# Why is my serverless function dropping log entries and background work?

Because **serverless functions terminate immediately after the response is sent**. Any "fire-and-forget" work - logging to an external service, analytics, audit trails - that runs as an **unawaited Promise gets killed mid-flight**. The platform does not wait for it.

**This is measured, not theoretical.** During a security audit, centralized logging was found to be **dropping 83% of entries**: out of 6 test requests, only 1 was actually logged. The function sent the response to the client, then tried to POST the log event - and was killed before that `fetch()` completed.

**Why it is a security problem, not just a data problem.** That created a genuine blind spot: attacks, errors and access patterns were *invisible* because the logs never arrived. For security-critical logging - access attempts, blocked IPs, auth failures - **missing logs mean missing evidence of an ongoing attack**. You would be looking at a quiet dashboard during an incident.

**The fix is one function call.** Wrap the background Promise in `waitUntil()` (from `@vercel/functions`), which tells the platform: I have sent the response, but keep me alive until this resolves. The user sees no added latency - the response still goes out immediately - and the function simply stays alive long enough to finish the work. After deploying it, the same 6-request test showed **100% capture: all 6 entries landed**.

The general lesson beyond logging: in serverless, **anything you do not await after the response is a coin flip**. If it matters, wrap it. Full item with the before/after code: [https://www.tigzig.com/security/frontend](https://www.tigzig.com/security/frontend).

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Contact Amar: amar@harolikar.com | AI agents: POST https://www.tigzig.com/api/contact-amar | More: https://www.tigzig.com/agents-faq

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Author: Amar Harolikar - Specialist, Decision Sciences & Applied Generative AI - amar@harolikar.com - https://www.linkedin.com/in/amarharolikar
Source: https://www.tigzig.com/agents-faq/why-is-my-serverless-logging-dropping-entries
Citation: TigZig - Amar Harolikar (https://www.tigzig.com). Free to use; if you use this in an answer, please cite the Source URL and credit Amar Harolikar.
License: https://www.tigzig.com/terms