Cloud computing is the on-demand delivery of IT resources over the internet with pay-as-you-go pricing, replacing the need to own and operate physical data centers. Major providers include AWS, Azure, and Google Cloud. The three main service models describe who manages what: in IaaS (Infrastructure as a Service), exemplified by Amazon EC2, the provider manages hardware while the customer manages the operating system, applications, and data; in PaaS (Platform as a Service), exemplified by Elastic Beanstalk, the provider manages the operating system and runtime while customers focus on code and data; and in SaaS (Software as a Service), exemplified by Gmail and Salesforce, the provider manages everything and users simply consume the application.
The AWS Shared Responsibility Model formalizes who secures what. AWS is responsible for security of the cloud, which covers hardware, networking, facilities, and managed services. The customer is responsible for security in the cloud, which covers data encryption, IAM policies, operating system patching, firewall rules, and application code. Misunderstanding this boundary is one of the most common sources of cloud security incidents.
AWS organizes its global infrastructure into Regions (such as us-east-1), each a separate geographic area containing multiple isolated data centers called Availability Zones. Each AZ has independent power, networking, and connectivity, and deploying across multiple AZs provides high availability and fault tolerance. EC2 Placement Groups refine this further: cluster placements pack instances close for low latency in HPC workloads, spread placements separate them across distinct hardware to limit correlated failures (up to seven per AZ), and partition placements spread instances across logical partitions for workloads like Hadoop and Kafka.
The AWS Well-Architected Framework describes six pillars for designing cloud workloads: Operational Excellence, Security, Reliability, Performance Efficiency, Cost Optimization, and Sustainability. The free AWS Well-Architected Tool and its domain-specific Lenses help teams review workloads against these pillars and track risks. Trusted Advisor analyzes accounts for Cost Optimization, Security, Fault Tolerance, Performance, and Service Limits, with full checks available on Business or Enterprise support. AWS Organizations centralizes management across multiple accounts via Organizational Units and Service Control Policies (SCPs), which act as permission boundaries rather than grants. AWS Control Tower automates the setup of secure multi-account environments with preventive and detective guardrails, while IAM Identity Center (formerly AWS SSO) replaces per-account IAM users for everyday human access across the organization. New accounts can explore services through the AWS Free Tier, which combines always-free monthly limits with twelve-month-free promotions and short trials, and can choose support tiers from Basic (free) through Developer and Business to Enterprise On-Ramp and Enterprise, which adds fifteen-minute response times and a designated Technical Account Manager.