Support for Redis Sentinel

app/controllers/health_checks_controller.rb

@@ -45,7 +45,11 @@ def check_database
   end
 
   def check_redis
-    Redis.new.ping
+    if Greenlight::Application.config.cache_store == :null_store
+      Redis.new.ping
+    else
+      Redis.new(Greenlight::Application.config.cache_store[1].except(:adapter, :channel_prefix)).ping
+    end
   rescue StandardError => e
     raise "Unable to connect to Redis - #{e}"
   end

bin/start

@@ -17,11 +17,13 @@ if [ "$RAILS_ENV" = "production" ]; then
     sleep 1
   done
 
-  while ! nc -zw3 $RDHOST $RDPORT
-  do
-    echo "Waiting for redis to start up ..."
-    sleep 1
-  done
+  if [ -z "$REDIS_SENTINEL" ]; then
+    while ! nc -zw3 $RDHOST $RDPORT
+    do
+      echo "Waiting for redis to start up ..."
+      sleep 1
+    done
+  fi
 fi
 
 rails assets:precompile

config/cable.yml

@@ -22,5 +22,9 @@ test:
 
 production:
   adapter: redis
-  url: <%= ENV.fetch("REDIS_URL", "") %>
+  url: <%= ENV.fetch("REDIS_URL", nil) || "redis://mymaster" %>
+  sentinels: <%= ENV.fetch("REDIS_SENTINEL", "") %>
+  name: mymaster
+  role: master
+  namespace: greenlight3
   channel_prefix: greenlight_production

config/environments/production.rb

@@ -18,6 +18,43 @@
 
 require 'active_support/core_ext/integer/time'
 
+class String
+  def string_between_markers(marker1, marker2)
+    self[/#{Regexp.escape(marker1)}(.*?)#{Regexp.escape(marker2)}/m, 1]
+  end
+end
+
+def parse_sentinels(sentinel_str)
+  work_str = sentinel_str.gsub(/[[:space:]]/, '').delete_prefix('[').delete_suffix(']') # remove all white space and surrounding []
+  sentinel_arr = []
+  until work_str.empty?
+    # cut string with hash content
+    sub_str = work_str.string_between_markers('{', '}')
+    # convert that string to hash (while converting keys to symbols and
+    # values to integer, if possible, else make it string without single quotes)
+    sub_arr = sub_str.split(',').map do |h|
+      h1, h2 = h.split(':')
+      { h1.to_sym => h2.match?(/\D/) ? h2.delete("'") : h2.to_i }
+    end
+    sub_hash = sub_arr.reduce(:merge)
+    sentinel_arr.append(sub_hash)
+    # remove hash string from current working string and delete any surrounding commas
+    work_str.slice! "{#{sub_str}}"
+    work_str = work_str.delete_prefix(',').delete_suffix(',')
+  end
+  sentinel_arr
+end
+
+def config_cache_store
+  if ENV.fetch('REDIS_SENTINEL', nil).present?
+    [:redis_cache_store, { sentinels: parse_sentinels(ENV.fetch('REDIS_SENTINEL')),
+                           url: ENV.fetch('REDIS_URL', nil) || 'redis://mymaster',
+                           name: 'mymaster', role: :master }]
+  else
+    [:redis_cache_store, { url: ENV.fetch('REDIS_URL', nil) }]
+  end
+end
+
 Rails.application.configure do
   # Settings specified here will take precedence over those in config/application.rb.
 
@@ -111,7 +148,7 @@
   config.log_tags = [:request_id]
 
   # Use a different cache store in production.
-  config.cache_store = :redis_cache_store, { url: ENV.fetch('REDIS_URL', nil) }
+  config.cache_store = config_cache_store
 
   # Use a real queuing backend for Active Job (and separate queues per environment).
   config.active_job.queue_adapter = :async # TODO: Configure :resque

sample.env

@@ -15,10 +15,13 @@ BIGBLUEBUTTON_SECRET=
 #   E.g. postgres://postgres:password@postgres:5432/greenlight-v3-production
 DATABASE_URL=
 
-### REDIS CACHE URL
-# Must be in the format redis://host:port
+### REDIS CACHE
+# REDIS_URL: Must be in the format redis://host:port
 #   E.g. redis://redis:6379
+# REDIS_SENTINEL: Must be an array of host, port pairs. In this case leave REDIS_URL blank or set it to e.g. redis://mymaster.
+#   E.g. [{host: 'host1', port: 26379}, {host: 'host2', port: 26379}, {host: 'host3', port: 26379}]
 REDIS_URL=
+REDIS_SENTINEL=
 
 ### OPTIONAL ENV VARS