VNet1 (10 web-server VMs) is peered with VNet2 (5 database-server VMs). You must enforce: database servers accept connections only from the web servers; web servers initiate connections only to the database servers; all NSGs are associated only with subnets; and use application security groups (ASGs) to implement the controls. What is the minimum number of application security groups required?

The minimum number of ASGs required is two. One ASG, let's call it ASG-Web, will contain all 10 web server VMs. Another ASG, ASG-DB, will contain all 5 database server VMs. You then create Network Security Group (NSG) rules that reference these ASGs. For example, an inbound rule on the database subnet's NSG would allow traffic from ASG-Web to ASG-DB on the database port. An outbound rule on the web server subnet's NSG would allow traffic from ASG-Web to ASG-DB on the database port. This setup ensures that only web servers can connect to database servers, and web servers only initiate connections to database servers, meeting all requirements efficiently. Using one ASG would not allow for distinct grouping of web and database servers, and four or eight would be excessive and unnecessary for this scenario.