Hello Jason. Thanks very much for your prompt reply. Things are clearer and I think I can simplify further...

Really we just want the same index data to be accessible in two different data centres, with H.A.

Is this a good approach...We take an approach that there is a one "master" DC/Cluster index on which read and write operations are performed. xCDR is used to push this to the other, read-only, DC/Cluster index?

My concern would be that the indices could be out of sync, at least for some amount of time.

We could mitigate this by using session affinity at the network level but does xCDR have functionality to deal with this e.g. does it have immediate push updates (or is it all run on a schedule)?

Thanks again