[8.x] [UII] Make constant keyword backfill optional (#192921) (#192940)

# Backport

This will backport the following commits from `main` to `8.x`:
- [[UII] Make constant keyword backfill optional
(#192921)](#192921)

<!--- Backport version: 9.4.3 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sqren/backport)

<!--BACKPORT [{"author":{"name":"Jen
Huang","email":"[email protected]"},"sourceCommit":{"committedDate":"2024-09-14T02:34:46Z","message":"[UII]
Make constant keyword backfill optional (#192921)\n\n##
Summary\r\n\r\nFollow up to #188145. In some edge
cases\r\n(elastic/sdh-beats#5156), users could
override\r\nthe index template used by integration data streams. It is
possible to\r\ncreate an index template without mappings, this
causes\r\n`fillConstantKeywordValues` to receive an undefined object
when\r\nupgrading the integration, and the upgrade then
fails.\r\n\r\nThis PR makes the backfill operation here more
fail-safe.","sha":"b5abc4ec7e308815b0f338f4c836a9caf3ee48a3","branchLabelMapping":{"^v9.0.0$":"main","^v8.16.0$":"8.x","^v(\\d+).(\\d+).\\d+$":"$1.$2"}},"sourcePullRequest":{"labels":["release_note:skip","Team:Fleet","v9.0.0","backport:prev-major"],"title":"[UII]
Make constant keyword backfill
optional","number":192921,"url":"https://github.com/elastic/kibana/pull/192921","mergeCommit":{"message":"[UII]
Make constant keyword backfill optional (#192921)\n\n##
Summary\r\n\r\nFollow up to #188145. In some edge
cases\r\n(elastic/sdh-beats#5156), users could
override\r\nthe index template used by integration data streams. It is
possible to\r\ncreate an index template without mappings, this
causes\r\n`fillConstantKeywordValues` to receive an undefined object
when\r\nupgrading the integration, and the upgrade then
fails.\r\n\r\nThis PR makes the backfill operation here more
fail-safe.","sha":"b5abc4ec7e308815b0f338f4c836a9caf3ee48a3"}},"sourceBranch":"main","suggestedTargetBranches":[],"targetPullRequestStates":[{"branch":"main","label":"v9.0.0","branchLabelMappingKey":"^v9.0.0$","isSourceBranch":true,"state":"MERGED","url":"https://github.com/elastic/kibana/pull/192921","number":192921,"mergeCommit":{"message":"[UII]
Make constant keyword backfill optional (#192921)\n\n##
Summary\r\n\r\nFollow up to #188145. In some edge
cases\r\n(elastic/sdh-beats#5156), users could
override\r\nthe index template used by integration data streams. It is
possible to\r\ncreate an index template without mappings, this
causes\r\n`fillConstantKeywordValues` to receive an undefined object
when\r\nupgrading the integration, and the upgrade then
fails.\r\n\r\nThis PR makes the backfill operation here more
fail-safe.","sha":"b5abc4ec7e308815b0f338f4c836a9caf3ee48a3"}}]}]
BACKPORT-->

Co-authored-by: Jen Huang <[email protected]>

x-pack/plugins/fleet/server/services/epm/elasticsearch/template/template.test.ts

@@ -1867,6 +1867,110 @@ describe('EPM template', () => {
         },
       });
     });
+
+    it('should fill constant keywords from previous mappings', async () => {
+      const esClient = elasticsearchServiceMock.createElasticsearchClient();
+      esClient.indices.getDataStream.mockResponse({
+        data_streams: [{ name: 'test-constant.keyword-default' }],
+      } as any);
+      esClient.indices.get.mockResponse({
+        'test-constant.keyword-default': {
+          mappings: {
+            properties: {
+              some_keyword_field: {
+                type: 'constant_keyword',
+              },
+            },
+          },
+        },
+      } as any);
+      esClient.indices.simulateTemplate.mockResponse({
+        template: {
+          settings: { index: {} },
+          mappings: {
+            properties: {
+              some_keyword_field: {
+                type: 'constant_keyword',
+                value: 'some_value',
+              },
+            },
+          },
+        },
+      } as any);
+      const logger = loggerMock.create();
+      await updateCurrentWriteIndices(esClient, logger, [
+        {
+          templateName: 'test',
+          indexTemplate: {
+            index_patterns: ['test-constant.keyword-*'],
+            template: {
+              template: {
+                settings: { index: {} },
+                mappings: { properties: {} },
+              },
+            },
+          } as any,
+        },
+      ]);
+      const putMappingsCalls = esClient.indices.putMapping.mock.calls;
+      expect(putMappingsCalls).toHaveLength(1);
+      expect(putMappingsCalls[0][0]).toEqual({
+        index: 'test-constant.keyword-default',
+        body: {
+          properties: {
+            some_keyword_field: {
+              type: 'constant_keyword',
+              value: 'some_value',
+            },
+          },
+        },
+        write_index_only: true,
+      });
+    });
+
+    it('should not error when previous mappings are not found', async () => {
+      const esClient = elasticsearchServiceMock.createElasticsearchClient();
+      esClient.indices.getDataStream.mockResponse({
+        data_streams: [{ name: 'test-constant.keyword-default' }],
+      } as any);
+      esClient.indices.get.mockResponse({
+        'test-constant.keyword-default': {
+          mappings: {
+            properties: {
+              some_keyword_field: {
+                type: 'constant_keyword',
+              },
+            },
+          },
+        },
+      } as any);
+      esClient.indices.simulateTemplate.mockResponse({
+        template: {},
+      } as any);
+      const logger = loggerMock.create();
+      await updateCurrentWriteIndices(esClient, logger, [
+        {
+          templateName: 'test',
+          indexTemplate: {
+            index_patterns: ['test-constant.keyword-*'],
+            template: {
+              template: {
+                settings: { index: {} },
+                mappings: { properties: {} },
+              },
+            },
+          } as any,
+        },
+      ]);
+      const putMappingsCalls = esClient.indices.putMapping.mock.calls;
+      expect(putMappingsCalls).toHaveLength(1);
+      expect(putMappingsCalls[0][0]).toEqual({
+        index: 'test-constant.keyword-default',
+        body: {},
+        write_index_only: true,
+      });
+    });
+
     it('should rollover on expected error', async () => {
       const esClient = elasticsearchServiceMock.createElasticsearchClient();
       esClient.indices.getDataStream.mockResponse({

x-pack/plugins/fleet/server/services/epm/elasticsearch/template/template.ts

@@ -1027,10 +1027,16 @@ const updateExistingDataStream = async ({
     );
 
     settings = simulateResult.template.settings;
-    mappings = fillConstantKeywordValues(
-      currentBackingIndexConfig?.mappings || {},
-      simulateResult.template.mappings
-    );
+
+    try {
+      mappings = fillConstantKeywordValues(
+        currentBackingIndexConfig?.mappings || {},
+        simulateResult.template.mappings || {}
+      );
+    } catch (err) {
+      logger.error(`Error filling constant keyword values: ${err}`);
+      mappings = simulateResult.template.mappings;
+    }
 
     lifecycle = simulateResult.template.lifecycle;