Error 19407 means the lease between an availability group and the Windows Server Failover Cluster has expired, and the group goes to Resolving. Here is what each ERRORLOG line says and what to look at first.
SQL SERVER – Availability Group Missing or Deleted Automatically?
Investigate an availability group missing from SSMS by comparing SQL metadata, replica state and cluster logs before choosing a recovery procedure.
SQL SERVER – FIX: Error 19456: None of the IP Addresses Configured for the Availability Group Listener can be Hosted by the Server
Deploying a hybrid AlwaysOn availability group across on-premises and Azure, adding a replica failed with error 19456. Here is what fixed it.
Do You Need an Availability Group? Matching RPO and RTO to a Feature
Match RPO and RTO to backups, log shipping, failover clusters, or availability groups, then test the full service recovery path.
Writing a Disaster Recovery Runbook: RPO, RTO and a Restore Test
Build a disaster recovery runbook around agreed RPO and RTO, usable backup chains, instance dependencies, clear roles, and restore tests.
Resolving State: Why an AlwaysOn Availability Group Gets Stuck
Resolving state is the intermediate state of an AlwaysOn availability group during a role change. If the transition fails, the group stays there and the database is not accessible. Here is what the ERRORLOG showed in one case.
Bring SQL Cluster Resource Online When It Sits in Online Pending
A client could start a SQL Server instance from services.msc but could not bring SQL cluster resource online in Failover Cluster Manager. Here is how I checked the connection and found the cause: a TCP alias with an old port.