Pug Template Compilation Caching in Express Serverless Functions: Cold-Start vs Warm-Invocation Trade-offs

Integration Boundary

Pug's cache option and Express's view engine integration interact at the point where a template is first rendered during a serverless function invocation. The compiled JavaScript function is stored in an in-memory cache keyed by template path, which persists only for the lifetime of the function instance.

Goal and Constraints

The objective is to minimize per-invocation CPU time—and therefore cost—for a low-traffic workload that experiences frequent cold starts. Enabling cache: true avoids recompilation on subsequent renders within the same warm instance, but the first invocation after a cold start still pays the full compilation cost. Pre-compiling templates at startup via pug.compile() can shift that cost to a controlled warm-up phase, yet the Express view engine does not expose a direct hook to inject pre-compiled functions into its internal cache.

Open Questions

• Does Express's Pug integration reuse a pre-compiled function if it is attached to app.locals or passed through res.locals, or does it always invoke its own compilation path?
• When cache: true is set, is the compiled function stored per-process or per-request, and how does that behave under concurrent invocations in a single-instance serverless container?
• Is there a supported pattern to prime the cache during a dedicated warm-up invocation without serving a real request?