High-Availability Linux
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
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
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