From 68171c7a638a4087deac495b39ca7f539ed93673 Mon Sep 17 00:00:00 2001
From: Miek Gieben <miek@miek.nl>
Date: Wed, 6 Apr 2016 09:21:46 +0100
Subject: A health middleware

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

documentation fixes for the prometheus middleware.
---
 middleware/health/README.md | 21 +++++++++++++++++++++
 middleware/health/health.go | 38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 59 insertions(+)
 create mode 100644 middleware/health/README.md
 create mode 100644 middleware/health/health.go

(limited to 'middleware/health')

diff --git a/middleware/health/README.md b/middleware/health/README.md
new file mode 100644
index 000000000..3bfb5bb5f
--- /dev/null
+++ b/middleware/health/README.md
@@ -0,0 +1,21 @@
+# health
+
+This module enables a simple health check.
+
+By default it will listen on port 9180.
+
+Restarting CoreDNS will stop the health checking. This is a bug. Also [this upstream
+Caddy bug](https://github.com/mholt/caddy/issues/675).
+
+## Syntax
+
+~~~
+health
+~~~
+
+It optionally takes an address, the default is `:8080`. The health path is fixed to `/health`. It
+will just return "OK", when CoreDNS is healthy.
+
+This middleware only needs to be enabled once.
+
+## Examples
diff --git a/middleware/health/health.go b/middleware/health/health.go
new file mode 100644
index 000000000..8c1665e57
--- /dev/null
+++ b/middleware/health/health.go
@@ -0,0 +1,38 @@
+package health
+
+import (
+	"io"
+	"log"
+	"net/http"
+	"sync"
+)
+
+var once sync.Once
+
+type Health struct {
+	Addr string
+}
+
+func health(w http.ResponseWriter, r *http.Request) {
+	io.WriteString(w, ok)
+}
+
+func (h Health) ListenAndServe() error {
+	if h.Addr == "" {
+		h.Addr = defAddr
+	}
+	once.Do(func() {
+		http.HandleFunc("/health", health)
+		go func() {
+			if err := http.ListenAndServe(h.Addr, nil); err != nil {
+				log.Printf("[ERROR] Failed to start health handler: %s", err)
+			}
+		}()
+	})
+	return nil
+}
+
+const (
+	ok      = "OK"
+	defAddr = ":8080"
+)
-- 
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