Auto Scaling
A service that automatically adjusts the number of EC2 instances to match demand.
AWS Auto Scaling monitors demand and automatically adjusts the number of EC2 instances — or units of other scalable resources — to maintain steady performance without over-provisioning. It works through scaling policies: target tracking keeps a chosen metric (such as average CPU utilization) at a set target, while step scaling responds to CloudWatch alarms in incremental steps. A common exam confusion is treating Auto Scaling and Elastic Load Balancing as interchangeable. They are complementary, not equivalent: Auto Scaling controls the fleet size, while ELB distributes incoming requests across the running instances. Both are needed for an elastic, highly available architecture.
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