Update elastic engine to preserve pre-existing indices if indexer receives 0 documents

Signed-off-by: Eric Peterson <ericpeterson@spotify.com>

plugins/search-backend-module-elasticsearch/src/engines/ElasticSearchSearchEngine.ts

@@ -252,6 +252,7 @@ export class ElasticSearchSearchEngine implements SearchEngine {
 
   async getIndexer(type: string) {
     const alias = this.constructSearchAlias(type);
+    const indexerLogger = this.logger.child({ documentType: type });
 
     const indexer = new ElasticSearchSearchEngineIndexer({
       type,
@@ -259,13 +260,13 @@ export class ElasticSearchSearchEngine implements SearchEngine {
       indexSeparator: this.indexSeparator,
       alias,
       elasticSearchClientWrapper: this.elasticSearchClientWrapper,
-      logger: this.logger,
+      logger: indexerLogger,
       batchSize: this.batchSize,
     });
 
     // Attempt cleanup upon failure.
     indexer.on('error', async e => {
-      this.logger.error(`Failed to index documents for type ${type}`, e);
+      indexerLogger.error(`Failed to index documents for type ${type}`, e);
       let cleanupError: Error | undefined;
 
       // In some cases, a failure may have occurred before the indexer was able
@@ -296,11 +297,13 @@ export class ElasticSearchSearchEngine implements SearchEngine {
       });
 
       if (cleanupError) {
-        this.logger.error(
+        indexerLogger.error(
           `Unable to clean up elastic index ${indexer.indexName}: ${cleanupError}`,
         );
       } else {
-        this.logger.info(`Removed partial, failed index ${indexer.indexName}`);
+        indexerLogger.info(
+          `Removed partial, failed index ${indexer.indexName}`,
+        );
       }
     });
 

plugins/search-backend-module-elasticsearch/src/engines/ElasticSearchSearchEngineIndexer.test.ts

@@ -176,6 +176,26 @@ describe('ElasticSearchSearchEngineIndexer', () => {
     expect(deleteSpy).toHaveBeenCalled();
   });
 
+  it('handles when no documents are received', async () => {
+    await TestPipeline.fromIndexer(indexer).withDocuments([]).execute();
+
+    // Older indices should have been queried for.
+    expect(catSpy).toHaveBeenCalled();
+
+    // A new index should have been created.
+    const createdIndex = createSpy.mock.calls[0][0].path.slice(1);
+    expect(createdIndex).toContain('some-type-index__');
+
+    // No documents should have been sent
+    expect(bulkSpy).not.toHaveBeenCalled();
+
+    // Alias should not have been rotated.
+    expect(aliasesSpy).not.toHaveBeenCalled();
+
+    // Old index should not be cleaned up.
+    expect(deleteSpy).not.toHaveBeenCalled();
+  });
+
   it('handles bulk and batching during indexing', async () => {
     const documents = range(550).map(i => ({
       title: `Hello World ${i}`,

plugins/search-backend-module-elasticsearch/src/engines/ElasticSearchSearchEngineIndexer.ts

@@ -131,6 +131,24 @@ export class ElasticSearchSearchEngineIndexer extends BatchSearchEngineIndexer {
     // Wait for the bulk helper to finish processing.
     const result = await this.bulkResult;
 
+    // Warn that no documents were indexed, early return so that alias swapping
+    // does not occur, and clean up the empty index we just created.
+    if (this.processed === 0) {
+      this.logger.warn(
+        `Index for ${this.type} was not ${
+          this.removableIndices.length ? 'replaced' : 'created'
+        }: indexer received 0 documents`,
+      );
+      try {
+        await this.elasticSearchClientWrapper.deleteIndex({
+          index: this.indexName,
+        });
+      } catch (error) {
+        this.logger.error(`Unable to clean up elastic index: ${error}`);
+      }
+      return;
+    }
+
     // Rotate main alias upon completion. Apply permanent secondary alias so
     // stale indices can be referenced for deletion in case initial attempt
     // fails. Allow errors to bubble up so that we can clean up the created index.