Elasticity
- Definition
- Capacity automatically expands and contracts to match actual demand, in near real time.
- You stop guessing capacity and stop paying for idle headroom.
- How AWS delivers it
- AWS Auto Scaling for EC2, ECS, DynamoDB, and Aurora replicas.
- Serverless services scale inherently: AWS Lambda, AWS Fargate, Amazon S3, DynamoDB on-demand.
- load balancers distribute traffic across whatever capacity currently exists.
- Two directions
- Scale out / in (horizontal) — add or remove instances. The cloud-native default.
- Scale up / down (vertical) — resize an instance. Simpler but has a ceiling and usually needs a restart.
- Distinguish from neighbors
- Scalability — the ability to grow to handle more load; elasticity is doing it automatically and in both directions.
- High Availability — surviving failure, not tracking demand.
- Agility — speed of change for the business, not capacity matching.