The Short Answer

To fix the “Restart Policy” issue in Docker and achieve an “unless-stopped” state, advanced users can directly modify the container’s restart policy using the Docker CLI command docker update --restart=unless-stopped <container_name>. This command ensures that the container will only restart unless it is explicitly stopped.

Why This Error Happens

• Reason 1: The most common cause of this issue is that the default restart policy in Docker is set to “no” or another policy that does not meet the “unless-stopped” requirement. When a container is created without specifying a restart policy, it defaults to “no”, which means the container will not restart automatically after a failure or system reboot.
• Reason 2: An edge case cause is when the Docker daemon configuration overrides the container’s restart policy. For example, if the Docker daemon is configured with a global restart policy, it can override the policy set for individual containers.
• Impact: Container downtime and potential data loss can occur if the container is not configured to restart automatically when needed, leading to service disruptions and impacting overall system reliability.

Step-by-Step Solutions

Method 1: The Quick Fix

1. Go to Docker Desktop > Settings > Docker Engine (for Docker Desktop users) or edit the /etc/docker/daemon.json file (for Linux users).
2. Toggle the “Restart policy” option to “unless-stopped” for the specific container or set the global default to “unless-stopped”.
3. Refresh the Docker service or restart the Docker daemon for the changes to take effect.

Method 2: The Command Line/Advanced Fix

To set the restart policy to “unless-stopped” for a container using the Docker CLI, run the following command:

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docker update --restart=unless-stopped <container_name>

Replace <container_name> with the name of your container. This command directly updates the restart policy of the specified container.

Prevention: How to Stop This Coming Back

• Best practice configuration: Always specify the restart policy when creating containers, especially in production environments, to ensure they behave as expected after failures or system reboots.
• Monitoring tips: Regularly monitor container statuses and Docker daemon logs to quickly identify and address any issues related to restart policies.

If You Can’t Fix It…

[!WARNING] If Docker keeps crashing or you are unable to resolve the restart policy issue, consider switching to Podman, which handles container restart policies natively and may offer more robust and reliable container management without these errors.

FAQ

Q: Will I lose data fixing this? A: Modifying the restart policy of a container does not directly affect the data stored within the container. However, if the container is restarted due to a policy change, any unsaved data in memory may be lost. It’s essential to ensure that applications within containers are designed to handle restarts gracefully.

Q: Is this a bug in Docker? A: The need to manually configure the restart policy is not a bug in Docker but rather a feature that allows for flexibility in container management. Docker’s default behavior is designed to be secure and prevent unintended container restarts. The “unless-stopped” policy is a specific configuration that needs to be set based on the requirements of the application or service being containerized. As of Docker version 20.10 and later, the restart policy configuration has been streamlined, making it easier to manage container restart behaviors.

📚 Continue Learning

Check out our guides on Docker and Restart Policy.