2.13.4 Updating Server state

Clients read and update state at any of the replicated servers eg submit messages in bbs. To maintain consistency, three things are important

Multicast communication

Messages delivered to all servers in the group replicating data

Ordering of messages

Updates occur in the same ``order'' at each server

Failure recovery

When servers or the network fails, and comes back, the replicas must be able to regain consistency. Done through Voting and Transactions (later in course)