availability patterns

• two patterns to support high availability.
  • failover.
    • master slave pattern.
      • heartbeats are sent between the active server and the passive server that’s on standby.
      • when the heartbeat is interrupted, the passive server takes over as the active server.
    • active-active (a.k.a. master-master).
      • both servers are running and spreading the load.
    • disadvantages.
      • adds more hardware and complexity.
      • potential for lost data is the active system fails while replicating data to the passive.
  • replication.
    • similar idea to database-replication.
    • single-leader-replication or multi-leader-replication.