503 if node is not active

If we get to respondStandby but we're actually not in an HA cluster, we
should instead indicate the correct status to the user. Although it
might be better to change any such behavior upstream, if any upstream
code manages this state we should still handle it correctly.

Fixes #4873

http/handler.go

@@ -2,6 +2,7 @@ package http
 
 import (
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"net"
@@ -422,13 +423,20 @@ func respondStandby(core *vault.Core, w http.ResponseWriter, reqURL *url.URL) {
 	// Request the leader address
 	_, redirectAddr, _, err := core.Leader()
 	if err != nil {
+		if err == vault.ErrHANotEnabled {
+			// Standalone node, serve 503
+			err = errors.New("node is not active")
+			respondError(w, http.StatusServiceUnavailable, err)
+			return
+		}
+
 		respondError(w, http.StatusInternalServerError, err)
 		return
 	}
 
 	// If there is no leader, generate a 503 error
 	if redirectAddr == "" {
-		err = fmt.Errorf("no active Vault instance found")
+		err = errors.New("no active Vault instance found")
 		respondError(w, http.StatusServiceUnavailable, err)
 		return
 	}