In day-to-day cloud operations, some incidents stand out not because of their complexity, but quite the opposite. They are those cases where, once you discover the root cause, you think: “this can’t be it”. This is one of them. ⸻ The scenario The EC2 instance was running, with a public IP and everything seemingly correct. Status: running Public IP available No visible alerts Even so, every attempt to access it resulted in a timeout. No clear error. No direct clue. ⸻ Where to look first In situations like this, before assuming something more complex, the first step is always to review the Security Group. More specifically: the inbound rules. ⸻ The problem When analyzing the Security Group, the situation was straightforward: No inbound rules configured. This means the instance was not accepting any external connections. No SSH, no HTTP, no any other port. This is expected behavior in AWS: everything is denied by default unless explicitly allowed.…