I made a similar post about this for SharePoint 2010, but I wanted to update it (and make it more clear) for 2013.
Using a SQL Server alias, you’ll be able to change the database server in your SharePoint farm behind the scenes, without anyone in your SharePoint universe even knowing you’ve made a change. In addition, setting an alias should really be a best practice for most new farm builds. This technique is useful when moving or virtualising your database server, setting up a test environment, or especially when migrating from SQL Server 2005 / 2008 / 2008 R2 to SQL Server 2012 / 2014.
Repeat the following steps for all your SharePoint Frontend and Application Servers.
Important: Only do this on the SharePoint Servers. Don’t do this on the SQL Server!
The steps we’re going to run include the following:
1. Setup the alias using 32-bit config tool.
2. Setup the (same) alias using 64-bit config tool.
1. Run the 32-bit SQL tool. Run the following application, “C:\windows\system32\cliconfg.exe”
Select the tab “Alias” and click the button “Add”.
Next (as seen in the graphic below), (1) Select “TCP/IP” and define your alias (2). Next, fill in the original server name (3) of your database server and unselect the “Dynamically determine port” checkbox (4) – finally, define the port (5). After that click “OK”.
Note 1: If you know the port (typically 1433), you will need to uncheck the “Dynamically determine port” checkbox, and set the fixed value.
Note 2: If your new (or old) server is using an instance, be sure to include that, for example, something like itgrooveSQLServer\INSTANCENAME (ex. itgrooveSQLServer\SharePoint2013)
Note 3: If you have an existing SQL server without an Alias and are migrating that to a new machine and setting up an alias, the “Server Alias” value should be the name of the existing SQL server (2), and the Server name (3) should be the name of your new SQL server.
Now you have defined your SQL alias name. Click “OK”.
Note: It’s recommended that you should setup an alias for the server name itself, as well as it’s fully qualified name – for example, setup an alias for “itgrooveSQLServer”, as well as “itgrooveSQLServer.domain.com”.
2. Run the 64-bit SQL tool. Run the following application, “C:\windows\syswow64\cliconfg.exe”
Using the 64bit tool, repeat all the same steps you did above.
After you’ve completed steps (1) and (2) on each SharePoint Server, you can either create your new farm or restart your existing farm, and it should be working again with your new alias.
Original Source: http://splog.cairo.ag/2011/02/22/using-sql-server-alias-names-with-sharepoint-server-2010/ – Many thanks!