Adding cluster setting for search ignore unavailable

server/src/main/java/org/opensearch/action/search/TransportSearchAction.java

@@ -1080,6 +1080,10 @@ private void executeSearch(
             // No user preference defined in search request - apply cluster service default
             searchRequest.allowPartialSearchResults(searchService.defaultAllowPartialSearchResults());
         }
+        if (searchRequest.ignoreUnavailable() == null) {
+            // No user preference defined in search request - apply cluster service default
+            searchRequest.ignoreUnavailable(searchService.defaultIgnoreUnavailable());
+        }
         if (searchRequest.isSuggestOnly()) {
             // disable request cache if we have only suggest
             searchRequest.requestCache(false);

server/src/main/java/org/opensearch/common/settings/ClusterSettings.java

@@ -390,6 +390,7 @@ public void apply(Settings value, Settings current, Settings previous) {
                 ClusterManagerService.CLUSTER_MANAGER_SERVICE_SLOW_TASK_LOGGING_THRESHOLD_SETTING,
                 SearchService.DEFAULT_SEARCH_TIMEOUT_SETTING,
                 SearchService.DEFAULT_ALLOW_PARTIAL_SEARCH_RESULTS,
+                SearchService.DEFAULT_IGNORE_UNAVAILABLE,
                 TransportSearchAction.SHARD_COUNT_LIMIT_SETTING,
                 TransportSearchAction.SEARCH_CANCEL_AFTER_TIME_INTERVAL_SETTING,
                 TransportSearchAction.SEARCH_QUERY_METRICS_ENABLED_SETTING,

server/src/main/java/org/opensearch/search/SearchService.java

@@ -230,6 +230,14 @@ public class SearchService extends AbstractLifecycleComponent implements IndexEv
         Property.NodeScope
     );
 
+    // Keeping the default value to maintain existing behaviour
+    public static final Setting<Boolean> DEFAULT_IGNORE_UNAVAILABLE = Setting.boolSetting(
+        "search.default_ignore_unavailable",
+        false,
+        Property.Dynamic,
+        Property.NodeScope
+    );
+
     public static final Setting<Integer> MAX_OPEN_SCROLL_CONTEXT = Setting.intSetting(
         "search.max_open_scroll_context",
         500,
@@ -312,6 +320,8 @@ public class SearchService extends AbstractLifecycleComponent implements IndexEv
 
     private volatile boolean defaultAllowPartialSearchResults;
 
+    private volatile boolean defaultIgnoreUnavailable;
+
     private volatile boolean lowLevelCancellation;
 
     private volatile int maxOpenScrollContext;
@@ -381,6 +391,10 @@ public SearchService(
         clusterService.getClusterSettings()
             .addSettingsUpdateConsumer(DEFAULT_ALLOW_PARTIAL_SEARCH_RESULTS, this::setDefaultAllowPartialSearchResults);
 
+        defaultIgnoreUnavailable = DEFAULT_IGNORE_UNAVAILABLE.get(settings);
+        clusterService.getClusterSettings()
+            .addSettingsUpdateConsumer(DEFAULT_IGNORE_UNAVAILABLE, this::setDefaultIgnoreUnavailable);
+
         maxOpenScrollContext = MAX_OPEN_SCROLL_CONTEXT.get(settings);
         clusterService.getClusterSettings().addSettingsUpdateConsumer(MAX_OPEN_SCROLL_CONTEXT, this::setMaxOpenScrollContext);
 
@@ -453,6 +467,14 @@ public boolean defaultAllowPartialSearchResults() {
         return defaultAllowPartialSearchResults;
     }
 
+    private void setDefaultIgnoreUnavailable(boolean defaultIgnoreUnavailable) {
+        this.defaultIgnoreUnavailable = defaultIgnoreUnavailable;
+    }
+
+    public boolean defaultIgnoreUnavailable() {
+        return defaultIgnoreUnavailable;
+    }
+
     private void setMaxOpenScrollContext(int maxOpenScrollContext) {
         this.maxOpenScrollContext = maxOpenScrollContext;
     }