Amazon.com suffered a fresh round of outages on Monday amid speculation that it was under a denial of service attack.
Disruptions hit Amazon's US and UK sites Monday morning California time and lasted for about an hour, according to Keynote Systems, which monitors website performance. People who tried to visit the sites received a message reading: "Http/1.1 Service Unavailable." Amazon's US website experienced similar difficulties that lasted more than two hours on Friday.
Friday's outage coincided with a sustained attack on the Internet Movie Database, a popular site owned by Amazon that uses Amazon IP addresses. At the same time that Amazon's site became unavailable, a single attacker perpetrated a "layer 7" attack on IMDB. It flooded the site with so many requests for images that bandwidth and computing resources weren't able to accommodate legitimate users.
The average rate of the denial-of-service attack was about 3 Mbits/sec, according to this post from a researcher at Narus, which provides real-time traffic intelligence to large network operators.
What's more, shortly after Amazon technicians restored service after Friday's outage, several Register readers reported receiving a new error message that explained they were being blocked from Amazon.com because the requests were suspected to come from a bot or automatic script. Eventually, the problem was corrected.
Taken together, the IMDB attack and the false positives may indicate Amazon was hit by some sort of automatic script that contributed to the outage.
"It is definitely possible that they were undergoing an attack that our probes can't see and they tried to control it by dropping traffic," said Supranamaya Ranjan, a senior member of Narus's technical staff.
In addition to the possibility that miscreants unleashed an attack designed to hobble Amazon's webservers, some people have speculated that the outage was inadvertently caused by bots programmed to scoop up the Metal Gear Solid 4 bundle, an 80-GB pack for the PlayStation3, which went on sale on Amazon on Friday.
Whatever the cause, the outage comes as a pox on the house of Amazon. In addition to being the world's biggest online retailer, it's also trying to convince smaller companies to outsource their mission-critical storage, server and database operations to its Amazon Web Services.
An Amazon spokeswoman declined to discuss the cause of the outages. ®