Cloud Computing Fundamentals
What to know
Cloud computing delivers compute, storage, and networking as metered services over a network. Candidates must be fluent in the service models (IaaS, PaaS, SaaS) and deployment models (public, private, hybrid, community), plus the essential characteristics: on-demand self-service, broad network access, resource pooling, rapid elasticity, and measured service. Understand the shared responsibility boundary: the provider secures the physical layer and the hypervisor; the customer secures what they put in the cloud (data, identities, configurations).
Know the resilience vocabulary precisely. Region is a geographic area; zone is an isolated datacenter cluster within a region. High availability means surviving a zone failure; disaster recovery means surviving a region failure. Vertical scaling adds power to one instance; horizontal scaling adds instances. Distinguish elasticity (automatic, demand-driven) from scalability (capacity to grow).
Traps
Questions love to blur the lines. "The provider patches the guest OS" is false under IaaS. "Multi-zone equals disaster recovery" is false - it is HA. "Elasticity and scalability are the same" is false. Watch for wording that swaps fault tolerance (zero downtime, expensive) with high availability (brief failover).
Rule of thumb
Ask who manages the layer and what failure am I surviving. If the failure is a single datacenter, design multi-zone. If it is a whole geography, design multi-region with replicated data.
Worked example
An app must stay online if one datacenter fails, with minimal cost. Answer: deploy across two zones in one region with a load balancer - that is HA. Adding a second region is DR and adds cost and complexity the requirement does not demand.