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Docker is an open source application container engine that enables developers to build, deploy and run applications. Containerized applications are often made up of multiple components that need to communicate with each other to complete tasks. However, when using Docker, sometimes you encounter the problem that the domain name cannot be resolved, which results in the inability to communicate between containers or the inability to connect to external services. In this article, we'll cover some common causes and solutions to help you resolve this issue quickly.
In Docker containers, domain name resolution is usually completed through the DNS server. When Docker cannot resolve a domain name, it may be due to a DNS server failure or network instability. In order to solve this problem, you can do the following:
1.1 Check the DNS server configuration
First, you can check whether the DNS configuration of Docker is correct. You can run the following command in the container:
cat /etc/resolv.conf
to check whether the DNS server is configured correctly.
If the DNS server is misconfigured, you can specify the correct DNS server address by appending the --dns
option when the Docker daemon is started. For example:
dockerd --dns 8.8.8.8
2.2 Modify the container DNS configuration
Docker also provides a method to set the container DNS configuration. You can specify the DNS server address when creating the container using the --dns
option. For example:
docker run --dns 8.8.8.8 nginx
In addition, you can also configure the DNS server address in the /etc/docker/daemon.json
file. For example:
{ "dns": ["8.8.8.8", "8.8.4.4"] }
After restarting the Docker daemon, these configurations will take effect.
Docker containers run on the host. If the host network connection is unstable, the Docker container may not be able to access external services or communicate with other containers. communication. The following are several possible solutions:
2.1 Check the host network connection
You can run the ping
command on the host to test the network connection. For example:
ping www.baidu.com
If you cannot connect, you can try to restart the host or contact the network administrator to solve the problem.
2.2 Check the Docker bridge configuration
Docker has a default network mode called bridge (bridge), and the container communicates with the host and other containers through this bridge. If the bridge configuration is incorrect, the container may not be able to resolve the domain name, so you can view the Docker bridge configuration on the host machine and make adjustments. You can check it with the following command:
docker network inspect bridge
If there is a problem, you can use the following command to re-create the bridge:
docker network create bridge
In In some cases, problems with domain name resolution caching may occur when communicating between containers and external services. This may cause the domain name to fail to be resolved or the DNS resolution results to be delayed. If such a problem occurs, you can perform the following operations:
3.1 Clear the DNS cache
You can execute the following command in the container to clear the DNS cache:
/etc/init.d/nscd restart
If in the host If you encounter this problem on the host, you can try the following command:
sudo service dns-clean restart
3.2 Modify the DNS cache threshold
If there is a delay in the DNS resolution results, you can try to modify the DNS cache threshold. You can run the following command in the container:
echo 2000 > /proc/sys/net/ipv4/neigh/default/gc_stale_time
This will set the DNS cache threshold to 2000 milliseconds.
Summary
When using Docker, it is very common to encounter the problem of being unable to resolve domain names. This problem may be caused by various factors such as DNS server configuration, network connection, or DNS resolution cache. There are many ways to solve this problem, which can be solved by checking the DNS server configuration, modifying the container DNS configuration, checking the host network connection, checking the Docker bridge configuration, clearing the DNS cache, or modifying the DNS cache threshold. I hope the solutions provided in this article can help you solve the problem quickly and make better use of the Docker container engine.
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