A web application firewall (WAF) is a security solution that monitors and filters the traffic between a web application and the Internet. A WAF can help improve the site security by blocking malicious requests, preventing SQL injection attacks, mitigating cross-site scripting (XSS) attacks, and enforcing security policies. A WAF can be deployed as a cloud service or as a device in front of the load balancer. A WAF is more suitable than an API gateway, an IPS/IDS, or a reverse proxy for the website architecture described in the question. Reference: [CompTIA Cloud+ CV0-003 Certification Study Guide], Chapter 9, Objective 9.1: Given a scenario, apply security controls and techniques.