public UpdatableLoadBalancer<T> build() {
        validate();

        EventExecutor executor = executor();
        if (executor == null) {
            executor = CommonPools.workerGroup().next();
        }

        return new RampingUpLoadBalancer<>(candidates, weightFunction, rampingUpIntervalMillis(), totalSteps(),
                                           rampingUpTaskWindowMillis(), weightTransition(), timestampFunction(),
                                           ticker(),
                                           executor);
    }
Returns a newly-created weight ramping up {@link LoadBalancer} which ramps the weight of
newly added candidates. The candidate is selected using weighted random distribution.
core/src/main/java/com/linecorp/armeria/common/loadbalancer/RampingUpLoadBalancerBuilder.java