Build path to index.html only once

internal/upstream/deploy_page.go

@@ -8,8 +8,9 @@ import (
 )
 
 func handleDeployPage(documentRoot string, handler http.Handler) http.HandlerFunc {
+	deployPage := filepath.Join(documentRoot, "index.html")
+
 	return func(w http.ResponseWriter, r *http.Request) {
-		deployPage := filepath.Join(documentRoot, "index.html")
 		data, err := ioutil.ReadFile(deployPage)
 		if err != nil {
 			handler.ServeHTTP(w, r)