recommend regional over zonal clusters in K8s deployment docs

[udnay]

Yandu Oppacher (udnay) commented:

The current multi-site guides use zonal clusters for the reference implementation. These should be regional clusters to ensure proper redundancy and matching SLA requirements within a region.

e.g.

regions = {
    'us-east1-b': 'us-east1',
    'us-west1-a': 'us-west1',
    'us-central1-a': 'us-central1',
}

Would only get a customer "single instance uptime" SLA of 99.5 instead of 99.99 for regional workloads. There is similarly a lower SLA for zonal GKE clusters. We should update the docs to reflect this.

Jira Issue: DOC-1605

[udnay]

We should also look through the README for multi-region in the CRDB repo which is also out of date. /cc @keith-mcclellan

[udnay]

e.g. External LB requirement is wrong if I understand what it's trying to do, you can hit internal LB from any region in google now

[taroface]

@udnay I think I'm missing something, but based on Ben's comment in #4640, it sounds like each node needs to specify a separate AZ on start? I'm unsure how we can do that based on our STS configs, which use a single start command and specify 3 replicas. Let me know if this should be a separate issue.

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