Add SIDEKIQ_MEMORY_KILLER_SHUTDOWN_SIGNAL env var

It looks like SIGTERM may not be enough to shut down a Sidekiq process
when its RSS has gotten too big. This change will allow us to experiment
with sending SIGKILL instead of SIGTERM to Sidekiq processes on
gitlab.com.

CHANGELOG

@@ -44,6 +44,7 @@ v 7.11.0 (unreleased)
   - Allow to use non-ASCII letters and dashes in project and namespace name. (Jakub Jirutka)
   - Add footnotes support to Markdown (Guillaume Delbergue)
   - Add current_sign_in_at to UserFull REST api.
+  - Make Sidekiq MemoryKiller shutdown signal configurable
 
 v 7.10.2
   - Fix CI links on MR page

doc/operations/sidekiq_memory_killer.md

@@ -36,3 +36,5 @@ The MemoryKiller is controlled using environment variables.
   Existing jobs get 30 seconds to finish. After that, the MemoryKiller tells
   Sidekiq to shut down, and an external supervision mechanism (e.g. Runit) must
   restart Sidekiq.
+- `SIDEKIQ_MEMORY_KILLER_SHUTDOWN_SIGNAL`: defaults to 'SIGTERM'. The name of
+  the final signal sent to the Sidekiq process when we want it to shut down.

lib/gitlab/sidekiq_middleware/memory_killer.rb

@@ -7,6 +7,7 @@ module Gitlab
       GRACE_TIME = (ENV['SIDEKIQ_MEMORY_KILLER_GRACE_TIME'] || 15 * 60).to_s.to_i
       # Wait 30 seconds for running jobs to finish during graceful shutdown
       SHUTDOWN_WAIT = (ENV['SIDEKIQ_MEMORY_KILLER_SHUTDOWN_WAIT'] || 30).to_s.to_i
+      SHUTDOWN_SIGNAL = (ENV['SIDEKIQ_MEMORY_KILLER_SHUTDOWN_SIGNAL'] || 'SIGTERM').to_s
 
       # Create a mutex used to ensure there will be only one thread waiting to
       # shut Sidekiq down
@@ -24,19 +25,19 @@ module Gitlab
 
           Sidekiq.logger.warn "current RSS #{current_rss} exceeds maximum RSS "\
             "#{MAX_RSS}"
-          Sidekiq.logger.warn "spawned thread that will shut down PID "\
-            "#{Process.pid} in #{GRACE_TIME} seconds"
+          Sidekiq.logger.warn "this thread will shut down PID #{Process.pid} "\
+            "in #{GRACE_TIME} seconds"
           sleep(GRACE_TIME)
 
           Sidekiq.logger.warn "sending SIGUSR1 to PID #{Process.pid}"
           Process.kill('SIGUSR1', Process.pid)
 
           Sidekiq.logger.warn "waiting #{SHUTDOWN_WAIT} seconds before sending "\
-            "SIGTERM to PID #{Process.pid}"
+            "#{SHUTDOWN_SIGNAL} to PID #{Process.pid}"
           sleep(SHUTDOWN_WAIT)
 
-          Sidekiq.logger.warn "sending SIGTERM to PID #{Process.pid}"
-          Process.kill('SIGTERM', Process.pid)
+          Sidekiq.logger.warn "sending #{SHUTDOWN_SIGNAL} to PID #{Process.pid}"
+          Process.kill(SHUTDOWN_SIGNAL, Process.pid)
         end
       end