High-Availability Linux

 Reliability  Availability  Serviceability

 What are HA clusters?  High-availability clusters are groups of computers that support sever applications that can be reliably utilized with a minimum of down-time.  Utilizes redundant computers in clusters that provide service when any system components fail.

 Failover – A process by which HA clusters detect hardware or software faults and restart the application on another system without requiring administrative intervention  Emphasis on a layered approach to redundancies

 Primary software of Linux-HA is called Heartbeat  No fixed limit on nodes, allowing use with clusters of any size  Parallel resource monitoring – as with normal computing, but can shift resources from one node to another if the initial node fails  Automatically removes failed nodes from the cluster

 Integrates with many popular software packages, including: Apache, DB2, Oracle, PostgreSQL  GUI included for easier controlling and monitoring of the clusters and relevant resources

 Originally capable of only handling two nodes at a time  Did not include resource monitoring  Would later switch to a layered design implementing n-node clusters

 Project was split into various separate packages  Pacemaker – Cluster resource manager component that handles resource management and node failure  Heartbeat – Now only refers to the layer used for communication between clusters and the individual nodes of the cluster.

 Resource Agents – a standardized interface for a cluster resource, used for translating operations to a cluster and determining success or failure per process  Cluster Glue – a set of libraries, tools, and utilities for use with Heartbeat and Pacemaker; this includes everything not covered by Heartbeat (messaging), Pacemaker (resource management), Resource Agents (cluster operations)  Local Resource Manager – similar to the Pacemaker, but solely exists for one client in the cluster, and is thus not “aware” of the status of the rest of the cluster