Swallows errors on ml lookups that we know might fail (elastic#25783) (…

…elastic#25844)

* Swallows errors on ml lookups that we know can fail

* Adjusts when we swallow ml lookup errors, fixes async test

x-pack/plugins/apm/server/lib/transactions/charts/get_avg_response_time_anomalies/__test__/get_anomaly_aggs.test.ts

@@ -0,0 +1,27 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License;
+ * you may not use this file except in compliance with the Elastic License.
+ */
+
+// @ts-ignore
+import { getAnomalyAggs } from '../get_anomaly_aggs';
+
+test('getAnomalyAggs should swallow HTTP errors', () => {
+  const httpError = new Error('anomaly lookup failed') as any;
+  httpError.statusCode = 418;
+  const failClient = jest.fn(() => Promise.reject(httpError));
+
+  return expect(getAnomalyAggs({ client: failClient })).resolves.toEqual(null);
+});
+
+test('getAnomalyAggs should throw other errors', () => {
+  const otherError = new Error('anomaly lookup ASPLODED') as any;
+  const failClient = jest.fn(() => Promise.reject(otherError));
+
+  return expect(
+    getAnomalyAggs({
+      client: failClient
+    })
+  ).rejects.toThrow(otherError);
+});

x-pack/plugins/apm/server/lib/transactions/charts/get_avg_response_time_anomalies/get_anomaly_aggs.js

@@ -62,10 +62,13 @@ export async function getAnomalyAggs({
   try {
     const resp = await client('search', params);
     return resp.aggregations;
-  } catch (e) {
-    if (e.statusCode === 404) {
+  } catch (err) {
+    if ('statusCode' in err) {
+      // swallow HTTP errors because there are lots of reasons
+      // the ml index lookup may fail, and we're ok with that
       return null;
     }
-    throw e;
+
+    throw err;
   }
 }

x-pack/plugins/apm/server/lib/transactions/charts/get_avg_response_time_anomalies/get_avg_response_time_anomalies.js

@@ -34,7 +34,7 @@ export async function getAvgResponseTimeAnomalies({
 
   if (!aggs) {
     return {
-      message: 'ml index does not exist'
+      message: 'Error reading machine learning index'
     };
   }