Share some reasons and solutions for why Docker containers cannot access the Internet

With the widespread use of Docker in recent years, sometimes we encounter some problems when using Docker, such as the problem we are going to discuss today: the docker container cannot access the Internet. This problem is very common when using Docker, but it is also a very annoying and headache-inducing problem. Today we will share some reasons why Docker containers cannot access the Internet and their solutions.

1. Check the network settings of the container

First, we need to check the network settings of the container to ensure that the network settings are correct. When we use Docker to create a container, we can set the network type and network configuration of the container. If the network type is configured as "none", the container will not be able to access the Internet. And if the network type is configured as "bridge", the container can access the Internet through the host's network.

We can use the following command to view the network settings of the container:

docker inspect <容器名或 ID> | grep NetworkMode

If the output result is "none", then we need to use the following command to set the container network type to "bridge":

docker run --net=bridge <镜像名>

In this way, the container can access the Internet through the host network.

2. Check the DNS configuration of the container

The reason why another container cannot access the Internet is that the DNS configuration is incorrect. When we execute commands inside the container or on the host, we need to use DNS to resolve the domain name. If the DNS configuration is incorrect, the container will not be able to resolve the domain name and will not be able to access the Internet.

We can use the following command to check the DNS configuration of the container:

docker inspect <容器名或 ID> | grep -i dns

If the output result is empty, then we need to set the DNS configuration manually. We can manually set the DNS configuration when creating the container using the following command:

docker run --dns=<DNS 服务器> <镜像名>

In the above command, we can configure the DNS server to our own DNS server address, such as 8.8.8.8.

3. Check the firewall settings of the container

Sometimes the reason why the container cannot access the Internet is also related to the firewall settings of the container. The firewall in the container is enabled by default and blocks all inbound and outbound traffic.

We can use the following command to check the firewall settings of the container:

docker exec <容器名或 ID> iptables -L

If the firewall is enabled, we can use the following command to turn off the firewall:

docker exec <容器名或 ID> iptables -P INPUT ACCEPT
docker exec <容器名或 ID> iptables -P FORWARD ACCEPT
docker exec <容器名或 ID> iptables -P OUTPUT ACCEPT
docker exec <容器名或 ID> iptables -F

The meaning of the above command is Set the default policy of the container's firewall to Accept, and then clear all firewall rules.

4. Check the firewall settings of the host computer

If the above three solutions do not solve the problem, then we should check the firewall settings of the host computer. If the host's firewall is not configured correctly, it may block the container's traffic, causing the container to be unable to access the Internet.

We can use the following command to check the firewall settings of the host:

iptables -L

If the firewall is enabled, we can use the following command to open the firewall of the host:

iptables -P INPUT ACCEPT
iptables -P FORWARD ACCEPT
iptables -P OUTPUT ACCEPT
iptables -F

Above The meaning of the command is to set the default policy of the host's firewall to accept, and then clear all firewall rules.

Summary

In short, when we encounter the problem that the Docker container cannot access the Internet, we first need to check the network settings, DNS configuration and firewall settings of the container. If these are ok, we should check the host's firewall settings. I hope today's article will be helpful to everyone who encounters problems when using Docker.

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