@Override
                public void onResponse(BulkResponse bulkItemResponses) {
                    if (bulkItemResponses.hasFailures()) {
                        LOGGER.warn("Errors were reported when submitting bulk metrics into Elasticsearch. "
                                            + "This may have resulted in a loss of data: {0}", bulkItemResponses.buildFailureMessage());
                    }
                }
Process the next item in the queue.
gateway/engine/es/src/main/java/io/apiman/gateway/engine/es/EsMetrics.java