It could be DNS. Azure has had an all-region failure due to a single DNS provider outage. It was possible that same DNS provider's outage was also causing problems for GCE and AWS at the same time.
That wouldn't be at the top of my list. We have "Volumes" for databases and they were inaccessible for like 6 hours. I don't think any DNS is involved in mounting these. But hey, there's always a lot of crap hidden behind the scenes :)