puma: add puma worker killer gem.

Gemfile

@@ -54,6 +54,7 @@ gem 'terminal-table'
 gem 'newrelic_rpm', require: false
 gem 'clockwork'
 gem 'puma-metrics'
+gem 'puma_worker_killer'
 
 group :production, :staging do
   gem 'unicorn', :platforms => :ruby

Gemfile.lock

@@ -331,6 +331,9 @@ GEM
     puma-metrics (1.2.3)
       prometheus-client (>= 0.10)
       puma (>= 3.0)
+    puma_worker_killer (0.3.1)
+      get_process_mem (~> 0.2)
+      puma (>= 2.7)
     pundit (2.1.1)
       activesupport (>= 3.0.0)
     racc (1.5.2)
@@ -562,6 +565,7 @@ DEPENDENCIES
   pry-rails
   puma
   puma-metrics
+  puma_worker_killer
   pundit
   rack-mini-profiler
   rails (~> 6.0)

config/puma.rb

@@ -13,6 +13,7 @@
 # * PUMA_PIDFILE
 # * PUMA_CONTROL_URL
 # * PUMA_METRICS_URL
+# * PUMA_RESTART_INTERVAL
 #
 # Use `bin/pumactl` to control a running Puma instance.
 #
@@ -105,3 +106,12 @@ metrics_url ENV.fetch("PUMA_METRICS_URL", "tcp://localhost:9393")
 #
 # https://github.com/puma/puma#controlstatus-server
 activate_control_app ENV.fetch("PUMA_CONTROL_URL", "tcp://localhost:9293"), no_token: true
+
+# https://github.com/schneems/puma_worker_killer
+# https://docs.gitlab.com/ee/administration/operations/puma.html#puma-worker-killer
+before_fork do
+  require 'puma_worker_killer'
+
+  PumaWorkerKiller.rolling_restart_splay_seconds = 0.0..180.0 # 0 to 3 minutes in seconds
+  PumaWorkerKiller.enable_rolling_restart ENV.fetch("PUMA_RESTART_INTERVAL", 2 * 60 * 60).to_i # every 2 hours by default
+end