protected void writeErrorResponseOnOverload(Request request, ResponseHandler responseHandler) {
        Response response = new Response(Response.Status.SERVICE_UNAVAILABLE);
        if (getRequestType().isPresent() && response.getRequestType() == null)
            response.setRequestType(getRequestType().get());
        ResponseDispatch.newInstance(response).dispatch(responseHandler);
    }
Invoked to write an error response when the worker pool is overloaded.
A subclass may override this method to define a custom response.
container-core/src/main/java/com/yahoo/container/jdisc/ThreadedRequestHandler.java