概念：https://blog.csdn.net/Hehuyi_In/article/details/103529698
实践：https://blog.csdn.net/Hehuyi_In/article/details/104868576
官网：https://docs.microsoft.com/zh-cn/sql/database-engine/availability-groups/windows/distributed-availability-groups?view=sql-server-2016#monitor-distributed-availability-group-health
