From inside of a Docker container, how do I connect to the localhost of the machine?

From inside of a Docker container, how do I connect to the localhost of the machine hosting the container, and what configurations or network settings need to be adjusted to enable this connection?

To connect to the localhost of the machine hosting a Docker container from inside the container, you can follow these approaches:

Using host.docker.internal:

For users on Windows and Mac using Docker Desktop, host.docker.internal acts as an alias for localhost. This makes it easier to access services running on the host machine without needing to configure additional settings.

Using the --add-host Flag:

On Linux systems using Docker Engine, you can use the --add-host flag to add an entry to the container's /etc/hosts file. This allows you to define a hostname (e.g., host.docker.internal) that maps to the host machine's IP address.

Using the --network=host Flag:

Another option for Linux users is to use the --network=host flag when running the Docker container. This configuration enables the container to share the host's network stack, allowing direct access to localhost as if the container were running directly on the host machine.

Using the Host IP Address:

Alternatively, you can use the host machine's IP address to connect from within the Docker container. This involves identifying the IP address assigned to your host machine's network interface and using it to make connections.

Summary:

• Windows/Mac: Use host.docker.internal.
• Linux: Use the --add-host flag or the --network=host flag.
• General: Use the host machine's IP address if needed.

These methods provide flexibility based on the operating system and specific network configurations, enabling you to connect to the localhost of the host machine from within a Docker container.