Red Hat Cluster Notes

1) Cluster types:
– High Availability / Failover cluster (Ideal for Database, file servers)
– Load Balancing  (Ideal for high load web traffic)
– High Performance (Large computational problems)

2) Clustering can be implemented in two ways .
– Active – Active ( Both nodes provide service , can be used for load balancing)
– Active -Passive ( At a time , only one node provides the service , can be used to provide redundancy)

3) Types of Failover:
(a) Hot Failover
(b) Warm failover
(c) Cold Failover

4) What is corosync ?
– Corosync: Provides cluster communications using the totem protocol. This the the engine that handles all communications between the cluster nodes.

5) What is fencing?
–  Concept of fencing:
When a node crashes or becomes unresponsive, it MUST be quickly powered off or blocked from accessing the shared storage device (fencing). Fencing is required, because if the cluster assumes the node has crashed, and reallocates it’s services and I/O, if the server was to wake up, it could cause havoc and possibly disk corruption. Therefore a failover device must be available so that the cluster can do STONITH – “Shoot The Other Node In The Head” – by doing an instant power off of the node.