On 03/22/2011 11:26 PM, José Pablo Méndez Soto wrote:
> Hi, I am starting to play around with clustering and stuff. Can someone
> please explain what openAIS is? Or better said, what is the difference
> between OpenAIS and Corosync?
> 
> Thanks,
> 
> 
>  *José Pablo Méndez

(copied from a document I am working on)

Component; openais / corosync

OpenAIS is the heart of the cluster. All other computers operate though
this component, and no cluster component can work without it. Further,
it is shared between both Pacemaker and RHCS clusters.

In Red Hat clusters, openais is configured via the central cluster.conf
file. In Pacemaker clusters, it is configured directly in openais.conf.
As we will be building an RHCS, we will only use cluster.conf. That
said, (almost?) all openais.conf options are available in cluster.conf.
This is important to note as you will see references to both
configuration files when searching the Internet.


A Little History

There were significant changes between RHCS version 2, which we are
using, and version 3 available on EL6 and recent Fedoras.

In the RHCS version 2, there was a component called openais which
handled totem. The OpenAIS project was designed to be the heart of the
cluster and was based around the Service Availability Forum's
Application Interface Specification. AIS is an open API designed to
provide inter-operable high availability services.

In 2008, it was decided that the AIS specification was overkill for RHCS
clustering and a duplication of effort in the existing and easier to
maintain corosync project. OpenAIS was then split off as a separate
project specifically designed to act as an optional add-on to corosync
for users who wanted AIS functionality.

You will see a lot of references to OpenAIS while searching the web for
information on clustering. Understanding it's evolution will hopefully
help you avoid confusion.

-- 
Digimer
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