wfe: Add healthz endpoint (#8484)

Deployment suggestion: If currently using the `build` endpoint for
health checks, change it to `health`.

Fixes #8476

Author: jprenken

test/integration/wfe_test.go

@@ -6,7 +6,9 @@ import (
 	"io"
 	"net/http"
 	"testing"
+	"time"
 
+	"github.com/letsencrypt/boulder/core"
 	"github.com/letsencrypt/boulder/test"
 )
 
@@ -50,3 +52,22 @@ func TestWFEHTTPMetrics(t *testing.T) {
 	test.AssertContains(t, string(body), `response_time_count{code="200",endpoint="/directory",method="GET"}`)
 	resp.Body.Close()
 }
+
+// TestWFEHealthz checks to make sure that the /health endpoint returns 200 OK,
+// retrying in case overrides take a moment to load.
+func TestWFEHealthz(t *testing.T) {
+	retries := 0
+	var status int
+	for retries < 5 {
+		time.Sleep(core.RetryBackoff(retries, time.Millisecond*2, time.Millisecond*50, 2))
+		resp, err := http.Get("http://boulder.service.consul:4001/healthz")
+		test.AssertNotError(t, err, "GET boulder-wfe2 healthz")
+		status = resp.StatusCode
+		resp.Body.Close()
+		if status == http.StatusOK {
+			break
+		}
+		retries++
+	}
+	test.AssertEquals(t, status, http.StatusOK)
+}

wfe2/wfe.go

@@ -71,6 +71,7 @@ const (
 	getCertPath     = "/get/cert/"
 	getCertInfoPath = "/get/certinfo/"
 	buildIDPath     = "/build"
+	healthzPath     = "/healthz"
 )
 
 const (
@@ -425,6 +426,7 @@ func (wfe *WebFrontEndImpl) Handler(stats prometheus.Registerer, oTelHTTPOptions
 	wfe.HandleFunc(m, getCertPath, wfe.Certificate, "GET")
 	wfe.HandleFunc(m, getCertInfoPath, wfe.CertificateInfo, "GET")
 	wfe.HandleFunc(m, buildIDPath, wfe.BuildID, "GET")
+	wfe.HandleFunc(m, healthzPath, wfe.Healthz, "GET")
 
 	// Endpoint for draft-ietf-acme-ari
 	if features.Get().ServeRenewalInfo {
@@ -1801,6 +1803,31 @@ func (wfe *WebFrontEndImpl) BuildID(ctx context.Context, logEvent *web.RequestEv
 	}
 }
 
+type WfeHealthzResponse struct {
+	Details string
+}
+
+// Healthz tells the requester whether we're ready to serve requests.
+func (wfe *WebFrontEndImpl) Healthz(ctx context.Context, logEvent *web.RequestEvent, response http.ResponseWriter, request *http.Request) {
+	status := http.StatusOK
+	details := "OK"
+
+	if !wfe.txnBuilder.Ready() {
+		status = http.StatusServiceUnavailable
+		details = "waiting for overrides"
+	}
+
+	jsonResponse, err := json.Marshal(WfeHealthzResponse{Details: details})
+	if err != nil {
+		wfe.log.Warningf("Could not marshal healthz response: %s", err)
+	}
+
+	err = wfe.writeJsonResponse(response, logEvent, status, jsonResponse)
+	if err != nil {
+		wfe.log.Warningf("Could not write response: %s", err)
+	}
+}
+
 // Options responds to an HTTP OPTIONS request.
 func (wfe *WebFrontEndImpl) Options(response http.ResponseWriter, request *http.Request, methodsStr string, methodsMap map[string]bool) {
 	// Every OPTIONS request gets an Allow header with a list of supported methods.

wfe2/wfe_test.go

@@ -1095,6 +1095,11 @@ func TestHTTPMethods(t *testing.T) {
 			Path:    buildIDPath,
 			Allowed: getOnly,
 		},
+		{
+			Name:    "Health path should be GET only",
+			Path:    healthzPath,
+			Allowed: getOnly,
+		},
 		{
 			Name:    "Rollover path should be POST only",
 			Path:    rolloverPath,