This is one of those jobs that looks so simple on the outside, but can lead you down a massive rabbit hole if you're not too careful:
We're in the process of changing an instance of SharePoint from a true "Single Server" setup to having the databases on a separate SQL Server, and there's plenty of documentation about that, starting with: Move all databases
We'd also followed the recommendations in Harden SQL Server for SharePoint Environments but after we'd moved the Content Database to the new server and attached it in SQL, all attempts to "Add a content database" in Central Admin resulted in errors such as:
Cannot connect to database master at SQL server at SqlServer2. The database might not exist, or the current user does not have permission to connect to it.
Digging into the ULS logs we found the following Critical errors:
Unknown SQL Exception 53 occurred. Additional error information from SQL Server is included below. A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server)
It turns out that sometimes the SQL Configuration Manager needs a little bit of a helping hand, and you need start the Old School "SQL Server Client Network Utility" with the command (note the 8.3 format of the name):
On the Alias tab of this app, add the Aliases you added in the SQL Configuration Manager, and you should be good to go.
Filed under: Fixes, SharePoint