use redis for cache and session store

config/environments/development.rb

@@ -19,7 +19,11 @@
   if Rails.root.join("tmp/caching-dev.txt").exist?
     config.action_controller.perform_caching = true
 
-    config.cache_store = :memory_store
+    if ENV["REDIS_CACHE_URL"] # rubocop:disable Style/ConditionalAssignment
+      config.cache_store = :redis_cache_store, { url: ENV.fetch("REDIS_CACHE_URL", nil) }
+    else
+      config.cache_store = :memory_store
+    end
     config.public_file_server.headers = {
       "Cache-Control" => "public, max-age=#{2.days.to_i}"
     }

config/environments/production.rb

@@ -51,6 +51,7 @@
 
   # Use a different cache store in production.
   # config.cache_store = :mem_cache_store
+  config.cache_store = :redis_cache_store, { url: ENV.fetch("REDIS_CACHE_URL", nil) }
 
   # Use a real queuing backend for Active Job (and separate queues per environment)
   # config.active_job.queue_adapter     = :resque

config/initializers/session_store.rb

@@ -0,0 +1,5 @@
+# frozen_string_literal: true
+
+Rails.application.config.to_prepare do
+  Rails.application.config.session_store :cache_store if ENV["REDIS_CACHE_URL"]
+end