This document provides an introduction to cloud systems architecture. It discusses key concepts like public cloud providers (AWS, Azure, GCP), the "as a service" model (IaaS, PaaS, SaaS, FaaS), typical system architecture layers (compute, storage, databases, messaging, analytics), and a demo of setting up a scalable blog on AWS using EC2, auto scaling, and serverless computing. The future of cloud systems is moving toward serverless architectures that abstract away infrastructure management.