How can we back up the metadata for Docker Swarm?

Backing up the metadata for Docker Swarm is crucial for ensuring the resilience and recovery of Swarm modes. The most reliable method is to back up the data located at /var/lib/docker/swarm while the Docker daemon is stopped. This directory contains important files that include the state of the Swarm, secrets, and service definitions. When the Docker daemon is running, any changes or operations may result in incomplete or inconsistent backups, which can lead to restore issues. By stopping the Docker daemon before performing the backup, you can ensure that the data is stable and that you are capturing the full Swarm state accurately.

Other methods may not provide the same level of reliability. Copying the Docker configuration files may not include all of the necessary Swarm metadata, while accessing /var/lib/docker/swarm while the daemon is running risks capturing an unstable state. Using third-party backup tools could be useful but may not specifically address the nuances of Docker Swarm metadata backup, making it less reliable than the method involving the stopping of the Docker daemon.