How does AWS ensure that spikes from Amazon.com (e.g. during Black Friday) do not affect performance for other customers?

AWS employs a number of measures to ensure that spikes in traffic from Amazon.com do not affect the performance of other customers. Some of these measures include using separate infrastructure for Amazon.com, overprovisioning capacity to handle peak traffic, and implementing advanced traffic management technologies such as load balancing and auto scaling. Additionally, AWS has a number of services and features, such as Amazon Elasticache and Amazon DynamoDB, that are specifically designed to handle high-traffic workloads and ensure consistent performance for all customers.

In more detail, AWS infrastructure overall is designed with 30 regions and 96 availability zones globally (at time of writing), each AZ isolating the cloud workloads with independent power, cooling, and networking. Should an entire AZ fail, depending on how customers' environments are set up (each env can have entirely different architecture), it’s possible to failover workloads to one of the other zones in the same region, a capability known as “Multi-AZ” redundancy. Within each AZ, cloud workloads are isolated to specific EC2 instances, servers, ELBs, and more, ensuring that Amazon.com traffic scaling does not impact other customers.