How do you configure automatic container restarts in Docker?

In Docker, the primary method for configuring automatic container restart is by utilizing restart policies. Docker provides several distinct restart policies that you can select based on your requirements. These policies include:

1. no: This is the default setting, where the container does not restart automatically upon exit.
2. always: Regardless of the container's exit status, the container will always restart.
3. unless-stopped: The container will always restart unless explicitly stopped by the user, even during the Docker daemon's startup or restart.
4. on-failure: The container restarts only when it exits abnormally (exit status is non-zero). You can optionally specify the maximum number of restart attempts.

For instance, if you want your container to automatically attempt restarts when it encounters errors, use the --restart on-failure option when running the container. You can also add an optional limit on the number of restart attempts, such as:

bash
docker run --restart=on-failure:5 your-image

This command instructs Docker to attempt restarting the container up to five times, exclusively when the container's exit code is non-zero.

If you require the container to restart regardless of the exit status, employ the always policy:

bash
docker run --restart=always your-image

This ensures the container always attempts to restart after stopping, which is particularly valuable in production environments to maintain continuous operation of critical services.

Consider a practical scenario: suppose you have a web server container and want it to automatically restart after crashing to continue providing service. Use the following command:

bash
docker run --restart=always -d -p 80:80 your-webserver-image

This command sets the always restart policy, guaranteeing the web server restarts automatically in any exit scenario. The -d parameter runs the container in the background, and -p 80:80 maps port 80 inside the container to port 80 on the host for external access.

By implementing this configuration, you can enhance the stability and reliability of container operations.