Exercise 2: Init Container vs. Sidecar — The Timing Difference — Possible Solution
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The core difference, per the chapter: TIMING relative to the main
container.

INIT CONTAINER: runs to COMPLETION BEFORE the main container(s) even
START. It performs some setup or prerequisite task -- for example,
waiting for a dependency to become available, or preparing some data
the main container needs -- and then EXITS. Only once the init
container has finished successfully does Kubernetes start the pod's
main container(s) at all. An init container is never running AT THE
SAME TIME as the main container -- its entire job happens first, then
it's done.

SIDECAR: runs ALONGSIDE the main container, for the SAME DURATION.
Both start around the same time (or the sidecar may start once the
main container is ready) and both continue running together for as
long as the pod exists. A sidecar doesn't complete and exit before the
main container starts -- it's actively doing its own ongoing job (like
continuously shipping logs, per Exercise 1's example) throughout the
pod's entire running lifetime, in parallel with the main container.

Put simply: an init container's relationship to the main container is
SEQUENTIAL (finish, then the main container starts) -- a sidecar's
relationship is CONCURRENT (both run together, continuously, for the
whole life of the pod).

WHY THIS WORKS AS AN ANSWER
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This directly extracts the chapter's own distinguishing detail --
"runs to completion before the main containers start" for init
containers vs. "running alongside the main container" for sidecars --
and reframes it explicitly in terms of sequential-vs-concurrent
timing, which is the precise dimension the exercise asks about.