High Availability

On-demand failover makes applications highly available

The Red Hat® Enterprise Linux® High Availability Add-On provides on-demand failover to make applications highly available. It delivers continuous availability of services by eliminating single points of failure.



Red Hat Enterprise Linux High Availability LogoConfigure the High Availability Add-On for most applications that use customizable agents and for virtual guests. By offering failover services between nodes within a cluster, this Add-On supports high availability for up to 16 nodes. (Currently this capability is limited to a single LAN or datacenter located within one physical site.)

The High Availability Add-On also enables failover for off-the-shelf applications, like Apache, MySQL, and PostgreSQL. Any of which can be coupled with resources like IP-address and single-node file systems to form highly available services. You can also easily extend the Add-On to any user-specified application that's controlled by an init script per UNIX System V (SysV) standards.

How it works

When using the High Availability Add-On, a highly available service can perform a failover from one node to another with no apparent interruption to cluster clients.

The Add-On also ensures absolute data integrity when one cluster node takes over control of a service from another cluster node. It achieves this by promptly evicting nodes from the cluster that are deemed to be faulty using a method called fencing, which prevents data corruption. The High Availability Add-On supports several types of fencing, including both power-based and storage area network (SAN)-based fencing.


Clustering, fencing, and unfencing


The High Availability Add-On enables applications to be highly available by reducing downtime and ensuring that there's no single point of failure in a cluster. It also isolates unresponsive applications and nodes so they can't corrupt critical enterprise data.

Fencing and unfencing

The High Availability Add-On provides fencing capabilities, removing access to resources from a cluster node that has lost contact with the cluster, thereby protecting resources, like shared storage, from uncoordinated modification.

After SAN-based fencing and reboot of the fenced node by an administrator, the node can unfence itself upon joining the cluster. It can then access storage without any further administrative intervention.

Rich GUI for cluster management and administration

The Conga application of Red Hat Enterprise Linux provides centralized configuration and management for the High Availability Add-On. In Red Hat Enterprise Linux 6, the web interface to luci has been redesigned and runs on TurboGears2, which provides a rich GUI-based cluster management and administration utility.

Unified logging and debugging

System administrators can now enable, capture, and read cluster system logs via a single cluster configuration command.

Cluster virtual machines

Virtualization is pervasive throughout today's enterprise datacenters. Not only is Red Hat Enterprise Linux designed to be a superior guest on any of the major hypervisors, it can also be a virtualization host.

Virtualization is integrated directly into the Red Hat Enterprise Linux kernel using Kernel-based Virtual Machine (KVM) technology. As part of the kernel, your administrators get the complete breadth of Red Hat Enterprise Linux system management, and security tools and certifications.

And now, you can run virtualized KVM guests as managed services.


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Purchasing guide

Read our purchasing guide for information on how to purchase Red Hat Enterprise Linux Add-Ons.