
      - $PWD/data:/data:rw
    command: redis-server /usr/local/etc/redis/redis.conf

# 加入已有网络
networks:
  proxy:
    external: true

slave

version: "3.5"

services:
  redis-2:
    image: redis:latest
    container_name: redis-2
    restart: always
    ports:
      - "6372:6379"
    networks:
      - proxy
    volumes:
      - $PWD/conf2/redis.conf:/usr/local/etc/redis/redis.conf:rw
      - $PWD/data2:/data:rw
    command: redis-server /usr/local/etc/redis/redis.conf

  redis-3:
    image: redis:latest
    container_name: redis-3
    restart: always
    ports:
      - "6373:6379"
    networks:
      - proxy
    volumes:
      - $PWD/conf3/redis.conf:/usr/local/etc/redis/redis.conf:rw
      - $PWD/data3:/data:rw
    command: redis-server /usr/local/etc/redis/redis.conf

# 加入已有网络
networks:
  proxy:
    external: true

【Warning】

Looking at the yml file alone doesn't reveal the communication setup; you need to check the corresponding configuration：

Here, pay attention to the slaveof field in the Redis configuration for the slave. You can think about why the port is 6379 instead of 6371 😎

When multiple containers need to share data, it is necessary to mount it to a shared volume, and then specify the volume mapping when orchestrating or starting the containers.
If the data in the shared volume is highly sensitive and important, it is best to perform regular backups.
If multiple containers need to share data, it is recommended to create a shared volume in advance and then specify the usage of the existing shared volume.

version: "3.5"
services:
  web:
    image: alpine
    volumes:
      - mydata:/data
  web1:
    image: alpine
    volumes:
      - mydata:/data
volumes:
  mydata:
  dbdata:

version: "3.5"
  services:
    web:
      image: alpine
      volumes:
        - mydata:/data
    web1:
      image: alpine
      volumes:
        - mydata:/data
volumes:
  mydata:
    external: true

Docker compose

Container Shared Network

Multiple Containers Sharing Files and Directories