Command line utility to display app status in a given port -- useful for example for signaling successful start of an application for other pods waiting with initContainers

showstat.go

package main

import (
	"encoding/json"
	"flag"
	"fmt"
	"log"
	"net/http"
	"os"
)

type App struct {
	Name   string
	Port   int
	Status int
}

const (
	errMsg = (`ERROR: You did not specify a valid command or failed to pass the proper options. Exiting!
Use "-help" or "-h" for usage instructions.
`)
	helpMsg = (`This utility will expose the status of an application in a given HTTP port.
making easier to confirm the status from outside.

Usage:
showstat -n [ <app_name> ] -p <port_number> -s <status_code>
Examples:

$ showstat -n myappname -p 9988 -s 0
`)
)

var (
	name   = flag.String("n", "", "Name of application for which the status will be shown.")
	port   = flag.Int("p", 9988, "Port number where the application status will be displayed -- default is 9988")
	status = flag.Int("s", 0, "Status of the application: 0 = running / 1 = not running -- default is 0")
)

func main() {
	flag.Usage = func() {
		flagSet := flag.CommandLine
		fmt.Println(helpMsg)
		order := []string{"n", "p", "s"}
		for _, name := range order {
			flag := flagSet.Lookup(name)
			fmt.Printf("   -%s   ", flag.Name)
			fmt.Printf("     %s\n", flag.Usage)
		}
	}
	flag.Parse()

	if *name != "" {
		strPort := fmt.Sprintf(":%v", (*port))
		fmt.Printf("INFO: '%s' is listening on port %v with status %v", *name, *port, *status)

		http.HandleFunc("/", handler)
		http.ListenAndServe(strPort, nil)

	} else {
		fmt.Println(errMsg)
		os.Exit(2)
	}
}

func handler(w http.ResponseWriter, r *http.Request) {
	app := &App{Name: *name, Port: *port, Status: *status}
	resp, err := json.Marshal(app)
	if err != nil {
		log.Fatal("ERROR:", err)
	}
	fmt.Fprintf(w, string(resp))
}