public void add(final String instanceId) {
        final ScheduledFuture<?> task = this.scheduler.scheduleAtFixedRate(
                new ConsulHeartbeatTask(instanceId), ttl, ttl, TimeUnit.SECONDS);
        final ScheduledFuture<?> previousTask = this.serviceHeartbeats.put(instanceId, task);
        if (Objects.nonNull(previousTask)) {
            previousTask.cancel(true);
        }
    }
Add a service to the checks loop.
@param instanceId instance id
shenyu-registry/shenyu-registry-consul/src/main/java/org/apache/shenyu/registry/consul/TtlScheduler.java