You can test all you like on a staging environment, but until you have tested your prod you can never be 100% sure. That said, I wasn't thinking of DOSing your

You can test all you like on a staging environment, but until you have tested your prod you can never be 100% sure. That said, I wasn't thinking of DOSing yourself and bringing your servers down. But I could definitely see a use for a service where it gradually increases the load till response times hit some threshold.