bodyLimit: Adjusting maximum request body size for cost‑effective Fastify deployments

Goal

Reduce memory overhead on a low‑traffic Fastify server by limiting the size of incoming request bodies. A stricter bodyLimit can prevent large payloads from consuming RAM, but it must be tuned to avoid breaking legitimate traffic.

Constraints and Uncertainty

• The bodyLimit option is evaluated after decompression when fastify-compress is enabled, so the effective limit may differ for gzipped requests.
• When a request exceeds the limit, Fastify returns a 413 response before any application‑level onError hooks run, which may affect custom error handling or caching strategies.
• Streaming uploads or chunked bodies can be prematurely terminated by bodyLimit, potentially causing client errors that are hard to diagnose.

Questions

1. What is the recommended bodyLimit value for a typical low‑traffic Fastify deployment that still accommodates occasional larger payloads?
2. How does bodyLimit interact with fastify-compress when clients send gzip‑compressed bodies, and should the limit be adjusted accordingly?
3. Does the 413 response generated by bodyLimit bypass application onError hooks, and how might this affect caching or logging of oversized requests?