1) We actually keep the "state" for slave/master in EC2 tags, which are changed via a different mechanism. 2) There's a different configuration for mapping whi

1) We actually keep the "state" for slave/master in EC2 tags, which are changed via a different mechanism. 2) There's a different configuration for mapping which database hosts exist on which shard. Our system currently has multiple database shards per machine, and that's stored in a configuration that our automation will update when new machines/shards go into production.