Assign way more replicas than you have of memory on all nodes and watch the Swarm crash which can easily reproduce in a small VMfor testing.
root@Deb11Docker01:~# docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAM........
A lot of times this is actually caused by simply not having Firefox installed at all.
selenium.common.exceptions.WebDriverException: Message: Can not connect to the Service geckodriver
https://github.com/mozilla/geckodriver/issues/270........