115 Leader and Follower (New) PDF

115 Leader and Follower (New) Let's learn about the leader and follower patterns and its usage in distributed *** *** systems. Background * Distributed systems keep multiple copies of data for fault tolerance and higher...

115 Leader and Follower (New) Let's learn about the leader and follower patterns and its usage in distributed *** *** systems. Background * Distributed systems keep multiple copies of data for fault tolerance and higher * * * * * * availability. * A system can use quorum to ensure data consistency between replicas, i.e., all reads *** *** * * * * and writes are not considered successful until a majority of nodes participate in the operation. * However, using quorum can lead to another problem, that is, lower availability; * ** ** at any time, the system needs to ensure that at least a majority of replicas are up and available, otherwise the operation will fail. *** Quorum is also not sufficient, as in certain failure scenarios, the client can still *** see inconsistent data. Solution Allow only a single server (called the leader) to be responsible for data replication *** ~ ~ *** * * ** ** * and to coordinate work. * *** *** *** At any time, one server is elected as the leader. *** This leader becomes responsible for data replication and can act as the central *** *** *** point for all coordination. *** *** The followers only accept writes from the leader and serve as a backup. *** *** In case the leader fails, one of the followers can become the leader. *** In some cases, the follower can serve read requests for load balancing. [Leader entertains requests from the client and is responsible for replicating and ~ coordinating with followers] ~