[sles-beta] GEO Clusters, where to get basic information

[Darren Thompson]

Richard

A very detailed and informative answer; Thank you.

Darren


On 25 May 2014 18:01, Richard Brown <rbrown at suse.de> wrote:

> On 2014-05-25 09:15, Darren Thompson wrote:
>
>> Team
>>
>> I have been using SLES HA for some time but have no exposure to SLES
>> GEO Clusters.
>>
>> Where is a good source of "basic/orientation' information for someone
>> familiar with HA but no exposure to GEO?
>>
>
> The manual is pretty good :) https://www.suse.com/documentation/sle_ha/
> singlehtml/book_sleha/book_sleha.html#cha.ha.geo
>
>  What is it?
>>
>
> GEO is an Extension to the SLE HA Extension, which enables you to build 'A
> Cluster of Clusters' spread across large Geographic distances (Separate
> Cities/States/Countries/Continents) with services being started/stopped
> on the separate cluster based on the network availability (or lack thereof)
> of the other locations.
>
>  What are it's use cases and where should it NOT bet used?
>>
>
> Its typical use case is 'Disaster Recovery' or 'Business Continuity'. A
> cluster at Site A also has its HA resources and data replicated/mirrored at
> Site B which is many miles away (eg. over 30km) with high latency
> connection (eg over 15ms, too high for 'traditional' HA Local or Metro Area
> clusters). In the event of Site A 'failing', all of the resources that
> usually 'live' at Site A can be started at Site B, providing your business
> with a way to continue operating despite the loss of Site A.
>
> It probably shouldn't be used when you're clusters are on the same local
> subnet and/or when latency is sufficiently low to make Metro clustering
> viable - why complicate matters if a simple option is available?
>
>  What is the basic principle on which it operates?
>>
>
> GEO introduces the concept of 'Tickets' - Tickets are tokens which can be
> granted/revoked from a Cluster, and used as a dependency for the operation
> of Cluster Resources. eg. a ticket called TicketA might be required by all
> the Resources that are typically at Site A. When the Ticket is revoked from
> Site A and granted to the Cluster at Site B, Site B is then the only
> cluster able to operate the services that rely on TicketA's presence. The
> distribution of Tickets is handled by a piece of software called the 'booth'
>
> Booth is an agent which runs on each cluster, and is configured to be
> aware of the other sites involved in your Geo cluster. Using UDP, it's
> designed to work in high latency environments. Booth usually has long
> expiration times on Tickets, given significant protection against brief
> connectivity issues. This comes at the potential expense of taking longer
> before automatically failing over, but this isn't the sort of thing you'd
> want the software to make a mistake about - more rapid allocation of
> tickets can of course be done by sysadmins.
>
> Arbitrators are special machines running Booth but not running HA
> Clusters. This allows you to avoid split brain scenarios by having a 3rd
> independent server arbitrate about the status of the other Sites.
> Arbitrators are not necessary if you have an odd number of Clusters in your
> Geo Cluster.
> Taking my simple 2 site example from earlier, if Sites A and B can't
> communicate with each other, there is no way Booth on either cluster can
> automatically figure out which site is operational. An arbitrator running
> elsewhere however should be able to provide enough information to determine
> whether Site A or B is 'down' or that both sites are actually 'up' and it's
> just a failure of the network link between Site A and B.
>
>  Are there configuration example/templates?
>>
>
> As the details depend totally on the structure of your network and the
> local resources you want to enable for Geo clustering, templates are a
> tricky thing to provide.
> The manual has some very simple examples which should be enough to get you
> started.
>
> Best Regards,
>
> - Richard
>
> --
> -------------------------------------------------------------------
>   Richard Brown, QA Engineer
>   Phone +4991174053-361,  Fax +4991174053-483
>   SUSE LINUX Products GmbH,  Maxfeldstr. 5,  D-90409 Nuernberg
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>



-- 

Darren Thompson

Professional Services Engineer / Consultant

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Mail: darrent at akurit.com.au <steve at akurit.com.au>
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