Docker Restart Policy

always Restart Policy

• Behavior: The container is always restarted, regardless of the exit status. It doesn’t matter if the container exited with an error or normally, Docker will restart it.
• Use Case: This policy is useful for services that need to be running continuously and should not be stopped for any reason. For example, web servers, databases, or any critical background services.
• Example: If you stop a container manually with docker stop or docker kill, it will still be restarted automatically.

on-failure Restart Policy

• Behavior: The container is restarted only if it exits with a non-zero exit code (indicating an error). If the container exits successfully (with an exit code of 0), it will not be restarted.
• Use Case: This policy is useful for applications that should only restart if they fail due to an error but can be allowed to stop if they complete their task successfully. For example, batch jobs, data processing tasks, or short-lived services.
• Example: If you stop the container manually with docker stop or docker kill, it will not be restarted. Similarly, if the container exits successfully, it won’t be restarted either.

Example of Usage

You can set these restart policies using the --restart flag with the docker run command:

# `always` restart policy
docker run --restart always my-container

# `on-failure` restart policy
docker run --restart on-failure my-container