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.

I only use `nproc` and see it used in other containers as well, ie `bundle install -j $(nproc)`. This honors cpu assignment and provides the functionality you're seeking. Whether or not random application software uses nproc if available, idk

> Print the number of processing units available to the current process, which may be less than the number of online processors. If this information is not accessible, then print the number of processors installed

https://www.gnu.org/software/coreutils/manual/html_node/npro...

https://www.flamingspork.com/blog/2020/11/25/why-you-should-...

This is not very robust. You probably should use the cgroup cpu limits where present, since `docker --cpus` uses a different way to set quota:

    if [[ -e /sys/fs/cgroup/cpu/cpu.cfs_quota_us ]] && [[ -e /sys/fs/cgroup/cpu/cpu.cfs_period_us ]]; then
        GOMAXPROCS=$(perl -e 'use POSIX; printf "%d\n", ceil($ARGV[0] / $ARGV[1])' "$(cat /sys/fs/cgroup/cpu/cpu.cfs_quota_us)" "$(cat /sys/fs/cgroup/cpu/cpu.cfs_period_us)")
    else
        GOMAXPROCS=$(nproc)
    fi
    export GOMAXPROCS

This follows from how `docker --cpus` works (https://docs.docker.com/config/containers/resource_constrain...), as well as https://stackoverflow.com/a/65554131/207384 to get the /sys paths to read from.

Or use https://github.com/uber-go/automaxprocs, which is very comprehensive, but is a bunch of code for what should be a simple task.