A health middleware

Start http handler on port 8080 and return OK. Also add some

documentation fixes for the prometheus middleware.

core/directives.go

@@ -45,6 +45,7 @@ var directiveOrder = []directive{
 	{"root", setup.Root},
 	{"bind", setup.BindHost},
 	{"tls", https.Setup},
+	{"health", setup.Health},
 
 	// Other directives that don't create HTTP handlers
 	{"startup", setup.Startup},

core/setup/health.go

@@ -0,0 +1,33 @@
+package setup
+
+import (
+	"github.com/miekg/coredns/middleware"
+	"github.com/miekg/coredns/middleware/health"
+)
+
+func Health(c *Controller) (middleware.Middleware, error) {
+	addr, err := parseHealth(c)
+	if err != nil {
+		return nil, err
+	}
+
+	h := health.Health{Addr: addr}
+	c.Startup = append(c.Startup, h.ListenAndServe)
+	return nil, nil
+}
+
+func parseHealth(c *Controller) (string, error) {
+	addr := ""
+	for c.Next() {
+		args := c.RemainingArgs()
+
+		switch len(args) {
+		case 0:
+		case 1:
+			addr = args[0]
+		default:
+			return "", c.ArgErr()
+		}
+	}
+	return addr, nil
+}

core/setup/prometheus.go

@@ -9,7 +9,7 @@ import (
 
 const (
 	path = "/metrics"
-	addr = "localhost:9135" // 9153 is occopied by bind_exporter
+	addr = "localhost:9135" // 9153 is occupied by bind_exporter
 )
 
 var once sync.Once