I’m testing out custom parallelism in my branch, but in the meantime would prefer for builds on the rest of the repo not take up extra containers they’re not using (I’ve checked; there’s no automatic gain from adding containers because of how our test runner works). Is there a way to automatically set number of containers at build time (i.e. in circle.yml) or at least only for a single branch?
(Also, the “paralellism” tag here on the Discuss site is misspelled–should be “parallelism” 
.)
We would also find this very useful. When we buy extra containers, we would like to bump the parallelism for all our users.
Without a way to change parallelism automatically, some users forget to update their settings, and we find ourselves not getting the expected value out of our containers.
It would be great to have this feature. Our entire app is split into micro services and each of these are further split into modules. For example, a user module (dealing with authorization) is same throughout these microservices. Most often nothing gets added to this module and we have a setup which checks for changes in such modules and run only specs from these modules.
Now, we run all these specs on master/production/staging branches, and such full builds take up time.
Say I have an option to run a script which checks on which branch this build currently in, if in master, run with 16x parallelism, if not then run with 4x parallelism.