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Cloud Concepts

This chapter establishes the vocabulary and mental models behind public cloud computing. You will learn the three core service models (IaaS, PaaS, SaaS), the deployment models (public, private, hybrid), the economic and operational benefits that drive cloud adoption, and the shared responsibility model that divides security duties between provider and customer. These fundamentals underpin every Azure service you encounter later, so a firm grasp here makes the rest of the material far easier to absorb.

Cloud Service Models: IaaS, PaaS, and SaaS

Cloud services are commonly grouped into three models that differ by how much of the technology stack the provider manages versus the customer. Moving from IaaS to PaaS to SaaS, the customer's management burden decreases while the provider takes on more. Choosing the right model is a trade-off between control and convenience.

IaaS gives the most control
Infrastructure as a Service provides virtual machines, storage, and networking; the customer manages the operating system, runtime, and applications while the provider manages the physical hardware.
PaaS targets developers
Platform as a Service supplies a managed operating system, runtime, and middleware so teams deploy application code without patching or maintaining servers.
SaaS delivers finished software
Software as a Service provides a complete application over the internet; the provider manages everything up to the app, leaving customers to manage only their data and users.
Management burden shifts by model
As you move from IaaS toward SaaS, the provider assumes more responsibility and the customer manages less of the stack.

Cloud Deployment Models

A deployment model describes where cloud resources live and who has access to them. The three primary models are public, private, and hybrid, each balancing cost, control, and compliance differently. Organizations often blend models to fit workload and regulatory needs.

Public cloud is shared and provider-owned
A third-party provider owns multi-tenant infrastructure and delivers it on demand over the internet, offering low upfront cost and vast scale.
Private cloud is dedicated
Infrastructure is used exclusively by one organization, offering greater control and isolation for strict security or compliance needs, usually at higher cost.
Hybrid cloud connects both
A hybrid model links on-premises or private environments with public cloud so workloads and data can span both, supporting gradual migration and burst scaling.
Choose based on requirements
Regulatory, cost, latency, and control requirements determine which deployment model or blend best fits a given workload.

Benefits of Cloud Computing

The cloud's appeal comes from a set of economic and operational advantages that traditional on-premises IT struggles to match. These benefits explain why organizations of all sizes migrate workloads to the cloud. Understanding each helps you justify and design cloud solutions.

Consumption-based pricing
Pay-as-you-go billing charges only for resources consumed, shifting spending from large upfront CapEx to flexible OpEx.
Scalability and elasticity
Resources scale up/down (vertical) or out/in (horizontal), and elasticity adjusts capacity automatically to match real-time demand.
High availability and reliability
Redundancy, load balancing, and backups keep applications running and recoverable, minimizing downtime and data loss.
Agility and global reach
Resources provision in minutes and can be deployed near users worldwide, accelerating innovation and reducing latency.

Scaling, Availability, and Resilience

Cloud platforms provide multiple techniques to keep applications performant and available under changing conditions and failures. Distinguishing these concepts is essential for designing dependable systems. Each addresses a different aspect of performance or continuity.

Vertical vs. horizontal scaling
Vertical scaling adds CPU/RAM to an existing resource; horizontal scaling adds more instances to share the load.
Autoscaling responds to demand
Autoscaling automatically adds capacity during spikes and removes it when demand falls, balancing performance and cost.
Fault tolerance through redundancy
Distributing resources across isolated fault domains ensures a single failure does not take down the whole service.
Disaster recovery restores operations
Replicating data and systems to other locations enables quick recovery after a major outage, minimizing downtime.
SLAs set expectations
A service-level agreement formally defines guaranteed uptime and performance, with credits if targets are missed.

The Shared Responsibility Model

Security in the cloud is a partnership: the provider secures some layers and the customer secures others, with the split depending on the service model. Misunderstanding this division is a common source of security gaps. Knowing who owns each responsibility is fundamental to safe cloud use.

Customer always owns data and identities
Regardless of service model, the customer is responsible for their data, accounts, and access management.
Provider always owns the physical layer
The cloud provider is always responsible for physical datacenter security, hardware, and the underlying network.
Responsibilities shift by model
In IaaS the customer manages the OS and up; in PaaS the provider handles the OS and runtime; in SaaS the provider manages nearly everything.
Patching depends on the model
For IaaS the customer patches the guest OS, while for PaaS and SaaS the provider handles OS and platform patching.
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Last updated: July 2026

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