Explanation

Box 1: an internal load balancer
Azure Internal Load Balancer (ILB) provides network load balancing between virtual machines that reside inside a cloud service or a virtual network with a regional scope.
Box 2: an application gateway that uses the WAF tier
Azure Web Application Firewall (WAF) on Azure Application Gateway provides centralized protection of your web applications from common exploits and vulnerabilities. Web applications are increasingly targeted by malicious attacks that exploit commonly known vulnerabilities.
References:
https://docs.microsoft.com/en-us/azure/web-application-firewall/ag/ag-overview