One of the common problems with Ruby is its memory usage, just like JVM-based languages (yes Java, I'm talking about you). Actually, Ruby just like Java is based on garbage collector. This GC, if not used correctly, can cause "stop the world scenarios" (as we can see in the attached diagram). In these cases, the GC actually stops responding while consuming the server's whole CPU and in some cases even causes a server reboot.
Unicorn and Ruby memory leak causes server downtime.
What Can Be Done?
Reboot Your Ruby Periodically
Installing the killer:
Add to config.ru above "require ::File.expand_path('../config/environment', __FILE__)"
# Unicorn self-process killer require 'unicorn/worker_killer'
And decide your worker graceful reboot method:
# Max requests per worker use Unicorn::WorkerKiller::MaxRequests, 3072, 4096 # Max memory size (RSS) per worker use Unicorn::WorkerKiller::Oom, (192*(1024**2)), (256*(1024**2))
If you are using Ruby 2.X, you can exploit the CoW by better configuring Unicorn.
- - worker_processes: 1x your cores
- - timeout: worker request timeout, should be 15 to 30 sec max
- - preload_app: enables CoW, but requires managing connect/disconnect on fork
Take Care of GC Configuration
The Bottom Line
Dynamic languages have their downs, yet w/ the right design you can keep them up and running.
Keep Performing! -Moshe Kaplan