public int getInstanceCount() {
        return this.serverGroupList.stream()
                .map(ServerGroup::getInstanceList)
                .mapToInt(List::size)
                .sum();
    }
@author emeroad
@author netspider
@author minwoo.jung
@author HyunGil Jeong
web/src/main/java/com/navercorp/pinpoint/web/applicationmap/nodes/ServerGroupList.java