Exercise 1: "Connection Refused" on Port 8080 — What This Rules Out — Possible Solution
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What "connection refused" suggests is NOT the problem:

Per the chapter's own distinction, "connection refused" specifically
means something on the network path IS reachable and is actively
rejecting the connection -- as opposed to a "timeout," which would
mean packets are being silently dropped. This strongly suggests that a
silent-drop cause -- a security group or NACL BLOCKING the traffic
before it ever reaches the destination, or a missing route -- is
probably NOT the issue here, since a silent block would typically
produce a timeout (no response at all), not an active rejection.

Reasoning: if a security group or NACL were blocking port 8080
entirely, the connection attempt would simply hang with no response,
because the packet never reaches anything capable of actively
rejecting it in the first place. Getting an explicit "refused"
response means the packet DID make it through the network path far
enough to reach something that responded -- which rules out the most
common silent-drop causes as the primary explanation.

What should be checked instead:

Per the chapter's own explanation of "connection refused" -- "often
nothing is listening on that port, or an explicit reject rule exists"
-- the next step is checking whether the APPLICATION or service on the
destination host is actually running and listening on port 8080 at
all. This is exactly the final step of the chapter's full flowchart
("confirm the application itself is actually running and listening on
the expected port") -- except here, the specific error type (refused,
not timeout) is itself the clue that points directly at this step,
rather than needing to work through the earlier network-layer steps
first.

WHY THIS WORKS AS AN ANSWER
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This applies the chapter's own tip-box directly -- using the specific
failure type to skip straight to the most likely cause rather than
mechanically working through every checklist step in order. "Refused"
specifically points away from the network-layer blocking causes and
toward "is anything actually listening," which is exactly the
practical value the chapter's failure-type distinction is meant to
provide.