SQL Monitor is licensed per Windows server (either physical or virtual).
If running a Windows cluster, every node participating in the cluster requires a license. This includes passive nodes: these are automatically detected, and it is not possible to monitor only part of a cluster.
SQL Monitor licensing does not check the number of SQL Instances installed on an individual server.
Licensing for Azure SQL Databases
The licensing model for Azure SQL Databases requires one full SQL Monitor license allocation per five Azure SQL databases.
Licensing for Azure Managed Instances
Azure Managed Instances require one full SQL Monitor license per Managed Instance.
SQL Toolbelt Licensing
Whilst SQL Toolbelts are licensed per user, SQL Monitor (as part of the Toolbelt) is still licensed per server (physical or virtual).
Example: You have a 30 user SQL Toolbelt licence - this entitles you to 30 SQL Monitor licenses.
Example 1: You have 3 standalone Windows Servers, each with 15 SQL Server instances installed. You require 3 SQL Monitor licenses.
Example 2: You have 12 standalone Windows Servers, each with a single SQL Server instance installed. You require 12 SQL Monitor licenses.
Example 3: You have a 6 node Windows Cluster, with 5 SQL Server instances installed on each node. You require 6 SQL Monitor licenses.
Example 4: You have 5 standalone Windows Servers, each with 5 SQL Server instances installed, and 12 Azure SQL Databases. You require 8 SQL Monitor licenses.
Example 5: You have 5 standalone Windows Servers, and 3 Azure Managed Instances. You require 8 SQL Monitor licenses.