private void sleepBeforeRetry(int tryNum) {
        try {
            int sleep = (tryNum + 1) * 100;
            logger.debug("Sleeping for " + sleep + "ms ...");
            Thread.sleep(sleep); // making this seconds based is too slow
            // i.e. 200ms, 400 ms, 800ms, 1600ms etc.
        } catch (InterruptedException ex) {
        }
    }
Prime servers asynchronously.

@param servers
@param listener
ribbon-loadbalancer/src/main/java/com/netflix/client/PrimeConnections.java