public SELF retryIntervalMillis(long retryIntervalMillis) {
        checkArgument(retryIntervalMillis > 0,
                      "retryIntervalMillis: %s (expected: > 0)", retryIntervalMillis);
        return retryBackoff(Backoff.fixed(retryIntervalMillis).withJitter(0.2));
    }
Sets the interval between health check requests in milliseconds. Must be positive.
core/src/main/java/com/linecorp/armeria/client/endpoint/healthcheck/AbstractHealthCheckedEndpointGroupBuilder.java