Barrel Log Event Handler

barrel_log_event.erl

-module(barrel_log_event).
-behaviour(gen_server).

% public API
-export([start_link/0, stop/0]).

-export([init/1, handle_call/3, handle_cast/2, handle_info/2,
         terminate/2, code_change/3]).

start_link() ->
    gen_server:start_link({local, barrel_log_event}, barrel_log_event, [], []).

stop() ->
    couch_event_sup:stop(barrel_log_event).

init(X) ->
    lager_handler_watcher:start(lager_event, barrel_log_event_handler, []),
    {ok, X}.

handle_call(X, Y, Z) ->
    {ok, ok, Z}.

handle_cast(X, Y) ->
    {noreply, Y}.

handle_info(X, Y) ->
    {ok, Y}.

code_change(X, Y, Z) ->
    {ok, Y}.

terminate(X, Y) ->
    ok.

barrel_log_event_handler.erl

-module(barrel_log_event_handler).
-behaviour(gen_event).
 
-export([init/1, handle_event/2, handle_call/2, handle_info/2, code_change/3,
terminate/2]).
 
init([]) ->
    {ok, []}.
 
handle_event({log, Log}, State) ->
    io:format("****** LOG --------------  ~p ~n", [Log]),
    {ok, State};

handle_event(_, State) ->
    {ok, State}.
 
handle_call(_, State) ->
    {ok, ok, State}.
 
handle_info(_, State) ->
    {ok, State}.
 
code_change(_OldVsn, State, _Extra) ->
    {ok, State}.
 
terminate(_Reason, _State) ->
    ok.

barrel_sup.erl

%%%-------------------------------------------------------------------
%% @doc barrel_core top level supervisor.
%% @end
%%%-------------------------------------------------------------------

-module('barrel_sup').

-behaviour(supervisor).

%% API
-export([start_link/0]).

%% Supervisor callbacks
-export([init/1]).

-define(SERVER, ?MODULE).

%%====================================================================
%% API functions
%%====================================================================

start_link() ->
    supervisor:start_link({local, ?SERVER}, ?MODULE, []).

%%====================================================================
%% Supervisor callbacks
%%====================================================================

%% Child :: {Id,StartFunc,Restart,Shutdown,Type,Modules}
init([]) ->

    UUIDs = {barrel_uuids,
             {barrel_uuids, start_link, []},
             permanent, brutal_kill, worker, [barrel_uuids]},

    Log = {barrel_log,
           {barrel_log, start_link, []},
           permanent, brutal_kill, worker, [barrel_log]},

    LogEvent = {barrel_log_event,
           {barrel_log_event, start_link, []},
           permanent, brutal_kill, worker, [barrel_log_event]},

    {ok, { {one_for_all, 0, 1}, [UUIDs, Log, LogEvent]} }.

%%====================================================================
%% Internal functions
%%====================================================================

do you need https://gist.github.com/sivsushruth/d6a4a9b2c8dc1c2d1c3c97a97d986943#file-barrel_sup-erl-L40-L42 ?

Anyway the idea sounds good according the infos you gave on slack. Go ahead, I will review the PR :)