Use system fs.max-files as limits instead of hard-coded value

controllers/nginx/pkg/cmd/controller/nginx.go

@@ -288,7 +288,12 @@ func (n NGINXController) OnUpdate(cmap *api.ConfigMap, ingressCfg ingress.Config
 		cfg.ServerNameHashMaxSize = serverNameHashMaxSize
 	}
 
+	// the limit of open files is per worker process
+	// and we leave some room to avoid consuming all the FDs available
+	maxOpenFiles := (sysctlFSFileMax() / cfg.WorkerProcesses) - 1024
+
 	return n.t.Write(config.TemplateConfig{
+		MaxOpenFiles:        maxOpenFiles,
 		BacklogSize:         sysctlSomaxconn(),
 		Backends:            ingressCfg.Backends,
 		PassthroughBackends: ingressCfg.PassthroughBackends,

controllers/nginx/pkg/cmd/controller/utils.go

@@ -39,6 +39,19 @@ func sysctlSomaxconn() int {
 	return maxConns
 }
 
+// sysctlFSFileMax returns the value of fs.file-max, i.e.
+// maximum number of open file descriptors
+func sysctlFSFileMax() int {
+	maxConns, err := sysctl.New().GetSysctl("fs/file-max")
+	if err != nil {
+		glog.Errorf("unexpected error reading system maximum number of open file descriptors (fs.file-max): %v", err)
+		// returning 0 means don't render the value
+		return 0
+	}
+
+	return maxConns
+}
+
 func diff(b1, b2 []byte) ([]byte, error) {
 	f1, err := ioutil.TempFile("", "a")
 	if err != nil {