Thank you for posting your question. I understand that a Classic Load Balancer is, well, “classic” in the sense that it supports the legacy applications for EC2-Classic. It is also important to note that Classic Load Balancers are also suitable if your application is using custom security policies or protocols that are not supported by an Application Load Balancer (such as TCP). I actually still saw a bunch of Classic Load Balancer questions in the official SA Pro exam, which is why we still have this in our practice tests.
In this scenario, the legacy application requires a TCP connection. This can be fulfilled by using a Network Load Balancer (NLB) or a Classic Load Balancer. Again, the Application Load Balancer (ALB) doesn’t support TCP. The option that uses NLB has an incorrect port/protocol configuration, which only leaves us with CLB:
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Jon Bonso @ Tutorials Dojo