Your deployment updates all four regions in parallel to keep versions consistent. Argue for or against.
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What the interviewer is testing
Whether you recognise that simultaneous multi-region deployment defeats the purpose of multi-region architecture — and whether you can address the version-skew objection that motivates it.
The argument against parallel
Multi-region exists so that a failure in one region does not take down the service. A bad deployment is a failure, and deploying it everywhere at once makes it a correlated failure across every region — which is precisely the scenario the architecture was bought to prevent. You have paid for multi-region and retained a single point of failure.
This is not hypothetical: several of the most-studied cloud outages followed exactly this shape, where a configuration or software change propagated globally faster than anyone could react.
The version-skew objection, addressed
The reason teams deploy in parallel is fear of running two versions simultaneously. But that fear should already be resolved, because a rolling deployment within a single region also runs two versions at once. If your system cannot tolerate version skew, it cannot be deployed without downtime at all.
So the requirements are the same ones rolling deployment already imposes: backward-compatible schema changes, versioned event payloads, tolerant readers, and no assumption that a peer is on the same version.
Where regions genuinely differ is duration — skew lasts minutes within a region and hours across regions with bake time — so any compatibility window must be sized for the longer period.
The wave design
| Wave | Target | Bake |
|---|---|---|
| 0 | Internal / synthetic-only cell | 1 hour |
| 1 | Smallest production region | 4+ hours |
| 2 | Mid-size regions | 2 hours |
| 3 | Largest and most regulated | — |
Bake periods must be long enough for slow-burning failures — memory leaks, disk fill, scheduled jobs, cache expiry, certificate paths — which is hours, not the five minutes teams are tempted to use.
What a strong answer adds
The pipeline must be able to stop and reverse mid-sequence, leaving the estate in a mixed but functioning state. A wave plan with no abort is a slower version of the same problem.
And an honest acknowledgement of the trade: wave deployment extends lead time considerably. That should be a written decision about risk versus speed, revisited as confidence in the automated analysis grows.
Common weak answers
Choosing parallel for operational simplicity. Choosing sequential without addressing version skew, which is the objection that will be raised.