Exercise 1: Why an Ingress Without a Controller Does Nothing — Possible Solution
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What's actually missing: an INGRESS CONTROLLER actually running in the
cluster.

Per the chapter, "an Ingress requires an Ingress controller actually
running in the cluster to read and implement those rules." The
Ingress RESOURCE itself is only a declarative description -- a set of
routing rules describing INTENT (which hostnames/paths should route to
which backend Services), written to etcd via the API server exactly
like any other Kubernetes object (Chapter 2's own architecture).

But per this chapter's own framing, an Ingress resource on its own is
purely a piece of DATA -- it has no behavior of its own, and nothing in
the core Kubernetes control plane (the API server, scheduler,
controller-manager, per Chapter 2) is going to interpret or ACT on
that specific data by actually watching network traffic and routing it
accordingly. That's specifically the job of an Ingress controller --
a separate piece of software (NGINX Ingress Controller, or a
cloud-provider-specific one, per the chapter) that has to be
deliberately installed into the cluster, whose job is to continuously
watch for Ingress resources and configure real routing (typically via
a proxy or load balancer it manages) to match what those Ingress
rules describe.

Without that controller running, creating an Ingress YAML is
equivalent to writing routing rules on a piece of paper that nobody
reads -- the rules exist as data, correctly stored in the cluster, but
nothing is actually watching for them or converting them into real,
functioning network behavior. No traffic would actually be routed
according to those rules; the Ingress resource would simply sit there,
inert.

WHY THIS WORKS AS AN ANSWER
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This distinguishes the Ingress resource (declarative data, no
inherent behavior) from the Ingress controller (the actual software
that reads and acts on that data) -- directly matching the chapter's
own tip-box, which specifically calls out this distinction as "a
genuinely common early confusion worth stating directly."