Breaky provides a way to supervise and manage modules and processes depending on external resources. For these kind of processes standard OTP supervisors will not work. The problem is that if something fails, the supervisor can't return the state of an external process into a known good state by restarting. The supervisor has no control over it. When that happens too often, the supervisor will fail too, and if a supervisor is restarted often enough it can take down the whole system down.

Photo by leafbug

Breaky acts as a automatic circuit breaker "middleman" for these kind of processes. The process are started and managed in a normal OTP supervision tree. Restarts are managed by a circuit breaker FSM. When the FSM detects too many failures it will try to re-establish the service, but when a certaint threshold of restarts has been reached the restarts will be done in a slower rate and calls or casts to the failing process will result in off to notify that the circuit breaker is off and the process is not available. This will prevent the fault from cascading through the system.

Example:

    %% Start the circuit breaker for the database. It is an external resource.
    Args = [{user, "me"}, {password, "1234"}],
    {ok, _Pid} = breaky:start_circuit_breaker(db, {database, start_link, Args}),
 
    ...
    
    case breaky:call(db, "select * from my_table;") of
        off ->
            error_logger:error_msg("database unavailable"); 
            {error, db_unavailable};
        {ok, Result} ->
            Result
    end,
    ...