mastodon/config/cable.yml

development:
  adapter: redis
  url: redis://localhost:6379/1

test:
  adapter: async

production:
  adapter: redis
  url: redis://<%= ENV['REDIS_PASSWORD'] ? ':' + ENV['REDIS_PASSWORD'] + '@' : '' %><%= ENV['REDIS_HOST'] || 'localhost' %>:<%= ENV['REDIS_PORT'] || 6379 %>/1