Cloud Concepts and Azure Architecture Review

The Cloud Concepts domain accounts for approximately 25–30% of the AZ-900 exam. Key topics include: the definition and benefits of cloud computing, the shared responsibility model, cloud service models (IaaS/PaaS/SaaS), and cloud deployment models (public/private/hybrid). The exam tests whether you understand which model is appropriate for a given scenario, not just the definitions. Pay particular attention to the six benefits of cloud computing Microsoft lists in the exam objectives.

The shared responsibility model divides security and management responsibilities between Microsoft and the customer. Microsoft always manages: physical data centres, physical network, physical hosts. Customer always manages: data, accounts, and identities. The middle layer shifts depending on service model: for IaaS, customers manage OS, network controls, and applications; for PaaS, Microsoft additionally manages the OS and middleware; for SaaS, Microsoft manages nearly everything except data and account access.

Microsoft's AZ-900 objectives define six cloud benefits: High Availability (services stay available via SLAs), Scalability (add capacity on demand), Elasticity (automatically scale up and down), Agility (deploy faster than on-premises), Geo-Distribution (deploy globally with low latency), and Disaster Recovery (replicate and fail over across regions). The exam often presents scenarios and asks which benefit best applies. Elasticity and scalability are the most frequently confused pair — elasticity is automatic adjustment; scalability is the ability to scale.

Traditional on-premises IT uses CapEx (Capital Expenditure) — upfront investment in hardware and infrastructure, depreciated over time. Cloud computing shifts to OpEx (Operational Expenditure) — pay for what you consume, period to period, with no large upfront cost. This shift benefits cash flow and reduces financial risk from over-provisioning. The AZ-900 exam may ask you to identify whether a scenario represents CapEx or OpEx, or to explain why a company migrating to Azure would see an OpEx increase while CapEx decreases.

Memorise the Azure resource hierarchy for the exam: Management Groups (top — aggregate subscriptions, apply policies) → Subscriptions (billing boundary, access control boundary) → Resource Groups (logical container for related resources) → Resources (individual services like VMs, storage accounts). A subscription belongs to exactly one management group. A resource belongs to exactly one resource group. Resource groups can contain resources from any Azure region.

Key region and availability zone facts for the exam: Azure has 60+ regions worldwide. Each region is a geographic area containing one or more data centres. Region pairs are pre-configured for disaster recovery replication, with at least 300 miles separation. Availability Zones (AZs) are physically separate data centres within a single region, each with independent power, cooling, and networking. Not all regions have AZs — the exam may test whether you know that AZs are only available in select regions (called Zone-enabled regions).

Use these exam mnemonics for service models: IaaS = You manage from the OS up (Azure VM, Azure Disks). PaaS = You manage the application and data only (Azure App Service, Azure SQL Database, Azure Functions). SaaS = You manage only data and access (Microsoft 365, Dynamics 365). Common AZ-900 trick: Azure SQL Database is PaaS (not IaaS), even though it is a database. SQL Server on a VM is IaaS. If you manage the OS, it is IaaS; if you do not, it is PaaS.

Three cloud deployment models tested in AZ-900: Public cloud — resources owned and operated by a third-party provider (Azure), shared infrastructure, pay-as-you-go. Private cloud — resources used exclusively by a single organisation, hosted on-premises or in a dedicated colocation facility, full control. Hybrid cloud — public and private cloud connected, allowing workloads to run in the most appropriate environment. The exam may test: Which deployment model allows an organisation to run sensitive data on-premises while using Azure for scalable compute? Answer: Hybrid.

Azure uses a consumption-based pricing model — you only pay for cloud services when you use them. This directly aligns to the OpEx model. Three pricing options appear in AZ-900: Pay-as-you-go (no commitment, highest per-unit price), Reserved Instances (1 or 3-year commitment, up to 72% discount), and Spot pricing (use unused Azure capacity at deep discounts, subject to eviction). The exam may also ask about the Total Cost of Ownership (TCO) Calculator, which estimates on-premises cost vs. Azure cost to build a migration business case.

These scenario types appear frequently in AZ-900 cloud concept questions:

• Which benefit? — A company needs to handle 10× more traffic during the holidays → Elasticity or Scalability.
• Which model? — A startup wants a database without managing servers → PaaS (Azure SQL Database).
• Which deployment? — A hospital must keep patient data on-site but wants to use Azure for analytics → Hybrid cloud.
• Which pricing? — A company has a VM that runs 24/7 for 3 years → Reserved Instances.

High-frequency architecture facts for last-minute revision:

• Azure Availability Zones protect against data centre failures; Region Pairs protect against regional outages.
• A resource group cannot contain another resource group.
• Resources in a resource group can be in different regions.
• Management groups can be up to 6 levels deep (not counting root).
• An Entra ID tenant can have multiple Azure subscriptions.

Test your understanding of Microsoft Azure Fundamentals (AZ-900) concepts from this lesson.

In this lesson you reviewed: the shared responsibility model and how responsibilities shift across IaaS/PaaS/SaaS, the six cloud benefits (availability, scalability, elasticity, agility, geo-distribution, disaster recovery), and the Azure resource hierarchy (management groups → subscriptions → resource groups → resources). Next up we do a condensed quick-reference review of core Azure services.