How docker implements cross-host communication

Docker is one of the most popular containerization technologies currently, which provides a lightweight way to package and deploy applications. In practical applications, it is often necessary to migrate containers between multiple hosts to improve application reliability and scalability. However, since each host has its own network environment, cross-host communication is a common problem. This article will introduce how to use Docker to achieve cross-host communication.

1. Docker network model

Docker’s network model includes three network driver types: bridge, host and overlay. Among them, bridge is the most common one, which allows Docker containers and hosts to share a single network. However, if you want to communicate across hosts, you need to expose the container through network port mapping. The host mode uses the host network directly, which can avoid the overhead of port mapping, but the network isolation between containers becomes worse. The overlay mode is used to implement distributed networks and can communicate across multiple Docker hosts.

2. Docker cross-host communication solution

1. Using the bridge network driver

When using the bridge network driver, you need to use port mapping to achieve cross-host communication Host communication, the specific steps are as follows:

Step 1: Run the container on the first host and expose the port to be used.

$ docker run -d --name container -p 8080:80 nginx

In the above command, we started a container named container and mapped container port 80 to host port 8080.

Step 2: On the second host, use curl to test that you can access the port exposed by the container.

$ curl http://<第一台主机IP地址>:8080

In the above command, we use the curl tool to make a request to the 8080 port of the first host and obtain the default welcome interface of the Nginx server.

2. Using the overlay network driver

Using the overlay network driver, you can directly connect containers from multiple Docker hosts. The specific steps are as follows:

Step 1: Enable the overlay network on each host in the cluster.

$ docker network create -d overlay my-overlay-network

In the above command, we created an overlay network named my-overlay-network on each host.

Step 2: Run the web service in the container and use the overlay network connection.

$ docker run -d --name web --network=my-overlay-network nginx

In the above command, we started a container named web and connected it to the my-overlay-network network.

Step 3: On other hosts, use curl to test that you can access the web service.

$ curl http://web

In the above command, we use the curl tool to make a request to the web host and obtain the default welcome interface of the Nginx server.

3. Summary

Containerization technology has become one of the standard ways to develop and deploy applications in modern times. Using Docker to achieve cross-host communication is a problem often encountered in this process. Through this article, we learned about the solution of using bridge and overlay network drivers to achieve cross-host communication. Among them, the overlay network driver has better scalability and is suitable for implementing distributed applications.

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