What do fail-open and fail-closed mean?
Answer out loud or in your head first, then compare.
Answer
It's the decision about what the system does when it can't check a condition. Fail-open means it lets things through despite the problem. Fail-closed means it blocks the operation until it can be decided reliably. The names are jargon, but the problem is very practical.
If the recommendations list doesn't work, I can show an older result. If I can't confirm the right to a confidential file, I mustn't show it to everyone. With a campaign limit you have to decide what hurts more: going over budget or holding back some traffic. It's a deliberate business and technical decision, not an accidental catch that always returns approval.
Why it matters: Helps name how the system behaves during a partial failure.
Possible follow-ups: Who sets the acceptable risk, and how do you test such a mode?
How did it go? Be honest — “Not yet” puts the question on your review list.
Start with
- D-P01 · What is HTTP, and what do a request and a response look like? — Backend, data and system design
- D-P10 · What is a database transaction? — Backend, data and system design
- D-P13 · What is a message queue, and why do we use one? — Backend, data and system design
Further reading
- PostgreSQL: Transaction Isolation(opens in a new tab)Docs; accessed 22.10.2026. Isolation, locks and serialization anomalies; a good basis for working with an ORM.