Amazon Web Services
Core Compute — EC2 & Auto Scaling
Rent virtual servers on demand and scale them horizontally behind a load balancer.
Amazon EC2 (Elastic Compute Cloud) provides resizable virtual machines called instances. You choose an instance family tuned for a workload — general purpose (M/T), compute-optimised (C), memory-optimised (R/X), or accelerated (G/P for GPUs) — and a size within it. Instances boot from an AMI (Amazon Machine Image) and run inside a VPC subnet in a chosen Availability Zone.
Renting cars from an agency instead of buying a fleet. You pick the model you need, take more during busy season and return them when quiet — and if one breaks down the agency swaps it for a working one automatically.
Key Concepts
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Real systems rarely run a single instance. An Auto Scaling Group keeps a fleet at a target size across multiple AZs, replacing unhealthy instances and adding or removing capacity based on metrics. An Application/Network Load Balancer spreads traffic across the fleet. Pricing models trade flexibility for cost: On-Demand for spiky/unknown load, Reserved Instances or Savings Plans for steady baseline, and Spot for interruptible batch work at up to ~90% discount.