JobInterview AI

Backend Engineer interview questions

A backend interview is about what happens when things grow or fail. The hiring manager listens for how you think about data, load and failure, and for whether you have been close enough to production to have scars.

Questions to expect

  1. Describe an API or service you designed. Who called it, and what did you have to get right?

    What they listen for

    The callers and their needs first, then the contract, then what you would not let it do. Versioning and errors show experience.

  2. Tell me about a time a database became your bottleneck.

    What they listen for

    How you found the real cause, the cheapest fix you tried first, and what you measured to know it worked.

  3. How do you handle a dependency that is slow or down?

    What they listen for

    Timeouts, retries with limits, what the user sees in the meantime. A real outage you lived through is better than theory.

  4. Tell me about a data migration you ran in production.

    What they listen for

    The plan to do it without downtime, how you could go back, and what surprised you on the day.

  5. What do you look at first when a service you own gets slow?

    What they listen for

    An order of investigation you actually follow, and the dashboards or logs you rely on.

One answer, before and after

Tell me about a data migration you ran in production.

You said

We had to move to a new schema for users, so I wrote a script and we ran it one night. There were a few issues with some rows but we sorted them out, and it took longer than planned but in the end everything was migrated.

Try

I moved 12 million user rows to a new schema with no downtime. I wrote to both schemas for a week, backfilled in batches of 10,000 at night, and compared counts and checksums every morning. About 3,000 rows had malformed emails; I fixed them by rule and listed the rest for support. We switched reads on a Tuesday and kept the old table a month, in case.

The plan, the checks and the way back are what a hiring manager wants to hear.

What a report scores for this role

System design
You explain a design through its constraints, not its buzzwords.
Reliability
You say how it fails and how you would know.
Clarity
You go from the problem to the decision without a detour.

Examples: each report picks the competencies that fit the role and the interview.

Rehearse this interview out loud

Reading these questions is a start. Saying your answers to someone who follows up is the rehearsal.

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