I did not find the reason why on my lab I was not able to edit the instance belonging to a running instance group to add the network tag.
As a workaround I delete the first group, edited the template with the network tag and created a second group based on the amended instance template, That worked and I could start the SSH session to one of the instances.
Can you guess what was wrong?
Hello, Marcel. Google has apparently been changing this behavior for some people (though not for me, when I tried it), because, as I mention in the video, it’s a shortcut and not best practice. (Though I also wanted to demonstrate how you can get things fixed back up, if they get out of sync.)
In any case, you should still (unless they’ve changed this, too) be able to get the tag applied using a simple
gcloud compute instances add-tags xyz123instance --tags=open-ssh-tag
(Plus the zone, if you haven’t set it.)