We run a customer facing web app in a single Azure region. Leadership wants it to survive a regional outage. Take me through how you would make it multi region.
What they are really testing: They are checking whether you drive the conversation with RPO and RTO instead of jumping to active active, and whether you know the database is the hard part and everything else is easy.
A real interview question
We run a customer facing web app in a single Azure region. Leadership wants it to survive a regional outage. Take me through how you would make it multi region.
What most people say
drag me
“I would deploy the same app to a second region, put Traffic Manager in front, and turn on geo replication on the database so it is active active.”
It states a topology without ever asking for an RPO or an RTO, and it calls geo replication active active, which hides the fact that writes still have a single primary and failover is not automatic or free.
The follow-ups they ask next
Why not just go active active from day one?
Point at write conflicts and cross region write latency, then say that active active is a data modelling problem, not a deployment problem, and it only pays off when the RTO is near zero.
How do you know the failover actually works?
Rehearse it on a schedule in production or in a production like environment, measure the real RTO against the target, and treat a game day that has never been run as a plan that does not exist.
What the interviewer is listening for
- Opens by asking for RPO and RTO and lets those numbers pick the topology
- Says plainly that the stateless tier is easy and the database is the hard part
- Mentions rehearsing failover rather than assuming the runbook works
- Gives a cost multiple rather than saying it will cost more
What sinks the answer
- Jumps straight to active active without asking what the business needs
- Leaves session state in application memory and never notices
- Assumes automatic database failover with no split brain discussion
- Has no plan for failing back once the primary region recovers
If you genuinely do not know
Say this instead of freezing. Reasoning out loud from what you do know beats silence every single time, and a good interviewer is listening for exactly that.
“I have not run a regional failover for real, but here is how I would reason about it. I would ask for the RPO and RTO first, duplicate the stateless tier, then spend most of my thinking on the database and on how we actually trigger and rehearse the failover.”
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