AWS Certified Advanced Networking - Specialty Exam Guide

Controlling access with the OS firewall

To fully control access to instances, we need to make sure that we are also appropriately configuring the operating system firewall. The initial benefit of the operating system firewall is that it protects our instance from any possible misconfiguration of the security groups while also allowing us another level of traffic logging at the perimeter of the operating system. The operating system firewall might also be configured differently than the security group in certain cases.

An example of this is when an application requires awareness and needs to maintain contact with its peers. This could be because the cluster needs to maintain a certain state that's distributed across the instances or some data ...