[ClusterLabs] Fwd: Multi cluster

Jan Pokorný jpokorny at redhat.com
Fri Aug 4 12:35:15 EDT 2017

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.

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