public SELF ticker(Ticker ticker) {
        requireNonNull(ticker, "ticker");
        this.ticker = ticker;
        return self();
    }
Sets the {@link Ticker} to use to measure time. {@link Ticker#systemTicker()} is used by default.
core/src/main/java/com/linecorp/armeria/common/loadbalancer/AbstractRampingUpLoadBalancerBuilder.java