With command line patterns, you can specify patterns like "all,!ntpservers" but I can't figure out how to specify this in a playbook. I'm regularly running into cases where I have to install a client on all machines except the server.
You specify the hosts for a playbook on the line that begins with
From the documentation:
hostsline is a list of one or more groups or host patterns, separated by colons, as described in the Working with Patterns documentation.
--- - hosts: all,!ntpservers tasks: # ... your tasks here roles: # ... etc etc etc
These roles and tasks will be appled to
all hosts except