DEV: Install `rails_failover` gem to test our Redis changes.

Gemfile

@@ -248,3 +248,5 @@ end
 gem 'webpush', require: false
 gem 'colored2', require: false
 gem 'maxminddb'
+
+gem 'rails_failover', require: false

Gemfile.lock

@@ -277,6 +277,8 @@ GEM
       nokogiri (>= 1.6)
     rails-html-sanitizer (1.3.0)
       loofah (~> 2.3)
+    rails_failover (0.1.0)
+      redis (~> 4)
     rails_multisite (2.1.2)
       activerecord (> 5.0, < 7)
       railties (> 5.0, < 7)
@@ -509,6 +511,7 @@ DEPENDENCIES
   rack (= 2.2.2)
   rack-mini-profiler
   rack-protection
+  rails_failover
   rails_multisite
   railties (= 6.0.3)
   rake

app/models/global_setting.rb

@@ -164,9 +164,15 @@ class GlobalSetting
         c[:port] = redis_port if redis_port
 
         if redis_slave_host && redis_slave_port
-          c[:slave_host] = redis_slave_host
-          c[:slave_port] = redis_slave_port
-          c[:connector] = DiscourseRedis::Connector
+          if ENV["RAILS_FAILOVER"]
+            c[:replica_host] = redis_slave_host
+            c[:replica_port] = redis_slave_port
+            c[:connector] = RailsFailover::Redis::Connector
+          else
+            c[:slave_host] = redis_slave_host
+            c[:slave_port] = redis_slave_port
+            c[:connector] = DiscourseRedis::Connector
+          end
         end
 
         c[:password] = redis_password if redis_password.present?
@@ -188,9 +194,15 @@ class GlobalSetting
         c[:port] = message_bus_redis_port if message_bus_redis_port
 
         if message_bus_redis_slave_host && message_bus_redis_slave_port
-          c[:slave_host] = message_bus_redis_slave_host
-          c[:slave_port] = message_bus_redis_slave_port
-          c[:connector] = DiscourseRedis::Connector
+          if ENV["RAILS_FAILOVER"]
+            c[:replica_host] = message_bus_redis_slave_host
+            c[:replica_port] = message_bus_redis_slave_port
+            c[:connector] = RailsFailover::Redis::Connector
+          else
+            c[:slave_host] = message_bus_redis_slave_host
+            c[:slave_port] = message_bus_redis_slave_port
+            c[:connector] = DiscourseRedis::Connector
+          end
         end
 
         c[:password] = message_bus_redis_password if message_bus_redis_password.present?

config/initializers/001-redis.rb

@@ -4,3 +4,20 @@ if Rails.env.development? && ENV['DISCOURSE_FLUSH_REDIS']
   puts "Flushing redis (development mode)"
   Discourse.redis.flushdb
 end
+
+if ENV['RAILS_FAILOVER']
+  require 'rails_failover'
+
+  message_bus_keepalive_interval = MessageBus.keepalive_interval
+
+  RailsFailover::Redis.register_master_up_callback do
+    MessageBus.keepalive_interval = message_bus_keepalive_interval
+    Discourse.clear_readonly!
+    Discourse.request_refresh!
+  end
+
+  RailsFailover::Redis.register_master_down_callback do
+    # Disables MessageBus keepalive when Redis is in readonly mode
+    MessageBus.keepalive_interval = 0
+  end
+end