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

[Lars Marowsky-Bree]

On 2014-05-25T10:01:05, Richard Brown <rbrown at suse.de> wrote:

Hi Richard,

an excellent description - there's a career in our documentation group
for you too! ;-)

Only a few additional details:

> 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.

Actually, 'tickets' are part of pacemaker even in SLE HA itself, but
fail-over for Geo scenarios isn't supported without the Geo extension.

It should be noted that there can be multiple tickets, not just one. And
that sites can host resources that depend on tickets or none; e.g., one
could have "local" resources that don't fail-over too.

> 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.

By default, pacemaker will immediately fence nodes which host resources
which depend on a revoked ticket, to reduce the needed time before a
ticket can be re-granted elsewhere.

> 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.

There can even be multiple arbitrators if the admin is thus inclined.

> 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.

Right. Though we do have a resource agent that handles IP fail-over via
dynamic DNS updates, since ARP updates don't work across multiple
network segments.

Also, this might be best discussed on the sleha-beta list.


Regards,
    Lars

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Architect Storage/HA
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