private void throwNoHostAvailableException() {
            final Throwable rootCause = ExceptionUtils.getRootCause(initializationFailure);
            // allow the certain exceptions to propagate as a cause
            if (rootCause instanceof SSLException || rootCause instanceof ConnectException) {
                throw new NoHostAvailableException(initializationFailure);
            } else {
                throw new NoHostAvailableException();
            }
        }
Initializes the connection pools on all hosts.
gremlin-driver/src/main/java/org/apache/tinkerpop/gremlin/driver/Client.java