Build an in-memory pub/sub system: subscribe, publish, then topic wildcards, then delivery guarantees
Exact-match pub/sub is a dict of lists. The round is decided at level two (wildcard matching on hierarchical topics) and at level three, when the interviewer asks what happens when a subscriber's callback throws.
Updated Sep 2026 · Grounded in real Forward Deployed Engineer interview loops and written to a senior-engineer editorial bar.
Exact-match pub/sub is a dict of lists. The round is decided at level two (wildcard matching on hierarchical topics) and at level three, when the interviewer asks what happens when a subscriber's callback throws.
Lead with where the obvious approach breaks, because that is the judgment they are screening for — most candidates jump straight to the happy path and lose the room.
Then walk the failure back through the pipeline in order, naming the one metric the customer's exec sponsor actually cares about before you propose the fix.
