Your team wants to build an internal developer platform. A vendor sells one. How do you decide?
What they are really testing: Commercial judgement. They want total cost of ownership thinking, differentiation reasoning, and honesty about engineers preferring to build.
A real interview question
Your team wants to build an internal developer platform. A vendor sells one. How do you decide?
What most people say
drag me
“Build it, because we understand our needs better than any vendor could.”
It is the answer engineers want and it consistently underestimates the multi-year maintenance cost. The internal platform gets built by 3 enthusiastic people, 2 of whom leave, and it becomes an unowned dependency nobody can modify.
The follow-ups they ask next
The vendor lacks one feature the team considers essential. How do you weigh that?
Ask how essential it truly is and whether it can be built alongside. One gap rarely justifies owning an entire platform, but a gap in the core workflow that cannot be extended might.
How would you avoid vendor lock-in on a platform decision?
Keep the underlying primitives open, containers, standard config, OpenTelemetry, so the vendor sits above portable foundations. Then a migration is expensive but possible rather than a rewrite.
What the interviewer is listening for
- Starts from differentiation
- Costs maintenance and opportunity cost
- Names the build bias explicitly
What sinks the answer
- Defaults to building
- Ignores ongoing maintenance
- No exit strategy from the vendor
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.
“First [does it differentiate us? Deploy tooling does not win customers], so default to buy. Cost the build [including 2 engineers maintaining it and the product work forgone], and name [the engineer bias toward building]. Check [lock-in and exit cost]. Usually the answer is [buy the commodity layers, build the thin integration], trialled on [2 teams with success criteria].”
Keep going with strategy
Principal
You join a 200-engineer company where every team built its own deployment tooling. What is your strategy?
Principal
When would you tell a company not to use Kubernetes?
Principal
The business wants faster shipping, your on-call team is burning out from incidents. How do you resolve that?
Principal
Tell me about a time you argued against your own proposal or changed your mind on a significant technical decision.
Principal
One slow dependency takes down your entire system. Why does that happen and how do you prevent it?
Principal
Design multi-region failover for a system that currently runs in one region, targeting 15 minutes recovery.
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