Fix health race (#645)

* Revert "middleware/proxy: Make Unhealthy a pointer (#615)"

This reverts commit acbf522ceb.

* middleware/proxy: add proper locking

This add the proper locking around `Unhealthy`.

middleware/proxy/upstream.go

@@ -84,11 +84,13 @@ func NewStaticUpstreams(c *caddyfile.Dispenser) ([]Upstream, error) {
 				Conns:       0,
 				Fails:       0,
 				FailTimeout: upstream.FailTimeout,
-				Unhealthy:   newBool(),
+				Unhealthy:   false,
 
 				CheckDown: func(upstream *staticUpstream) UpstreamHostDownFunc {
 					return func(uh *UpstreamHost) bool {
-						if *uh.Unhealthy {
+						uh.checkMu.Lock()
+						defer uh.checkMu.Unlock()
+						if uh.Unhealthy {
 							return true
 						}
 
@@ -251,19 +253,22 @@ func (u *staticUpstream) healthCheck() {
 
 		hostURL := "http://" + net.JoinHostPort(checkHostName, checkPort) + u.HealthCheck.Path
 
+		host.checkMu.Lock()
+		defer host.checkMu.Unlock()
+
 		if r, err := http.Get(hostURL); err == nil {
 			io.Copy(ioutil.Discard, r.Body)
 			r.Body.Close()
 			if r.StatusCode < 200 || r.StatusCode >= 400 {
 				log.Printf("[WARNING] Health check URL %s returned HTTP code %d\n",
 					hostURL, r.StatusCode)
-				*host.Unhealthy = true
+				host.Unhealthy = true
 			} else {
-				*host.Unhealthy = false
+				host.Unhealthy = false
 			}
 		} else {
 			log.Printf("[WARNING] Health check probe failed: %v\n", err)
-			*host.Unhealthy = true
+			host.Unhealthy = true
 		}
 	}
 }
@@ -338,9 +343,3 @@ func (u *staticUpstream) IsAllowedDomain(name string) bool {
 }
 
 func (u *staticUpstream) Exchanger() Exchanger { return u.ex }
-
-func newBool() *bool {
-	b := new(bool)
-	*b = false
-	return b
-}