watchtower/docs/running-multiple-instances.md

By default, Watchtower will clean up other instances and won't allow multiple instances running on the same Docker host or swarm. It is possible to override this behavior by defining a scope to each running instance.

Notice that:

• Multiple instances can't run with the same scope;
• An instance without a scope will clean up other running instances, even if they have a defined scope;

To define an instance monitoring scope, use the --scope argument or the WATCHTOWER_SCOPE environment variable on startup and set the com.centurylinklabs.watchtower.scope label with the same value for the containers you want to include in this instance's scope (including the instance itself).

For example, in a Docker Compose config file:

version: '3'

services:
  app-monitored-by-watchtower:
    image: myapps/monitored-by-watchtower
    labels:
      - "com.centurylinklabs.watchtower.scope=myscope"

  watchtower:
    image: containrrr/watchtower
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock
    command: --interval 30 --scope myscope
    labels:
      - "com.centurylinklabs.watchtower.scope=myscope"