How to run two applications on one port?

It is not possible to directly run two different applications on the same TCP port because a port can be occupied by only one process. However, there are several approaches to bypass this limitation:

1. Use a reverse proxy — run a proxy server (for example, Nginx or an embedded Go HTTP reverse proxy) that listens on the required port and routes requests to different applications running on different internal ports.

2. Multiplex protocols — if applications use different protocols or can distinguish requests, you can write a demultiplexer application that accepts all connections on one port and redirects them based on the content.

3. Use Unix domain sockets or other IPC — if applications need to interact, you can run one application on a port and another on a socket, and configure the interaction.

Example with reverse proxy in Go:

package main

import (
    "log"
    "net/http"
    "net/http/httputil"
    "net/url"
)

func main() {
    target1, _ := url.Parse("http://localhost:8081")
    target2, _ := url.Parse("http://localhost:8082")

    proxy1 := httputil.NewSingleHostReverseProxy(target1)
    proxy2 := httputil.NewSingleHostReverseProxy(target2)

    http.HandleFunc("/app1/", func(w http.ResponseWriter, r *http.Request) {
        r.URL.Path = r.URL.Path[len("/app1"):]
        proxy1.ServeHTTP(w, r)
    })

    http.HandleFunc("/app2/", func(w http.ResponseWriter, r *http.Request) {
        r.URL.Path = r.URL.Path[len("/app2"):]
        proxy2.ServeHTTP(w, r)
    })

    log.Println("Starting proxy on :8080")
    log.Fatal(http.ListenAndServe(":8080", nil))
}

Here, the proxy listens on port 8080 and redirects requests with prefixes /app1/ and /app2/ to different applications running on 8081 and 8082.