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YouTube, today around 7:30 PM CST, on all embeds and direct website calls began returning the error "Http/1.1 Service Unavailable," which soon thereafter was followed by a hard down in which even pings to the site returned "Request Timed Out."
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We gave the site 30 minutes to come back up, and checked official Google blogs for information about the downtime, and no word yet as of the the cause of the downtime. I would check Twitter to see what the buzz was on the topic, but as today is a day ending in "y," it is down as well.
We'll update you when we find out more, but at the moment, we're calling this one an 'epic fail.'