Octopus is a gem that makes it easy to setup database replication (primary/follower) & sharding in Rails.
When using Octopus with Unicorn, we need to make a couple configuration changes to ensure our additional DB connections are established before users start hitting our app.
First, we need to initialize the DB connections in our after_fork block.
after_fork do |server, worker| Octopus.config['production']['master'] = ActiveRecord::Base.connection.config ActiveRecord::Base.connection.initialize_shards(Octopus.config) end
Then in our before_fork, we need to drop all connections.
before_fork do |server, worker| if defined?(ActiveRecord::Base) shards = ActiveRecord::Base.connection_proxy.instance_variable_get(:@shards) shards.each do |shard, connection_pool| connection_pool.disconnect! end ActiveRecord::Base.connection.disconnect! end end
Look here for a full example of this being used.
That’s it! With those two minor changes, Unicorn will properly establish and close our additional DB connections.