Cloud Concepts

Cloud computing is the on-demand delivery of compute, storage, networking, databases and higher-level services over the internet with pay-as-you-go pricing. Instead of buying servers and building a data center, you call an API (or click in a console) and a provider such as Amazon Web Services hands you capacity within minutes and bills for what you use. Virtualization — carving one physical host into many virtual machines — is a technology the cloud is built on, not the cloud itself: the cloud adds self-service provisioning, elastic scaling, metered billing and a provider that owns and operates the physical layer.

You interact with AWS in four ways, and the rest of the section uses all of them:

AWS summarises the benefits as six advantages. Each maps to concrete behaviour you will meet later:

Two ideas recur in those advantages. Scalability is the ability to add capacity: vertically ("scaling up", a bigger instance, with a ceiling and usually a restart) or horizontally ("scaling out", more instances behind a load balancer). Elasticity is the automated form of horizontal scaling, where capacity follows demand in both directions. High availability comes from redundancy across Availability Zones; it is measured in practice by the recovery time objective (RTO) and recovery point objective (RPO) you actually achieve in an incident.

Each step toward SaaS trades control for lower operational effort. The boundary is a continuum rather than four boxes: Elastic Beanstalk, Fargate and RDS each sit at a different point.

Multi-cloud is a related choice — using more than one public provider to reduce lock-in or reach different footprints — at the price of duplicated tooling and skills. The Bookshelf scenario used throughout this section is also implemented on Azure, so you can compare the two side by side.

Choosing a model comes down to compliance and data-residency requirements, latency to users or machinery, existing investment in hardware, and the skills available to operate each environment.

AWS describes security and compliance as a shared responsibility. AWS is responsible for security of the cloud: the facilities, the hardware, the network, and the software layer that virtualizes them. The customer is responsible for security in the cloud: everything they put on top and how they configure it. What moves with the service type is the line in between.

Data, identity and access configuration stay with the customer in every model, including SaaS. Misconfigured identity or a public bucket is a customer-side failure that no provider-side investment can offset; see Identity and Access and S3 Security and Static Hosting. AWS Artifact provides the compliance reports that document AWS’s side (see Governance, Security and Compliance).

Running your own data center is capital expenditure (CapEx): large upfront purchases, depreciated over years and sized for a peak that may not arrive. Cloud consumption is operating expenditure (OpEx): a variable cost that follows usage, with nothing to buy upfront and nothing to dispose of. AWS bills most services per second or hour of use, per gigabyte stored or per request, and a deleted resource stops accruing charges (apart from retained backups and snapshots, which are billed until removed).

Related cost concepts:

Current prices change, so this section never quotes them; use the dated official pricing pages and the Pricing Calculator. Cost drivers, budgets and support plans are in Cost Management and Support.

The Well-Architected Framework describes best practices for designing and operating workloads, organised into six pillars:

The free AWS Well-Architected Tool in the console lets you review a workload against these pillars by answering questions per pillar, and lenses add guidance for specific domains. The migration-oriented view is in Architecture, Migration, Hybrid and Disaster Recovery.

The AWS Cloud Adoption Framework (CAF) helps an organisation plan its move to the cloud and evolve a transformation roadmap. It groups guidance into six perspectives: Business, People and Governance address business capabilities; Platform, Security and Operations address technical ones. Typical work begins by assessing readiness per perspective, then prioritising the gaps in an action plan. Where Well-Architected reviews one workload, the CAF looks at the organisation. Multi-account structure and guardrails, one outcome of the Governance and Security perspectives, are covered in Accounts and Organizations.

AWS documentation repeatedly returns to a handful of patterns; they recur in this section.

The running scenario, Bookshelf (a static front end, a catalog-api, an orders-api and a notifier worker that sends confirmation emails), combines several of these.