How do you implement a simple supervision tree?

A supervision tree starts with a top-level supervisor whose init/1 callback declares a restart strategy and a child specification list; each child can itself be a worker or another supervisor, nesting arbitrarily deep.

init([]) ->
    SupFlags = #{strategy => one_for_one, intensity => 5, period => 10},
    Children = [
        #{id => cache_worker,
          start => {cache_worker, start_link, []},
          restart => permanent,
          type => worker}
    ],
    {ok, {SupFlags, Children}}.

Starting the top supervisor with supervisor:start_link/3 automatically starts every declared child in order. If cache_worker crashes, the one_for_one strategy restarts just that child (up to 5 times per 10 seconds, per intensity/period); exceeding that threshold escalates the crash to the supervisor's own parent.

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