[ClusterLabs] Fwd: Multi cluster

[Jan Pokorný]

[addendum inline]

On 04/08/17 18:35 +0200, Jan Pokorný wrote:
> On 03/08/17 20:37 +0530, sharafraz khan wrote:
>> I am new to clustering so please ignore if my Question sounds silly, i have
>> a requirement were in i need to create cluster for ERP application with
>> apache, VIP component,below is the scenario
>> 
>> We have 5 Sites,
>> 1. DC
>> 2. Site A
>> 3. Site B
>> 4. Site C
>> 5. Site D
>> 
>> Over here we need to configure HA as such that DC would be the primary Node
>> hosting application & be accessed from by all the users in each sites, in
>> case of Failure of DC Node, Site users should automatically be switched to
>> there local ERP server, and not to the Nodes at other sites, so
>> communication would be as below
>> 
>> DC < -- > Site A
>> DC < -- > Site B
>> DC < -- > Site C
>> DC < -- > Site D
>> 
>> Now the challenge is
>> 
>> 1. If i create a cluster between say DC < -- > Site A it won't allow me to
>> create another cluster on DC with other sites
>> 
>> 2. if i setup all the nodes in single cluster how can i ensure that in case
>> of Node Failure or loss of connectivity to DC node from any site, users
>> from that sites should be switched to Local ERP node and not to nodes on
>> other site.
>> 
>> a urgent response and help would be quite helpful
> 
> From your description, I suppose you are limited to just a single
> machine per site/DC (making the overall picture prone to double
> fault, first DC goes down, then any of the sites goes down, then
> at least the clients of that very site encounter the downtime).
> Otherwise I'd suggest looking at booth project that facilitates
> inter-cluster (back to your "multi cluster") decisions, extending
> upon pacemaker performing the intra-cluster ones.
> 
> Using a single cluster approach, you should certainly be able to
> model your fallback scenario, something like:
> 
> - define a group A (VIP, apache, app), infinity-located with DC
> - define a different group B with the same content, set up as clone
>   B_clone being (-infinity)-located with DC
> - set up ordering "B_clone starts when A stops", of "Mandatory" kind
> 
> Further tweaks may be needed.

Hmm, actually VIP would not help much here, even if "ip" adapted per
host ("#uname") as there're two conflicting principles ("globality"
of the network for serving from DC vs. locality when serving from
particular sites _in parallel_).  Something more sophisticated would
likely be needed.

-- 
Poki
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