How to Resolve “Unknown MySQL Server Host ‘host.docker.internal'” Error

Hello Dev, if you’re reading this article, chances are you have encountered the “unknown MySQL server host ‘host.docker.internal'” error while attempting to connect to a MySQL server from your Docker container. This error can be frustrating, but don’t worry, we’re here to help. In this article, we’ll explain what causes this error and provide you with step-by-step instructions on how to resolve it.

What Causes the “Unknown MySQL Server Host ‘host.docker.internal'” Error?

The “unknown MySQL server host ‘host.docker.internal'” error occurs when you try to connect to a MySQL server from a Docker container using the hostname “host.docker.internal”. This hostname is used to refer to the host machine from inside the container. However, the error occurs because the container cannot resolve this hostname to the IP address of the host machine.

This error is specific to Docker containers running on macOS and Windows, as these operating systems use a virtual machine to run Docker. Linux users are not affected by this issue.

Step-by-Step Guide to Resolving the “Unknown MySQL Server Host ‘host.docker.internal'” Error

Step 1: Check Your Docker Version

The first step is to ensure that you are running a version of Docker that supports the “host.docker.internal” hostname. This hostname was introduced in Docker 17.12.0-ce, so if you’re running an older version of Docker, you’ll need to upgrade.

To check your Docker version, run the following command in your terminal:

Command	Description
docker -v	Displays the version of Docker that you’re running

If your version is older than 17.12.0-ce, you’ll need to upgrade to a newer version before continuing.

Step 2: Add “host.docker.internal” to Your Hosts File

The next step is to add an entry for “host.docker.internal” to your host machine’s hosts file. This will allow your container to resolve the hostname to the IP address of the host machine, which is necessary for connecting to a MySQL server running on the host machine.

To add an entry to your hosts file, follow these steps:

1. Open a terminal window
2. Enter the following command to open the hosts file in a text editor (replace “nano” with your preferred text editor):
   sudo nano /etc/hosts
3. Add the following line to the end of the file:
   127.0.0.1 host.docker.internal
4. Save and exit the text editor

Now your container will be able to resolve “host.docker.internal” to the IP address of the host machine.

Step 3: Restart Your Docker Container

The final step is to restart your Docker container. This will ensure that the changes you made to the hosts file are picked up by the container.

To restart your container, run the following command:

Command	Description
docker restart CONTAINER_NAME	Restarts the Docker container with the specified name

Replace “CONTAINER_NAME” with the name of your container. After the container has restarted, you should be able to connect to your MySQL server from inside the container using the hostname “host.docker.internal”.

FAQ

What is a Hosts File?

The hosts file is a text file on your operating system that maps hostnames to IP addresses. When you try to connect to a hostname, your operating system looks up the corresponding IP address in the hosts file. If an entry exists for the hostname, your operating system uses the IP address specified in the hosts file to connect to the server.

Can I Use a Different Hostname?

Yes, you can use a different hostname to connect to your MySQL server from inside a Docker container. However, you will need to ensure that the hostname is mapped to the IP address of the host machine in the container’s hosts file. The steps to do this will vary depending on the hostname that you choose.

Why Does This Error Only Occur on macOS and Windows?

This error occurs on macOS and Windows because these operating systems use a virtual machine to run Docker. This virtual machine runs a Linux kernel, which is used to host Docker containers. When you try to connect to a MySQL server from inside a container on macOS or Windows, the container’s hostname is resolved by the Linux kernel running in the virtual machine. However, the virtual machine cannot resolve the hostname “host.docker.internal” to the IP address of the host machine by default, which results in the error.

Are There Any Other Solutions to This Error?

Yes, there are other solutions to this error. One solution is to use the IP address of the host machine instead of the hostname “host.docker.internal” when connecting to the MySQL server from inside the container. Another solution is to use a Docker network instead of the default bridge network, which can sometimes resolve this error.

Conclusion

We hope that this article has helped you resolve the “unknown MySQL server host ‘host.docker.internal'” error. Remember, the key steps are to ensure that you are running a version of Docker that supports the hostname “host.docker.internal”, add an entry for “host.docker.internal” to your host machine’s hosts file, and restart your Docker container. If you have any further questions or comments, please feel free to leave them below.