Top 5 Availability Interview Questions
Browse 5 real-world technical and behavioral interview questions about Availability. Review scenarios, edge cases, and architectural best practices.
The business says the system must be highly available. How do you turn that into a number, and what does that number cost?
Convert the phrase into an error budget over a stated window, derived from what an outage costs the business rather than from a round number of nines. Each additional nine roughly multiplies cost, because it forces redundancy, cross-region failover and operational maturity that the previous nine did not need.
You need to deploy a change to a system a running production line depends on. How is that different from a normal release?
Downtime has a per-hour cost someone can quote, so changes go in during planned windows under change control, rollback must be instant, and no staging environment reproduces a physical process. Safety functions live in separate assessed systems your software must never join. It also connects availability to the point an interviewer is testing.
Service A needs something from service B. When should that be a synchronous call and when should it be an event?
A synchronous call couples availability and latency but keeps the outcome knowable at the point of decision; an event decouples both but converts every failure into something the caller will never learn about. Choose by asking whether the caller needs the answer to proceed, not by which style is fashionable.
The line has been stopped for twenty minutes and everyone in the room believes it is your system. How do you run the next hour?
Your first deliverable is a fast, evidenced answer to whether you are in the path, measured at the station rather than on your own dashboards. Restoring production outranks diagnosis, so take a cheap evidence snapshot and then get yourself out of the path.
You promise 99.9 percent availability and you call five services that each promise the same. What have you committed to?
Nines only mean something as a downtime budget over a stated window, and dependencies in series multiply: five hard dependencies at three nines each put your own ceiling near 99.4 percent, so the target is met by removing dependencies from the critical path rather than by asking each owner for more nines.