Ports

A web service can listen on any port, any address, however your framework does it:

http.ListenAndServe(":3000", mux)          // works
r.Run(":9000")                              // gin: works
app.Listen("localhost:4000")                // fiber, localhost only: works
http.ListenAndServe(":"+os.Getenv("PORT"), mux) // works, and skips one step

Greyship finds the port your app opened and serves it on the service's URL. HTTP, HTTP/2, WebSockets, gRPC and anything else over TCP pass through unchanged.

How it picks the portCopy Anchor Link

• PORT is always set to 8080. An app listening on 8080 on every address is reached directly.
• Otherwise Greyship waits until your app opens its ports, then serves the lowest one.
• If your app opens more than one (say 3000 for the app and 6060 for pprof), the logs say which one is served:

greyship: api listens on port 3000; serving it on its URL (it also listens on 6060, which isn't served)

If the lowest port isn't your main server (pprof on 6060, the app on 9000), read PORT for the main server so there's no doubt.

Health checkCopy Anchor Link

A web service must open a port within 30 seconds of starting, or the deploy fails:

the app didn't start listening on any port within 30s; a web service must accept connections (any port works)

Usually that means the app is stuck before ListenAndServe (waiting for a database it can't reach, for example) or it isn't a server at all; if so, make it a worker.