Exercise 2: ConfigMap as Env Var vs. Mounted Volume — What Happens on a Change — Possible Solution
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ENVIRONMENT VARIABLE consumption: per the chapter, env vars are
"injected at container startup" and "a running pod does NOT pick up a
later change, since env vars are only read once." This means if a
ConfigMap's value is updated AFTER a pod is already running, that
already-running pod continues operating with the OLD value it was
given at startup -- indefinitely, until the pod is deleted and
recreated (for example, via a new rollout, per Chapter 5's own
material), at which point the freshly-created pod would read the
NEW, current value at its own startup.

MOUNTED VOLUME consumption: per the chapter, this "updates
automatically (with some delay) if the underlying ConfigMap/Secret
changes, without restarting the pod." This means an application
reading its configuration from the FILE at the mount path can, if
designed to periodically re-read that file, pick up the updated value
WITHOUT the pod needing to be deleted or recreated at all -- the
update propagates to the mounted file directly while the pod continues
running.

The practical consequence: if an application needs to respond to
configuration changes live, without a restart, it needs to consume
that configuration via a MOUNTED VOLUME and actively re-read the file
periodically (env vars fundamentally cannot support this, since
they're fixed at process startup by the operating system itself, not
something Kubernetes can "push" an update into after the fact). If a
restart-on-change is acceptable, or even desired as part of a
deliberate redeploy process, env vars are simpler and fine to use.

WHY THIS WORKS AS AN ANSWER
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This directly contrasts the chapter's own two stated behaviors --
env vars fixed at startup vs. volume mounts updating live -- and
explains the underlying REASON for the difference (env vars are an
OS-level, startup-time mechanism; file contents can simply be
overwritten on disk while a process keeps running), rather than just
restating which one updates and which doesn't.