Amazon Web Services was the most reliable of the “big three” cloud services – AWS, Google Compute Engine and Microsoft Azure – according to two seperate studies by companies that analyze cloud outages.

CloudEndure, which offers public cloud migration assistance to enterprises, says AWS saw a 488 percent reliability improvement during 2014, with just 230 service interruptions throughout the year, and no major outages. That compares rather well with Microsoft Azure, which saw over 500 service interruptions and two major outages in the last year.

The analysis tallies with a report released earlier in the month by CloudHarmony, a company that analyzes cloud reliability risks and provides a much more in-depth look at the state of play than CloudEndure.

According to CloudHarmony, Amazon EC2 experienced ten outages across various regions over the last year, with the longest of these lasting nine minutes and the shortest lasting just 19 seconds. Google Compute Engine saw around 60 outages over the same period, lasting from ten seconds to 37 minutes. And sadly for Microsoft, its Azure Virtual Machines reportedly suffered over 100 outages, with the longest lasting a headache-inducing 12 hours.

The two firm’s analysis differs because CloudHarmony tracks region-wide outages, while CloudEndure reports service errors.

CloudHarmony says that Azure’s biggest outage occurred last August, when full service interruptions were reported across multiple regions. It also suffered a second major outage in November, when about twenty of its services went offline in “most of its availability zones”. As for the 12-hour outage, that occurred on November 5 but was localized to the asia-east zone.

The good news for both Microsoft and AWS is that error rates dropped consistently as the year progressed. The number of errors witnessed by Azure fell from 260 in the first quarter to around 200 in the fourth quarter. Meanwhile, AWS went from 127 errors in Q1 to just 26 in Q4, which suggests its fast becoming a very reliabile cloud platform indeed.

While cloud providers ability to maintain uptime is important, the main cause of most outages was due to human error, said Ofir Ehrlich, vice president of research and development at CloudEndure, in a blog post. For companies that rely on cloud services, the best way to protect against such outages is to setup resilient multi-region failover architecture regardless of which provider they’re using.

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