feat: healthcheck (#11)

* Quick healthcheck

* Fmt

* address lint

cmd/main.go

@@ -15,6 +15,8 @@ const appName = "cdk"
 const (
 	// NETWORK_CONFIGFILE name to identify the network_custom (genesis) config-file
 	NETWORK_CONFIGFILE = "custom_network" //nolint:stylecheck
+
+	HealthzPort = 3000
 )
 
 var (
@@ -62,6 +64,13 @@ var (
 		Usage:    "Allow that config-files contains deprecated fields",
 		Required: false,
 	}
+
+	healthcheckPort = cli.Uint64Flag{
+		Name:     "healthcheckPort",
+		Usage:    "Specify port for healthcheck. Default is 3000.",
+		Required: false,
+		Value:    HealthzPort,
+	}
 )
 
 func main() {
@@ -75,6 +84,7 @@ func main() {
 		&saveConfigFlag,
 		&disableDefaultConfigVars,
 		&allowDeprecatedFields,
+		&healthcheckPort,
 	}
 	app.Commands = []*cli.Command{
 		{

cmd/run.go

@@ -5,9 +5,11 @@ import (
 	"crypto/ecdsa"
 	"fmt"
 	"math/big"
+	"net/http"
 	"os"
 	"os/signal"
 	"runtime"
+	"time"
 
 	zkevm "github.com/0xPolygon/cdk"
 	dataCommitteeClient "github.com/0xPolygon/cdk-data-availability/client"
@@ -137,6 +139,25 @@ func start(cliCtx *cli.Context) error {
 		}
 	}
 
+	// Once service component starts, enable health check.
+	go func() {
+		const timeout = 3 * time.Second
+		http.HandleFunc("/healthz", func(w http.ResponseWriter, r *http.Request) {
+			_, _ = w.Write([]byte("OK"))
+		})
+		port := cliCtx.Uint64("healthcheckPort")
+		log.Infof("Listening healthcheck on port %d\n", port)
+		srv := http.Server{
+			Addr:              fmt.Sprintf(":%d", port),
+			ReadHeaderTimeout: timeout,
+		}
+		if err := srv.ListenAndServe(); err != nil {
+			log.Errorf("Error listening on port = %v", err)
+			return
+		}
+	}()
+
+	// Blocking
 	waitSignal(nil)
 
 	return nil