The common problem I see across many languages is: applications detect machine cores by looking at /proc/cpuinfo. However, in a docker container (or other container technology), that file looks the same as the container host (listing all cores, regardless of how few have been assigned to the container).

I wondered for a while if docker could make a fake /proc/cpuinfo that apps could parse that just listed "docker cpus" allocated to the job, but upon further reflection, that probably wouldn't work for many reasons.