initial shape of the tool

main.go

@@ -0,0 +1,82 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"net/http"
+	"net/http/httputil"
+	"net/url"
+	"os"
+	"os/signal"
+	"strings"
+
+	"tailscale.com/tsnet"
+)
+
+type upstream struct {
+	hostname string
+	port     string
+}
+
+func must[T any](t T, err error) T {
+	if err != nil {
+		panic(err)
+	}
+	return t
+}
+
+func main() {
+	var servers []*http.Server
+
+	upstreamsConfig := os.Getenv("UPSTREAMS")
+	hosts := strings.Split(upstreamsConfig, ",")
+	if upstreamsConfig == "" || len(hosts) == 0 {
+		log.Fatalf("set UPSTREAMS in environment like 'dockerhost:7400,otherdocker:80'")
+	}
+
+	for _, upstream := range hosts {
+		hostname, port, ok := strings.Cut(upstream, ":")
+		if hostname == "" {
+			// parsing error, just skip it
+			continue
+		}
+		if !ok || port == "" {
+			// default to 80
+			port = "80"
+		}
+		s := &tsnet.Server{
+			Dir:      "/.config/" + hostname,
+			Hostname: hostname,
+		}
+		defer s.Close()
+
+		ln, err := s.Listen("tcp", ":80")
+		if err != nil {
+			fmt.Printf("%+v\n", err)
+			return
+		}
+		defer ln.Close()
+
+		srv := &http.Server{
+			Handler: httputil.NewSingleHostReverseProxy(
+				must(url.Parse("http://" + hostname + ":" + port + "/")),
+			),
+		}
+		servers = append(servers, srv)
+		// start server
+		go func() {
+			err = srv.Serve(ln)
+			fmt.Printf("%+v\n", err)
+		}()
+	}
+
+	sigint := make(chan os.Signal, 1)
+	signal.Notify(sigint, os.Interrupt)
+	<-sigint
+	for _, server := range servers {
+		if err := server.Shutdown(context.Background()); err != nil {
+			log.Printf("HTTP server Shutdown: %v", err)
+		}
+	}
+}