From 304db100b382f0c1d1d9999dfe8ca77d1ac901c9 Mon Sep 17 00:00:00 2001
From: Yandi Lee <41042306+littlepangdi@users.noreply.github.com>
Date: Mon, 8 Jul 2024 17:05:26 +0800
Subject: [PATCH] fix(gateway client): Fix nil pointer dereference panic when
 using ruler in ring mode (#13436)

Fixes gateway client return with nil pointer panic when using ring mode for ruler service.

`clients.dnsProvider` will only be init when using `simple mode` here: https://github.com/grafana/loki/blob/183406570411a5ad5ceaf32bf07451b8fce608c1/pkg/indexgateway/client.go#L184

Service like `ruler` using `ring mode`  will run into panic `nil pointer reference` during restarting or exiting:
---
 pkg/indexgateway/client.go | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/pkg/indexgateway/client.go b/pkg/indexgateway/client.go
index 3d4abd0e79a1..b5e05b7e26ec 100644
--- a/pkg/indexgateway/client.go
+++ b/pkg/indexgateway/client.go
@@ -210,7 +210,9 @@ func (s *GatewayClient) Stop() {
 	if err != nil {
 		level.Error(s.logger).Log("msg", "failed to stop index gateway connection pool", "err", err)
 	}
-	s.dnsProvider.Stop()
+	if s.cfg.Mode == SimpleMode {
+		s.dnsProvider.Stop()
+	}
 }
 
 func (s *GatewayClient) QueryPages(ctx context.Context, queries []index.Query, callback index.QueryPagesCallback) error {