I got bit by env vars a few years back, but due to performance issues in getenv() and ended up writing a whole bunch of PHP magic to ship config files safely an

I got bit by env vars a few years back, but due to performance issues in getenv() and ended up writing a whole bunch of PHP magic to ship config files safely and fast. With pecl/hidef, I can hook a bunch of text .ini files into the PHP engine and defines constants as each requests comes in. Originally, it was written for a nearly static website, which was spending a ridiculous amount of time defining constants, which rolled over every 30 minutes. Plus those .ini files were only readable to root, which reads it and then forks off the unprivileged processes. But with the hidef.per_request_ini, I could hook that into the Apache2 vhost settings, so that the exact same code would operate with different constants across vhosts without changing any code between them. Used two different RPMs to push those two bits so that I could push code & critical config changes as a two-step process. And with a bit of yum trickery (the yum-multiverse plugin), I could install two versions of code and one version of config, and other madness like that with the help of update-alternatives. That served as an awesome A/B testing setup, to innoculate a new release with a fraction of users hitting a different vhost for the micro-service. I'm rambling now, but the whole point is that you need per-request/per-user config overlay layers, for which env vars are horrible, slow and possibly printed everytime someone throws some diagnostics up.