[9.1] Fix exceptions in index pattern conflict checks (#134231)

docs/changelog/134231.yaml

@@ -0,0 +1,6 @@
+pr: 134231
+summary: Fix unnecessary determinization in index pattern conflict checks
+area: Indices APIs
+type: bug
+issues:
+ - 133652

server/src/main/java/org/elasticsearch/cluster/metadata/MetadataIndexTemplateService.java

@@ -995,12 +995,16 @@ static Map<String, List<String>> findConflictingV2Templates(
         boolean checkPriority,
         long priority
     ) {
-        Automaton v1automaton = Regex.simpleMatchToAutomaton(indexPatterns.toArray(Strings.EMPTY_ARRAY));
+        // No need to determinize the automaton, as it is only used to check for intersection with another automaton.
+        // Determinization is avoided because it can fail or become very costly due to state explosion.
+        Automaton v1automaton = Regex.simpleMatchToNonDeterminizedAutomaton(indexPatterns.toArray(Strings.EMPTY_ARRAY));
         Map<String, List<String>> overlappingTemplates = new TreeMap<>();
         for (Map.Entry<String, ComposableIndexTemplate> entry : project.templatesV2().entrySet()) {
             String name = entry.getKey();
             ComposableIndexTemplate template = entry.getValue();
-            Automaton v2automaton = Regex.simpleMatchToAutomaton(template.indexPatterns().toArray(Strings.EMPTY_ARRAY));
+            // No need to determinize the automaton, as it is only used to check for intersection with another automaton.
+            // Determinization is avoided because it can fail or become very costly due to state explosion.
+            Automaton v2automaton = Regex.simpleMatchToNonDeterminizedAutomaton(template.indexPatterns().toArray(Strings.EMPTY_ARRAY));
             if (Operations.isEmpty(Operations.intersection(v1automaton, v2automaton)) == false) {
                 if (checkPriority == false || priority == template.priorityOrZero()) {
                     logger.debug(

server/src/test/java/org/elasticsearch/cluster/metadata/MetadataIndexTemplateServiceTests.java

@@ -2495,6 +2495,23 @@ public void testV2TemplateOverlaps() throws Exception {
         }
     }
 
+    /**
+     * test that using complex index patterns doesn't run into a too_complex_to_determinize_exception,
+     * see https://github.com/elastic/elasticsearch/issues/133652
+     */
+    public void testFindConflictingTemplates_complex_pattern() throws Exception {
+        ProjectMetadata initialProject = ProjectMetadata.builder(randomProjectIdOrDefault()).build();
+        List<String> complexPattern = new ArrayList<>();
+        for (int i = 1; i < 20; i++) {
+            complexPattern.add("cluster-somenamespace-*-app" + i + "*");
+        }
+        ComposableIndexTemplate template = ComposableIndexTemplate.builder().indexPatterns(complexPattern).build();
+        MetadataIndexTemplateService service = getMetadataIndexTemplateService();
+        ProjectMetadata project = service.addIndexTemplateV2(initialProject, false, "foo", template);
+        assertEquals(0, MetadataIndexTemplateService.findConflictingV1Templates(project, "foo", complexPattern).size());
+        assertEquals(0, MetadataIndexTemplateService.findConflictingV2Templates(project, "foo", complexPattern).size());
+    }
+
     /**
      * Tests to add two component templates but ignores both with is valid
      *