Puma Worker Configuration (#1701)

We noticed that the current default settings perform very poorly under
load. We managed to literally take down Greenlight during a larger event
when people where accessing the landing page for rooms and when doing
some tests, I was more or less able to DoS Greenlight on my own.

This patch adds a default worker configuration similar to the previous
configuration with one worker, but lets users easily adjust it to more
workers which significantly improves the situation. The small, 4 core
machine I was testing on could handle about thrice the amount of
requests.

Co-authored-by: Ahmad Farhat <ahmad.af.farhat@gmail.com>

config/puma.rb

@@ -23,14 +23,14 @@
 # Workers do not work on JRuby or Windows (both of which do not support
 # processes).
 #
-# workers ENV.fetch("WEB_CONCURRENCY") { 2 }
+workers ENV.fetch("WEB_CONCURRENCY") { 1 }
 
 # Use the `preload_app!` method when specifying a `workers` number.
 # This directive tells Puma to first boot the application and load code
 # before forking the application. This takes advantage of Copy On Write
 # process behavior so workers use less memory.
 #
-# preload_app!
+preload_app!
 
 # Allow puma to be restarted by `rails restart` command.
 plugin :tmp_restart

sample.env

@@ -268,7 +268,7 @@ CABLE_ADAPTER=postgresql
 DEFAULT_REGISTRATION=open
 
 # Preupload Presentation Storage
-# 
+#
 # By default, if Preupload Presentation is enabled for rooms, presentations are uploaded locally to ~/greenlight/storage
 # If you prefer to use AWS S3 or GCS Storage, you can set the variables below
 #
@@ -287,3 +287,15 @@ DEFAULT_REGISTRATION=open
 # GCS_CLIENT_CERT=
 # GCS_PROJECT=
 # GCS_BUCKET=
+
+# Web server settings
+#
+# The size of the thread pool per worker used by Greenlight's web server.
+# For details, see: https://github.com/puma/puma#thread-pool
+# Default: 5
+#RAILS_MAX_THREADS=5
+
+# The amount of workers (separate processes) used by the web server.
+# For details, see: https://github.com/puma/puma#clustered-mode
+# Default: 1
+#WEB_CONCURRENCY=1