docker-volume-backup/docs/how-tos/use-with-docker-swarm.md

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Use with Docker Swarm	default	How Tos	13

Use with Docker Swarm

{: .note } The mechanisms described in this page do only apply when Docker is running in Swarm mode.

Stopping containers during backup

Stopping and restarting containers during backup creation when running Docker in Swarm mode is supported in two ways.

Scaling services down to zero before scaling back up

When labeling a service in the deploy section, the following strategy for stopping and restarting will be used:

• The service is scaled down to zero replicas
• The backup is created
• The service is scaled back up to the previous number of replicas

{: .note } This approach will only work for services that are deployed in replicated mode.

Such a service definition could look like:

services:
  app:
    image: myorg/myimage:latest
    deploy:
      labels:
        - docker-volume-backup.stop-during-backup=true
      replicas: 2

Stopping the containers

This approach bypasses the services and stops containers directly, creates the backup and restarts the containers again. As Docker Swarm would usually try to instantly restart containers that are manually stopped, this approach only works when using the on-failure restart policy. A restart policy of always is not compatible with this approach.

Such a service definition could look like:

services:
  app:
    image: myapp/myimage:latest
    labels:
      - docker-volume-backup.stop-during-backup=true
    deploy:
      replicas: 2
      restart_policy:
        condition: on-failure

---

Memory limit considerations

When running in Swarm mode, it's also advised to set a hard memory limit on your service (~25MB should be enough in most cases, but if you backup large files above half a gigabyte or similar, you might have to raise this in case the backup exits with Killed):

services:
  backup:
    image: offen/docker-volume-backup:v2
    deployment:
      resources:
        limits:
          memory: 25M