Every MERN application is a network program: the Express 24,430 server, MongoDB 1,815 driver and Next.js 10,514 renderer ahead all reach the same Node modules, and when a request hangs the stack trace points there.
The modules stack cleanly: node:net wraps libuv's TCP handles as a duplex stream per connection, node:http adds llhttp — a C parser — on top of a net.Server, node:https is node:http over a node:tls socket, and node:http2 is a separate implementation built on nghttp2. Outbound, the global fetch() comes from undici 7,705 . Express is the subject of Express.js.
