Cloud concepts and models
Exam context: AZ-900 is 40-60 questions in 45 minutes, scaled 100-1000, 700 to pass, and it never expires. Domain 1 (cloud concepts) is 25-30% of it.
What cloud computing is
On-demand delivery of computing services (servers, storage, databases, networking, software, analytics) over the internet, pay as you go.
Core characteristics
- High availability: stays operational through failures via redundancy, zones, load balancers.
- Scalability: can grow or shrink to match demand.
- Elasticity: automatic scaling up and down (autoscaling).
- Reliability: recovers from failures predictably.
- Agility: deploy in minutes, not weeks.
- Global reach: regions worldwide for latency and data residency.
- Measured service: everything metered, billed on consumption.
The exam trap: scalability is the ability to grow; elasticity is automatic growth and shrinking. Fluctuating-workload cost questions want elasticity.
Cloud models
- Public: a third-party provider, shared multi-tenant. Azure itself.
- Private: dedicated to one org, max control. Azure Stack Hub (Azure in your own datacenter).
- Hybrid: public + private connected securely. ExpressRoute, VPN Gateway, Azure Arc.
A true hybrid cloud must include public cloud resources. Two connected private data centers is not hybrid, and yes, the exam tests exactly that.
Hybrid fits gradual migration, cloud bursting, and compliance splits.