The cutting edge of the Web just bled a little.

On Friday night, lightning in Virginia took out part of Amazon’s cloud computing service, called Amazon Web Services, which hundreds of companies use for data storage and computation. Well-known sites like Netflix , Pinterest and Instagram were not accessible for hours. There was little information for customers about what had happened, or even whether user data was safe.

The interruption underlined how businesses and consumers are increasingly exposed to unforeseen risks and wrenching disruptions as they increasingly embrace life in the cloud. It was also a big blow to what is probably the fastest-growing part of the media business, start-ups on the social Web that attract millions of users seemingly overnight.

Besides Internet-connected computers, tablets and smartphones, which people rely on daily, consumers and businesses are connected to the Web through everything from cars and appliances to utility monitors and surveillance cameras. How well the systems behind these are built, and how they handle unforeseen disruptions, will increasingly affect the larger economy.

Amazon has built a thriving business in cloud computing, with a range of customers including Intercontinental Hotels, Fox Entertainment, Unilever, Spotify, as well as 187 government agencies and hundreds of small start-ups looking for the cheapest possible computing.

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