How many licenses do I need to purchase for a SQL Server running in a cluster configuration?

How many licenses do I need to purchase for a SQL Server running in a cluster configuration?

It depends. For a 2-node cluster, running in the Active/Active configuration, two (2) production licenses are required. If your cluster node is running in the Active/Passive configuration, only one (1) license is required.

See the section called "Disaster Recovery, Cluster and Passive Nodes" in the Licensing documentation page for more information.