ci/cd: create liveness probe for go mod download (#1520)

Co-authored-by: Aaron Schlesinger <70865+arschles@users.noreply.github.com>

.drone.yml

@@ -7,7 +7,9 @@ steps:
   image: golang:1.13
   commands:
     # wait for services to be ready.
-    - sleep 10
+    - cd scripts/liveness_probe
+    - go run .
+    - cd ../..
     - go mod download
     - go mod vendor # this is for when the Dockerfile gets built
   environment:
@@ -17,7 +19,6 @@ steps:
   - name: cache
     path: /go
 
-
 - name: build
   image: golang:1.13
   commands:

scripts/liveness_probe/go.mod

@@ -0,0 +1,3 @@
+module liveness_probe
+
+go 1.13

scripts/liveness_probe/main.go

@@ -0,0 +1,59 @@
+// Package main is a simple script for our CI/CD workflow
+// that ensures our sidecar proxy is running before proceeding
+package main
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"net"
+	"net/http"
+	"os"
+	"time"
+)
+
+var goproxy = os.Getenv("GOPROXY")
+
+func main() {
+	timeout := time.After(time.Minute)
+	for {
+		select {
+		case <-timeout:
+			fmt.Println("liveness probe timed out")
+			os.Exit(1)
+		default:
+		}
+		isLive, err := probe()
+		if err != nil {
+			shouldPrintErr := true
+			// connection-refused errors are expected, don't print them
+			var opErr *net.OpError
+			if errors.As(err, &opErr) && opErr.Op == "read" {
+				shouldPrintErr = false
+			}
+			if shouldPrintErr {
+				fmt.Println(err)
+			}
+		}
+		if isLive {
+			fmt.Println("proxy is live")
+			return
+		}
+		time.Sleep(time.Second)
+	}
+}
+
+func probe() (bool, error) {
+	req, err := http.NewRequest(http.MethodGet, goproxy, nil)
+	if err != nil {
+		return false, err
+	}
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+	req = req.WithContext(ctx)
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		return false, err
+	}
+	return resp.StatusCode == http.StatusOK, nil
+}