How to implement communication between Dockers

In modern software development, Docker has become a very popular virtualization technology, which allows developers to develop, test and deploy in different environments. An important feature of Docker is that it can run on different hosts, so how to implement communication between Dockers in a multi-host environment has become a hot topic.

This article will introduce how to implement communication between different Docker hosts, including:

1. The concepts and characteristics of Docker network;
2. Running on the same host The communication method of Docker containers;
3. The communication method of running Docker containers on different hosts;
4. Use Docker Compose to manage the communication of multiple containers.

1. Concepts and characteristics of Docker network

In Docker, the network is an independent subsystem that provides communication capabilities for different containers. An important feature of the Docker network is to isolate different containers in different networks, and communication between containers must be achieved through the network. Common Docker network types include:

1. bridge mode: Default mode, all containers are connected to the same virtual network.
2. Host mode: Connect the container directly to the physical network of the host, and the containers can communicate through the IP address of the host.
3. Overlay mode: used to create isolated virtual networks between multiple Docker hosts, which can achieve cross-host container communication.

In Docker, communication between different containers can also be achieved through customized networks.

2. Communication method of Docker containers running on the same host

Communication between Docker containers running on the same host is the easiest to achieve. By default, the Docker bridge network allows communication between all containers through its IP address. Therefore, communication between different containers on the same host only needs to be done using the container's IP address.

In Docker, you can use the following command to view the IP address of a running container:

docker inspect -f '{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' <container_name>

The sample code for communication between Docker containers on the same host is as follows:

import requests

response = requests.get('http://<container_ip>:<port>/<api_endpoint>')

3. Communication method of running Docker containers on different hosts

When different Docker containers run on different hosts, they cannot communicate through the IP address of the container because they no longer belong to the same a network. Therefore, other means must be used to communicate between them.

In Docker, container communication on different hosts can be achieved in the following two ways:

1. Use Port Mapping to map the application port to the host port, so that Containers on other hosts can access the container through the host's IP address and port.
2. Use the Overlay network to connect containers on different hosts to the same virtual network so that they can communicate directly through the IP address of the container.

The sample code for using Port Mapping is as follows:

import requests

response = requests.get('http://<host_ip>:<mapped_port>/<api_endpoint>')

When using an Overlay network to connect containers on different hosts, you need to perform the following steps:

1. Enable Swarm mode on all Docker hosts: docker swarm init;
2. Create an Overlay network on a Docker host: docker network create -d overlay <network_name>；
3. Start the container in the Overlay network: docker service create --name <service_name> --network <network_name> <image_name>.

The sample code for mutual communication in the Overlay network is as follows:

import requests

response = requests.get('http://<container_ip>:<port>/<api_endpoint>')

4. Use Docker Compose to manage the communication of multiple containers

Docker Compose is a A tool for managing multiple Docker containers, it can define the startup methods and parameters of multiple containers through YAML files. In Docker Compose, the communication method between containers can be configured in YAML files.

The following is a sample YAML code that uses Docker Compose to manage communication between multiple containers:

version: '3'

services:
  db:
    image: mysql:5.7
    environment:
      MYSQL_DATABASE: 'mydb'
      MYSQL_USER: 'root'
      MYSQL_PASSWORD: 'root'
      MYSQL_ROOT_PASSWORD: 'root'
    volumes:
      - ./db:/var/lib/mysql
    ports:
      - '3306:3306'
    networks:
      - my-network

  web:
    build: .
    ports:
      - "5000:5000"
    volumes:
      - .:/code
    networks:
      - my-network
    depends_on:
      - db

networks:
  my-network:

In the above example, the db container and the network are connected by defining a network named "my-network" The web container is connected to the same virtual network, and Port Mapping is used to map MySQL's 3306 port to the host's 3306 port.

Summary

Through the introduction of this article, you should have mastered the method of communication between different Docker hosts. For container communication on the same host, you only need to use the IP address of the container; for container communication on different hosts, you can use Port Mapping and Overlay networks. In addition, using Docker Compose makes it easier to manage communication between multiple containers.

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