Calling dynamically loaded libraries is very fast, no more than a few nanoseconds per message that passes between the server and a module. It is no worse than

Calling dynamically loaded libraries is very fast, no more than a few nanoseconds per message that passes between the server and a module. It is no worse than the dynamically-linked C standard library we use so heavily. Development effort is probably the real reason. It takes a fair amount of planning to design a table-driven module loader and indirection layer. Indirection with raw pointers costs brain power. (And do not even think about the reference counting hell of a dynamically unloadable module.) Edit: And think about what happens when you upgrade a Django or Rails plug-in: it generally gets recompiled and what amounts to relinked. The difference is that the language system itself hides the work, while nginx uses explicit build tools.