REL 4. How does your system adapt to changes in demand?
A scalable system can provide elasticity to add and remove resources automatically so that they closely match the current demand at any given point in time.

Best practices:

 Automated scaling Use automatically scalable services, e.g., Amazon S3, Amazon CloudFront, Auto Scaling, Amazon DynamoDB, AWS Elastic Beanstalk, etc.
 Load Test Adopt a load testing methodology to measure if scaling activity will meet application requirements.