Addition of new servers led to massive outage last week: AWS

New Delhi, Nov 29 : The addition of new servers to the network triggered the massive outage of Amazon Web Services (AWS) last week, affecting several websites and apps, the company has acknowledged.
AWS, which is the Cloud arm of e-commerce behemoth Amazon, said they were able to confirm a root cause which was not driven by memory pressure as earlier reported.
“Rather, the new capacity had caused all of the servers in the fleet to exceed the maximum number of threads allowed by an operating system configuration,” the company said in a technical blog post.
“As this limit was being exceeded, cache construction was failing to complete and front-end servers were ending up with useless shard-maps that left them unable to route requests to back-end clusters,” it added.
The capacity addition was being made to the front-end fleet of AWS.
Each server in the front-end fleet maintains a cache of information, including membership details and shard ownership for the back-end clusters, called a shard-map.