Adding first version of HealthCheck

Added a expvar style handler for the debug http server to allow health checks (/debug/health).

Signed-off-by: Diogo Monica <diogo@docker.com>

health/api/api.go

@@ -0,0 +1,37 @@
+package api
+
+import (
+	"errors"
+	"net/http"
+
+	"github.com/docker/distribution/health"
+)
+
+var (
+	updater = health.NewStatusUpdater()
+)
+
+// DownHandler registers a manual_http_status that always returns an Error
+func DownHandler(w http.ResponseWriter, r *http.Request) {
+	if r.Method == "POST" {
+		updater.Update(errors.New("Manual Check"))
+	} else {
+		w.WriteHeader(http.StatusNotFound)
+	}
+}
+
+// UpHandler registers a manual_http_status that always returns nil
+func UpHandler(w http.ResponseWriter, r *http.Request) {
+	if r.Method == "POST" {
+		updater.Update(nil)
+	} else {
+		w.WriteHeader(http.StatusNotFound)
+	}
+}
+
+// init sets up the two endpoints to bring the service up and down
+func init() {
+	health.Register("manual_http_status", updater)
+	http.HandleFunc("/debug/health/down", DownHandler)
+	http.HandleFunc("/debug/health/up", UpHandler)
+}