Sorry but I can’t provide any help for self created containers and stuff.
However, as you seem still to be using a vanilla version of Zammad, the following page may help you:
https://docs.zammad.org/en/latest/appendix/configure-env-vars.html#performance-tuning
What you want is that your puma does not permanently stick at 100%. It’s perfectly normal if it does from time to time, that is bound to shipping information to your user.
WEB_CONCURRENCY and ZAMMAD_SESSION_JOBS_CONCURRENT should be able to solve your issues if you have enough cpu power which I currently expect.
The first option is for the number of web processes Zammad spawns. If you have 50 or more concurrent users, you’ll typically may need somewhat between 4 and 12 processes. The second environment variable allows you to spawn more than one session worker. This is required if Zammad no longer can keep up with updating your overviews for example.
Above is just a very rough idea.
It’s nearly impossible to provide a good working set for every system, as every system behaves differently. (not just in power terms)
And yes, it’s correct that Zammad doesn’t allow several railsservers to run. With above options this shouldn’t be required in terms of performance fiddling.