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main.go
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main.go
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package main
import (
"context"
"encoding/json"
"flag"
"io/ioutil"
"log"
"net/http"
"os"
"os/signal"
"syscall"
"time"
"github.com/gin-gonic/gin"
)
var version = os.Getenv("VERSION")
var backend string
func main() {
port := ":8080"
backend = *flag.String("backend-service", "http://gke-monorepo-backend:8080", "hostname of backend server")
flag.Parse()
log.Printf("Frontend version: %s\n", version)
r := gin.Default()
r.LoadHTMLGlob("templates/*")
r.GET("/", handleIndex)
r.GET("/version", handleVersion)
r.GET("/healthz", handleHealthz)
srv := &http.Server{
Addr: port,
Handler: r,
}
go func() {
if err := srv.ListenAndServe(); err != nil && err != http.ErrServerClosed {
log.Fatalf("listen: %s\n", err)
}
}()
// Wait for interrupt signal to gracefully shutdown the server with
// a timeout of 5 seconds.
quit := make(chan os.Signal, 1)
// kill (no param) default send syscall.SIGTERM
// kill -2 is syscall.SIGINT
// kill -9 is syscall.SIGKILL but can't be catch, so don't need add it
signal.Notify(quit, syscall.SIGINT, syscall.SIGTERM)
<-quit
log.Println("Shutting down server...")
// The context is used to inform the server it has 5 seconds to finish
// the request it is currently handling
ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
defer cancel()
if err := srv.Shutdown(ctx); err != nil {
log.Fatal("Server forced to shutdown:", err)
}
log.Println("Server exiting")
}
func handleIndex(c *gin.Context) {
// Call backend for info
resp, err := http.Get(backend)
if err != nil {
c.String(http.StatusInternalServerError, "Request to backend server ()%s failed:\n%v", backend, err)
return
}
defer resp.Body.Close()
body, err := ioutil.ReadAll(resp.Body)
if err != nil {
c.String(http.StatusInternalServerError, "Unable to read body from backend request:\n%v", err)
return
}
var p PodMetadata
log.Println(p)
err = json.Unmarshal([]byte(body), &p)
if err != nil {
c.String(http.StatusInternalServerError, "Unable to parse JSON from backend request:\n%v", err)
return
}
c.HTML(http.StatusOK, "index.html", p)
}
func handleVersion(c *gin.Context) {
c.String(http.StatusOK, "%s", c.Value("version"))
}
func handleHealthz(c *gin.Context) {
c.String(http.StatusOK, "", "")
}
// PodMetadata represents info about an InstanceMetadata in GCE
type PodMetadata struct {
Name string
Namespace string
HostIP string
PodIP string
StartTime string
RawRequest string
}