app.leader() - Resilient tagging of certain instances of a Ravel app

[Ghnuberath]

Summary

When a new leader type is declared, a set of Ravel app instances connected to the same Redis server will ensure that one replica is always denoted as that leader type. If the node which is the current leader for a certain leader type fails, another one is elected to take its place (via Raft consensus).

Proposed API

leader declaration

// ... 
app.leader('typeName');
app.init() // perform leader election for 'typeName' after init (postinit).
app.listen() // leaders always start before followers

example leader usage

@prelisten({leader: 'typeName'})
myMethod () {
  // will only execute on the leader for type typeName
}