From 4b9846b90fd4ca977c9073e80b993a9259f70240 Mon Sep 17 00:00:00 2001
From: Rishabh Singh <6513075+findingrish@users.noreply.github.com>
Date: Thu, 10 Aug 2023 16:37:37 +0530
Subject: [PATCH] Improve exception message when DruidLeaderClient doesn't find
 leader node (#14775)

The existing exception message No known server thrown in DruidLeaderClient is unhelpful.
---
 .../java/org/apache/druid/discovery/DruidLeaderClient.java  | 6 +++++-
 .../org/apache/druid/discovery/DruidLeaderClientTest.java   | 4 +++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/server/src/main/java/org/apache/druid/discovery/DruidLeaderClient.java b/server/src/main/java/org/apache/druid/discovery/DruidLeaderClient.java
index 3bc29da40f4..d681004326c 100644
--- a/server/src/main/java/org/apache/druid/discovery/DruidLeaderClient.java
+++ b/server/src/main/java/org/apache/druid/discovery/DruidLeaderClient.java
@@ -264,7 +264,11 @@ public class DruidLeaderClient
     );
 
     if (leader == null) {
-      throw new IOE("No known server");
+      throw new IOE(
+          "A leader node could not be found for [%s] service. "
+          + "Check logs of service [%s] to confirm it is healthy.",
+          nodeRoleToWatch, nodeRoleToWatch
+      );
     } else {
       return leader;
     }
diff --git a/server/src/test/java/org/apache/druid/discovery/DruidLeaderClientTest.java b/server/src/test/java/org/apache/druid/discovery/DruidLeaderClientTest.java
index 6b8f32ba190..cff1aeb9fb0 100644
--- a/server/src/test/java/org/apache/druid/discovery/DruidLeaderClientTest.java
+++ b/server/src/test/java/org/apache/druid/discovery/DruidLeaderClientTest.java
@@ -159,7 +159,9 @@ public class DruidLeaderClientTest extends BaseJettyTest
     druidLeaderClient.start();
 
     expectedException.expect(IOException.class);
-    expectedException.expectMessage("No known server");
+    expectedException.expectMessage(
+        "A leader node could not be found for [PEON] service. "
+        + "Check logs of service [PEON] to confirm it is healthy.");
     druidLeaderClient.makeRequest(HttpMethod.POST, "/simple/direct");
   }