I still use the fool out of vagrant. I often have to write small tools that run across 10000s of servers running various versions of OSes (but all x86 these day

I still use the fool out of vagrant. I often have to write small tools that run across 10000s of servers running various versions of OSes (but all x86 these days, thankfully). Almost always I need to hit /proc, /sys, and various glibc versions, so having a full kernel and user space is better than fussing with Docker. It lets me test against all of them pretty easily. Tear down, spin up, repeat. I learned that various versions of RHEL6 kernels have stuff like epoll() but others don’t and it’s not everything after kernel version X.Y. Joy. Better than before when I had to support HP-UX, Solaris, AIX, etc. At least I have a consistent shell and least common denominator tools. That was like old school browser detection. But yeah, a lot of focus on doing work without stressing the machine at all to not impact business workloads. Not my “day job”, but get pulled into emergencies because folks trust that I’ll do it. Log4j2 detection/validation was not fun. That was a “real cli” with a degraded pure shell fallback. And due to the lack of predictably, that was a try, fail, degrade. Nested jars/wars/ears suck when you can’t just play in memory. I run macOS with virtualbox locally, but can get all the Linuxes I need and quickly ruby/shell a test harness. Only annoying thing is remembering to remove them all when I’m done to get that disk back.