Safely Migrate and Backup Docker Containers with Snap and Official Installations

Migrating and Backing Up Docker Containers: Solving a Major Live Migration Issue

When managing Docker containers in production environments, it’s common to encounter situations where you need to migrate Docker from Snap to the official Docker installation. This process can be quite tricky, especially if you’re dealing with live running containers. In this guide, we’ll walk you through how to successfully migrate your Docker installation, backup data, and restore your containers while minimizing downtime.

In some cases, issues can arise with Docker Snap installations, leading to performance or compatibility issues. Here, we cover everything you need to know to resolve these problems while ensuring your services remain as stable as possible.

Step-by-Step Guide to Migrating Docker Containers from Snap to Official Installation

Step 1: Preparation & Inventory

Before starting, ensure you have a clear understanding of your running containers and their associated volumes.

List Running Containers and Check Volumes
- Command to list containers:
  docker ps
- Identify Docker volumes:
  docker volume ls
Example output might include:
- influxdb_influxdb-config (volume name)
- influxdb_influxdb-data (volume name)
Identify Data Locations
There are two potential Docker data locations:
- Snap Docker Data Directory: /var/snap/docker/
- Official Docker Data Directory: /var/lib/docker/
Estimate the size of your data:
sudo du -sh /var/snap/docker/common/var-lib-docker/
You’ll see an output like:
20G /var/snap/docker/common/var-lib-docker/

Step 2: Backup Your Docker Containers, Images, and Volumes

Before making any changes, ensure you back up your data:

Stop the Running Containers Gracefully
- Stop the container:
  docker stop my_container
- For Snap Docker:
  sudo snap stop docker
- For system-wide Docker service:
  sudo systemctl stop docker
Backup Snap Docker Data to Official Docker Folder
Create a backup of Snap Docker data:
sudo tar -cvzf /home/user/docker_backup.tar.gz /var/snap/docker/common/var-lib-docker
This will take around 25-35 minutes depending on the size.

Step 3: Remove Snap Docker & Restore Backups

Now that your backup is complete, you can proceed with the removal of the Snap Docker installation and restore the data to the official Docker directory.

Disable Snap Docker
Disable the Snap version of Docker:
sudo snap disable docker
Remove Snap Docker
Remove Docker via Snap:
sudo snap remove docker
Snap automatically creates a snapshot, which is useful for recovery. If something goes wrong, you can restore it using:
sudo snap restore <snapshot-id>
Restore Your Docker Data
Extract the backup and move the data to the official Docker directory:
sudo tar -xvzf /home/user/docker_backup.tar.gz -C /var/lib/docker/
Alternatively, you can copy the backup files to the official Docker directory:
sudo mv /var/lib/docker /var/lib/docker_backup_old sudo cp -a /home/user/old-snap-docker-backup/var/snap/docker/common/var-lib-docker/. /var/lib/docker/
You can also choose to make a volume-specific backup:
sudo tar -cvzf /root/docker-backups/your_volume_name.tar.gz /path/to/your/volume

Step 4: Restart Docker Service

Once the data is restored, it’s time to reload the systemd configuration and restart the Docker service.

Reload the Systemd Configuration
sudo systemctl daemon-reload
Restart Docker
sudo systemctl restart docker

Step 5: Start Docker Containers

Finally, start your Docker container again:

You can check the logs of the container to ensure everything is running smoothly:

Troubleshooting Common Issues

During the migration process, you might encounter issues such as permission errors or data inconsistencies. Here’s how to troubleshoot common problems:

Permission Issues: If you face permission issues when restoring Docker data, run:
sudo aa-remove-unknown
Service Not Starting: If Docker isn’t starting correctly, check the system logs for any specific error messages:
sudo journalctl -u docker
Inconsistent Data After Restoration: If you notice that the restored data isn’t identical to the original, ensure that you’ve correctly backed up all relevant data before removal. The system might also require additional configuration to properly restore all settings.

Case Study: Resolving a Live Running Docker Container Migration

Let’s dive into a real-world case where this process was applied to a live running Docker container. In our case, a Docker installation on Snap was causing performance degradation due to limitations in container management. The solution was to migrate the Docker setup to the official installation while ensuring minimal downtime.

By following the steps outlined in this guide, we were able to safely back up the running container and volumes, remove Snap Docker, and restore everything to the official Docker directory. The downtime for this process was estimated at approximately 20-30 minutes, as most of the time was spent on data transfer and ensuring everything was properly restored.

Conclusion: Successful Migration with Minimal Downtime

Migrating Docker containers from Snap to the official installation can be a challenging task, but it’s a necessary step when dealing with performance issues or compatibility problems. By carefully following the backup, restore, and migration steps, you can ensure minimal downtime and prevent data loss. Always keep your backups up to date and test the process in a staging environment to avoid surprises.

By taking preventive steps and understanding the underlying issues, you can ensure a smooth migration and continued stability of your Docker containers.