herokuのREDIS_URLは認証付きで複雑なのでスキーマ込みで環境変数に渡す

またredis-rbで無指定の場合の接続先も同環境変数を参照している

.env.sample

@@ -4,3 +4,4 @@ DATABASE_PASSWORD=
 SLACK_API_KEY=
 SLACK_API_SECRET=
 SLACK_OAUTH_ACCESS_TOKEN=
+REDIS_URL='redis://localhost:6379'

config/application.rb

@@ -10,7 +10,7 @@ module Answer
   class Application < Rails::Application
     # Initialize configuration defaults for originally generated Rails version.
     config.load_defaults 5.1
-    config.cache_store = :redis_store, "redis://#{Settings.redis.host}:6379/0/cache", { expires_in: 3.minutes }
+    config.cache_store = :redis_store, "#{ENV['REDIS_URL']}/0/cache", { expires_in: 3.minutes }
     # Settings in config/environments/* take precedence over those specified here.
     # Application configuration should go into files in config/initializers
     # -- all .rb files in that directory are automatically loaded.

config/initializers/sidekiq.rb

@@ -1,7 +1,7 @@
 Sidekiq.configure_server do |config|
-  config.redis = { url: "redis://#{Settings.redis.host}:6379", namespace: 'sidekiq' }
+  config.redis = { url: ENV['REDIS_URL'], namespace: 'sidekiq' }
 end
 
 Sidekiq.configure_client do |config|
-  config.redis = { url: "redis://#{Settings.redis.host}:6379", namespace: 'sidekiq' }
+  config.redis = { url: ENV['REDIS_URL'], namespace: 'sidekiq' }
 end

config/settings.yml

@@ -1,2 +0,0 @@
-redis:
-  host: 'localhost'