Cloud Concepts

Coming in you need no cloud background; by the end of this domain you will be able to answer the four idea-checks below on sight. AZ-900's first domain defines cloud computing as renting metered IT resources over the internet instead of buying and running your own hardware. Three threads cut across everything else in this domain: the shared responsibility model decides who secures what (Microsoft always owns the physical layer, you always own your data, identities, and access), the deployment model decides who owns and shares the infrastructure (public, private, or hybrid), and the consumption-based model decides how you pay (pay-as-you-go OpEx rather than up-front CapEx). Serverless, such as Azure Functions, is that consumption model taken to its extreme: you supply only code and pay per execution. Get these four ideas straight and the rest of the exam's cloud-concepts questions resolve quickly.

The 'benefits of using cloud services' objective tests whether you can name the right benefit, and several pairs are deliberately offered as competing answers. High availability is staying up through a failure (redundancy across availability zones); scalability is having enough capacity (scale up = vertical, scale out = horizontal); elasticity is scalability done automatically by autoscale. Reliability is recovering from a failure and continuing to run, and is a pillar of the Microsoft Azure Well-Architected Framework, while predictability splits into performance predictability (consistent experience under load) and cost predictability (forecastable, trackable spend). Security is about protecting resources through defense in depth and Microsoft Defender for Cloud; governance is about standardizing and enforcing rules at scale through Azure Policy (which audits and enforces resource configuration with policies and initiatives).

The cloud service types form a single stack distinguished by how much the provider manages for you. With IaaS (for example Azure Virtual Machines) you rent raw compute, storage, and networking and manage the operating system upward. With PaaS (for example Azure App Service or Azure SQL Database) Microsoft also manages the OS and runtime, so you supply only code and data. With SaaS (for example Microsoft 365) you consume finished software and manage nothing beyond your data, users, and access. The service type is the same coin as the shared responsibility model: choosing a higher-level service moves the responsibility line up the stack toward Microsoft, but data, accounts, and access management always stay with you.