Running Docker on AlmaLinux: Troubleshooting Firewall Issues with CFFirewall (firewall script)

Running Docker on Alma Linux: Troubleshooting Firewall Issues with firewalld (FirewallD)

You have recently upgraded your Docker software and have been asked to install and run it on an Alma Linux system. However, you have encountered an issue where the firewall is blocking Docker from functioning correctly. This article will guide you through troubleshooting and resolving this problem using firewalld, the firewall management tool in Alma Linux.

Understanding Firewalld

Firewalld is a dynamic firewall management tool that is present in most modern Linux distributions, including Alma Linux. It provides a way to manage firewall rules and configurations using a simple and consistent interface, both through the command line and through a graphical user interface. Firewalld uses firewall "zones" to define policies for incoming and outgoing network traffic.

Checking the Current Firewall Configuration

Before taking any action, it's important to check the current firewall configuration. You can do this by running the following command:

sudo firewall-cmd --list-all-zones

This will display a list of all the configured zones, along with the currently active rules for each zone. Take note of the active zone, as this is the zone that will be relevant for the rest of this troubleshooting process.

Adding Docker to the Firewall Configuration

To allow Docker to function properly, you need to add it to the firewall configuration. You can do this by running the following command:

sudo firewall-cmd --permanent --add-service=docker

This will add the "docker" service to the permanent firewall configuration. The "--permanent" option ensures that the change will persist even after a firewall reload or restart. To apply the changes immediately, you can run

sudo firewall-cmd --reload

Checking Docker Connectivity

After adding the Docker service to the firewall configuration, you can check if Docker is now able to connect to the network. You can do this by running the following command:

sudo docker run --rm hello-world

If Docker is able to connect to the network, you should see the "Hello from Docker!" message. If not, you may need to further troubleshoot the issue.

Further Troubleshooting

If you are still experiencing problems, there are a few additional steps you can take:

• Check that the firewall is actually running by running the command

  sudo systemctl status firewalld

• Check that the Docker service is running by running the command

  sudo systemctl status docker

• Check that the Docker daemon is listening on the correct network ports by running the command

  sudo netstat -tulnp | grep docker

• Check that the network settings of the system are correctly configured for Docker.

In this article, we have covered the basics of Firewalld, how to add Docker to the firewall configuration, and how to check Docker connectivity. By following these steps, you should be able to resolve issues related to the firewall blocking Docker on an Alma Linux system. If you continue to experience problems, it is recommended to consult further resources, such as the Alma Linux documentation or Docker documentation, for additional troubleshooting guidance.

References

• Alma Linux Firewalld documentation
• Docker Firewall documentation