How to solve the problem that docker cannot communicate with host dns

Solutions for Docker not working with host DNS

Docker is a widely used application containerization platform that provides a portable, scalable, and scalable containerization environment. However, sometimes Docker will encounter various problems when used with host DNS, such as inability to resolve domain names, high latency, and so on. This article will introduce the reasons why Docker cannot be used with host DNS and the solutions.

Reason

Docker uses technologies such as Cgroups and Namespace to provide a completely isolated environment from the host in the container. This isolation environment protects the container, but also prevents the container from communicating through the host's DNS server. Therefore, the host DNS service cannot be used for domain name resolution inside the container.

Solution

In order to solve the problem that Docker cannot be used with the host DNS, we can take the following measures:

1. Set up a custom DNS server in the Docker container

We can set up a custom DNS server in Docker to replace the default DNS server. We can set up a custom DNS server by using the following command in the Dockerfile:

RUN echo "nameserver 8.8.8.8" >> /etc/resolv.conf

This will add Google’s public DNS server 8.8.8.8 to the /etc/resolv.conf file in the container. We can set up multiple DNS servers by adding multiple nameservers.

2. Set up Docker’s DNS server in the host machine

We can set up Docker’s DNS server in the host machine so that the container can perform domain name resolution through the host machine. We can set up the Docker DNS server by adding the following configuration in the /etc/docker/daemon.json file:

{
  "dns": ["8.8.8.8", "8.8.4.4"]
}

This will add Google’s public DNS servers 8.8.8.8 and 8.8.4.4 to the Docker DNS server middle. We can set up multiple DNS servers by adding multiple DNS servers.

3. Use the --dns option of the Docker container

We can use the --dns option when starting the Docker container to set the container's DNS server. For example:

docker run --dns 8.8.8.8 -it ubuntu:latest

This will set Google's public DNS server 8.8.8.8 as the container's DNS server.

Summary

Docker cannot be used with host DNS because Docker uses some technologies to provide an isolated environment in the container. To solve this problem, we can set a custom DNS server in the Docker container, set Docker's DNS server in the host, or use the --dns option of the Docker container to set the container's DNS server. These solutions allow Docker to work with host DNS so that we can better use the Docker containerization platform.

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