You inherit 200 Jenkins jobs with no documentation and are asked to migrate to a modern CI system. How do you approach it?
What they are really testing: Migration judgement. The failure mode is a big-bang rewrite, and the strongest answers begin by discovering what is actually still used rather than by porting everything.
A real interview question
You inherit 200 Jenkins jobs with no documentation and are asked to migrate to a modern CI system. How do you approach it?
What most people say
drag me
“Port all 200 jobs to the new system, then switch over on a chosen date.”
A big-bang migration of undocumented jobs is how these projects die: it takes months with no value delivered, ports dead jobs faithfully, and the cutover concentrates all risk into one day.
The follow-ups they ask next
A job is undocumented and nobody claims it, but it runs nightly. What do you do?
Do not just delete it. Trace what it writes to and who consumes that. If still unclear, disable it and see who complains within a couple of cycles, having confirmed you can restore it quickly.
How do you keep teams from stalling on the old system?
Make the new path better, not just mandated: faster, self-service, better logs. Then a deadline plus help migrating. Mandate without improvement produces resentment and workarounds.
What the interviewer is listening for
- Discovers usage before porting
- Builds the template first
- Sets a real decommission date
What sinks the answer
- Big-bang cutover
- Ports dead jobs
- No parallel-run verification
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 would [find which jobs actually ran in 90 days, since many will be dead], [classify into delete, template, and genuinely complex], [build the shared template on 2 services first], then [migrate incrementally with both running in parallel]. And [set a hard decommission date] or the old system lives forever.”
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