final Map<String, Object> map = new LinkedHashMap<>();
        map.put("type", "heartbeat");
        map.put("instanceId", "test-instance");
        map.put("createdTime", 1000L);

        final String json = coordinatorHelper.toJson(map);
        assertNotNull(json);
        assertTrue(json.contains("\"type\":\"heartbeat\""));
        assertTrue(json.contains("\"instanceId\":\"test-instance\""));

                logger.warn("Failed to send heartbeat: status={}", response.getHttpStatusCode());
            }
        } catch (final Exception e) {
            logger.debug("Failed to send heartbeat.", e);
        }
    }

    /**
     * Removes the heartbeat document for this instance from OpenSearch.
     */
    protected void removeHeartbeat() {

#                                                Coordinator
#                                                     ------

# Interval (seconds) for polling heartbeats and events.
coordinator.poll.interval=60
# Time-to-live (ms) for instance heartbeat documents.
coordinator.heartbeat.ttl=180000
# Time-to-live (ms) for operation lock documents.
coordinator.operation.ttl=7200000
# Maximum number of retries for acquiring an operation lock.

     * @return The value of found property. (NotNull: if not found, exception but basically no way)
     */
    String getCoordinatorHeartbeatTtl();

    /**
     * Get the value for the key 'coordinator.heartbeat.ttl' as {@link Integer}. <br>
     * The value is, e.g. 180000 <br>
     * comment: Time-to-live (ms) for instance heartbeat documents.