Add an encrypted database to an Always On availability group
This topic contains information about the using currently encrypted or recently decrypted databases with Always On availability groups in SQL Server 2017.
Limitations and Restrictions
If a database is encrypted or even contains a Database Encryption Key (DEK), you cannot use the New Availability Group Wizard or Add Database to Availability Group Wizard to add the database to an availability group. Even if an encrypted database has been decrypted, its log backups might contain encrypted data. In this case, full initial data synchronization could fail on the database. This is because the restore log operation might require the certificate that was used by the database encryption keys (DEKs), and that certificate might be unavailable.
To make a decrypted database eligible to add to an availability group using the wizard:
Create a log backup of the primary database.
Create a full database backup of the primary database.
Restore the database backup on the server instance that hosts the secondary replica.
Create a new log backup from primary database.
Restore this log backup on the secondary database.