High Availability for SARK

History

HA was originally developed for a customer in South Africa and it has since proved very popular with customers who place a high value on the availability of their PBX. The goal was, and is, to provide an Asterisk-based PBX with very near 100% availability. SARK HA gets pretty close to this goal. The original SARK Version 2 offering is called sarkha but this has now been superseded as part of the V3 development by a more general purpose module called asha (Asterisk High Availability).

How it works

Asha works by using the proven standard Linux HA cluster technology to run two Asterisk servers side-by-side; one active, or primary, server and one passive, or standby, server. In the event of a failure of either Asterisk or Linux on the active server, the standby server will automatically assume control of all the resources and continue the service until such time as the primary is once again ready to assume responsibility. The time it takes to fail-over can vary depending upon how you set the Heartbeat parameters but it is quite common to have large systems (250->300 phones) set-up to fail over in under 20 seconds. That means from a hard down on the primary to being able to place outbound calls on the standby.

There are two components to the solution,-

• The regular Linux Heartbeat modules, which you can install with rpm or yum and can usually be found in the extras repo of the CentOS 5 and SME 8.0 distribution libraries.
• Asterisk and SARK specific rpms which manage the synchronisation of data between nodes and ancillary tasks such as the Asterisk watchdog task.