Would you choose blue-green or canary deployment for a new model version, and why?
Reported from Capital One ML loops, and the symmetric 'both have pros and cons' answer fails it. Why model failures being statistical makes canary the default, the two cases where blue-green wins, and the entity-randomization detail that survives follow-ups.
Updated Aug 2026 · Grounded in real Forward Deployed Engineer interview loops and written to a senior-engineer editorial bar.
Reported from Capital One ML loops, and the symmetric 'both have pros and cons' answer fails it. Why model failures being statistical makes canary the default, the two cases where blue-green wins, and the entity-randomization detail that survives follow-ups.
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.