From a7d986e6d2a5f9351903f6e9723124db438b3b47 Mon Sep 17 00:00:00 2001
From: Liyun Xiu <xiliyun@amazon.com>
Date: Wed, 24 Jul 2024 16:50:20 +0800
Subject: [PATCH] Update changelog and add one more test case

Signed-off-by: Liyun Xiu <xiliyun@amazon.com>
---
 CHANGELOG.md                                  |  1 +
 .../indices/settings/UpdateSettingsIT.java    | 20 +++++++++++++++++--
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6aa3d7a58dda4..758ed4120ce8f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -94,6 +94,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Fix constant_keyword field type used when creating index ([#14807](https://github.com/opensearch-project/OpenSearch/pull/14807))
 - Use circuit breaker in InternalHistogram when adding empty buckets ([#14754](https://github.com/opensearch-project/OpenSearch/pull/14754))
 - Fix searchable snapshot failure with scripted fields ([#14411](https://github.com/opensearch-project/OpenSearch/pull/14411))
+- Fix update settings with null replica not honoring cluster setting bug ([#14948](https://github.com/opensearch-project/OpenSearch/pull/14948))
 
 ### Security
 
diff --git a/server/src/internalClusterTest/java/org/opensearch/indices/settings/UpdateSettingsIT.java b/server/src/internalClusterTest/java/org/opensearch/indices/settings/UpdateSettingsIT.java
index a2b8c800f4282..ae79445ce41be 100644
--- a/server/src/internalClusterTest/java/org/opensearch/indices/settings/UpdateSettingsIT.java
+++ b/server/src/internalClusterTest/java/org/opensearch/indices/settings/UpdateSettingsIT.java
@@ -835,6 +835,7 @@ private void runTestDefaultNumberOfReplicasTest(final boolean closeIndex) {
 
     public void testNullReplicaUpdate() {
         internalCluster().ensureAtLeastNumDataNodes(2);
+
         // cluster setting
         String defaultNumberOfReplica = "3";
         assertAcked(
@@ -844,7 +845,7 @@ public void testNullReplicaUpdate() {
                 .setPersistentSettings(Settings.builder().put("cluster.default_number_of_replicas", defaultNumberOfReplica))
                 .get()
         );
-
+        // create index with number of replicas will ignore default value
         assertAcked(
             client().admin()
                 .indices()
@@ -858,7 +859,7 @@ public void testNullReplicaUpdate() {
             .get()
             .getSetting("test", IndexMetadata.SETTING_NUMBER_OF_REPLICAS);
         assertEquals("2", numberOfReplicas);
-
+        // update setting with null replica will use cluster setting of replica number
         assertAcked(
             client().admin()
                 .indices()
@@ -872,12 +873,27 @@ public void testNullReplicaUpdate() {
             .get()
             .getSetting("test", IndexMetadata.SETTING_NUMBER_OF_REPLICAS);
         assertEquals(defaultNumberOfReplica, numberOfReplicas);
+
+        // Clean up cluster setting, then update setting with null replica should pick up default value of 1
         assertAcked(
             client().admin()
                 .cluster()
                 .prepareUpdateSettings()
                 .setPersistentSettings(Settings.builder().putNull("cluster.default_number_of_replicas"))
         );
+        assertAcked(
+            client().admin()
+                .indices()
+                .prepareUpdateSettings("test")
+                .setSettings(Settings.builder().putNull(IndexMetadata.SETTING_NUMBER_OF_REPLICAS))
+        );
+
+        numberOfReplicas = client().admin()
+            .indices()
+            .prepareGetSettings("test")
+            .get()
+            .getSetting("test", IndexMetadata.SETTING_NUMBER_OF_REPLICAS);
+        assertEquals("1", numberOfReplicas);
     }
 
     public void testNoopUpdate() {