This is the way large web operations such as Google and Facebook manage Internet-scale data processing, although the Web players tend to take a do-it-yourself approach based on internally developed or open-source software.
If an act of nature, a specific supplier or some other uncontrollable act can make it impossible for you to fulfill a contract (and thus openyourself up to legal action) then you should be putting to ink that you are not liable for incomplete work due to these factors.