public SELF retryInterval(Duration retryInterval) {
        requireNonNull(retryInterval, "retryInterval");
        checkArgument(!retryInterval.isNegative() && !retryInterval.isZero(),
                      "retryInterval: %s (expected: > 0)", retryInterval);
        return retryIntervalMillis(retryInterval.toMillis());
    }
Sets the interval between health check requests. Must be positive.
core/src/main/java/com/linecorp/armeria/client/endpoint/healthcheck/AbstractHealthCheckedEndpointGroupBuilder.java