Multi-instance SQL with clusters

Can I create multiple default instances of SQL server on the same Windows server?

If, like me, you thought that due to the way that a SQL failover cluster has multiple IP addresses and host names, that you could make them all default instances, then you are mistaken. I was in the position where I had designed a SQL cluster to provide availability for many small databases that all needed to be in their own instance for security and audit requirements. Each database was small, so it did not justify creating a new SQL cluster for each database (in excess of $100,000 in hardware and licensing). I made the massive mistake of thinking that because they would all be installed in a different cluster resource group with it’s own IP address and installation of SQL, that this would mean that we could use port 1433 for each instance, and that we could use the default instance name (MSSQLSERVER).

However, due to the fact that you are installing an instance of SQL alongside an existing instance, you need to change the instance name to a named instance for each separate SQL installation. What’s more is that you need to go into SQL Configuration Manager and change (or find out) the port that is being used – because only one can use port 1433, even though they all have different IP addresses.