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