cartservice: add an exec probe written in Go

Signed-off-by: Ahmet Alp Balkan <ahmetb@google.com>

src/cartservice/Dockerfile

@@ -1,4 +1,13 @@
+# cartservice_probe
+FROM golang:1.10 as builder
+WORKDIR /src/microservices-demo/cartservice/probe
+COPY probe/ .
+RUN go get -d ./...
+RUN go build -o /cartservice_probe .
+
+# cartservice
 FROM gcr.io/google-appengine/aspnetcore:2.1.0
+COPY --from=builder /cartservice_probe /cartservice_probe
 RUN apt update && apt install net-tools telnet
 WORKDIR /app
 COPY . .

src/cartservice/probe/README.md

@@ -0,0 +1,4 @@
+# cartservice Probe
+
+This probe makes a call to the cartservice over localhost and exits to verify
+liveness of the cartservice.

src/cartservice/probe/genproto.sh

@@ -0,0 +1,6 @@
+#!/bin/bash -e
+
+PATH=$PATH:$GOPATH/bin
+protodir=../../../pb
+
+protoc --go_out=plugins=grpc:genproto -I $protodir $protodir/demo.proto

src/cartservice/probe/main.go

@@ -0,0 +1,36 @@
+package main
+
+import (
+	"context"
+	"log"
+	"os"
+	"time"
+
+	pb "./genproto"
+
+	"google.golang.org/grpc"
+)
+
+func main() {
+	port := os.Getenv("PORT")
+	if port == "" {
+		log.Fatal("probe is executed without PORT env var")
+	}
+	log.Printf("probe executing on port %q", port)
+
+	conn, err := grpc.DialContext(context.TODO(),
+		"localhost:"+port,
+		grpc.WithInsecure(),
+		grpc.WithBlock(),
+		grpc.WithTimeout(time.Second*1))
+	if err != nil {
+		log.Fatalf("probe failed: failed to connect: %+v", err)
+	}
+	defer conn.Close()
+
+	if _, err := pb.NewCartServiceClient(conn).GetCart(context.TODO(),
+		&pb.GetCartRequest{UserId: "exec-probe-nonexistinguser"}); err != nil {
+		log.Fatalf("probe failed: failed to query: %+v", err)
+	}
+	log.Println("probe successful")
+}