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Microsoft Azure Fundamentals — Free Essentials

Key facts distilled from CertKata's AZ-900 question bank. Free to read — no account needed.

CapEx vs. OpEx, and elasticity

CapEx = upfront investment in physical infrastructure; OpEx = ongoing pay-as-you-go spend. Cloud shifts you toward OpEx. Scalability = ability to increase/decrease resources; elasticity = doing so automatically in response to real-time demand. Consumption-based pricing means you pay only for what you actually use.

Regions, Availability Zones, region pairs

Region and availability zone hierarchy: a region contains multiple availability zones, each backed by one or more data centersREGIONAZ-1Data centerData centerAZ-2Data centerData centerAZ-3Data centerData centereach AZ: one or more independent data centers

A Region is a geographic area with one or more data centers on a low-latency network. Availability Zones are physically separate locations within a Region (independent power/cooling/networking) — the building block of in-Region high availability. Azure pairs most Regions within a geography for staggered updates and prioritized recovery.

Azure Policy vs. RBAC vs. resource locks

Azure Policy: governs WHAT configurations resources may have (e.g. allowed Regions, required tags) — effects include Audit and Deny. RBAC: governs WHO can do WHAT (role assignments at management group / subscription / resource group / resource scope, inherited downward). Resource locks (CanNotDelete / ReadOnly) sit above RBAC — even an Owner must remove the lock first.

Service models and shared responsibility

Shared responsibility model: providers are always responsible for physical and host infrastructure, customers are always responsible for their data and access configuration, and the exact boundary shifts with the service modelPROVIDERalways responsible forPhysical facilitiesHostinfrastructureVirtualizationlayerCUSTOMERalways responsible forDataIdentity &accessResourceconfigurationIaaSPaaSSaaSshown at PaaS — shifts toward IaaS or SaaS

IaaS (e.g. a VM): customer manages OS upward. PaaS (e.g. Azure SQL Database): Microsoft manages the OS/engine, customer manages data and app config. SaaS (e.g. Microsoft 365): customer manages mainly data and access. Across every model, the customer ALWAYS keeps their data, devices, and identities; Microsoft ALWAYS keeps physical data center security.

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