Microsoft Azure is Microsoft's public cloud. Everything is created as a resource inside a hierarchy that controls billing, access and policy.

Services at a glance

Service	Purpose
Azure Resource Manager (ARM)	Deployment and management layer for all resources
Bicep / ARM templates	Infrastructure as Code
Azure Portal, Cloud Shell, CLI, PowerShell	Ways to manage Azure
Management groups, Subscriptions, Resource groups	Organisation hierarchy
Azure Arc	Manage on-prem and other clouds from Azure
Azure Advisor	Best-practice recommendations
Azure Migrate	Discover and migrate workloads

Cloud Concepts Refresher

Concept	Meaning
High availability	Keep a workload running despite failures (redundancy, zones)
Scalability	Add capacity: vertical (bigger VM) or horizontal (more VMs)
Elasticity	Scale out and in automatically with demand
Reliability	Recover from failure and keep working
Agility	Provision resources in minutes
Fault tolerance	Continue operating when a component fails
Disaster recovery	Restore service after a major outage (RTO / RPO)

Pricing models

CapEx: upfront spend on hardware you own
OpEx: pay-as-you-go for what you consume. Cloud is mostly OpEx
Consumption-based: pay per use, billed per second / minute / hour / GB

Shared responsibility model

Layer	On-premises	IaaS	PaaS	SaaS
Information and data	You	You	You	You
Devices, accounts, identities	You	You	You	You
Applications	You	You	You	Provider
Operating system	You	You	Provider	Provider
Network controls	You	Shared	Provider	Provider
Physical hosts / datacenter	You	Provider	Provider	Provider

Service models are covered in Cloud Computing Services.

Cloud deployment models

Public cloud: provider owns and operates the hardware, shared by many customers
Private cloud: dedicated to one organisation, on-prem or hosted
Hybrid cloud: public and private connected together (Azure Arc, Azure Stack, ExpressRoute)
Multi-cloud: more than one public provider

Global Infrastructure

Regions

A region is a set of datacenters connected by a low-latency network in a geographic area (e.g. South Africa North, West Europe). Pick a region for latency, data residency/compliance, available services and price.

Region pairs: each region is paired with another in the same geography (hundreds of km apart). Used for sequential updates and geo-redundant recovery priority
Sovereign regions: isolated instances for specific compliance needs (Azure Government, Azure China)

Availability Zones

Physically separate datacenter locations within a region, each with independent power, cooling and networking. A region that supports zones has at least 3.

Zonal services: you pin a resource to a zone (e.g. a VM)
Zone-redundant services: Azure replicates across zones for you (e.g. zone-redundant storage)

Availability Sets (older, within one datacenter)

Fault domains: share power/network (rack)
Update domains: rebooted together during maintenance

Management Hierarchy

Management Group     (policy and access for many subscriptions)
  └── Subscription   (billing + access boundary)
        └── Resource Group   (logical container, shares lifecycle)
              └── Resource   (VM, storage account, VNet ...)

Management groups: up to six levels deep, apply Azure Policy / RBAC across subscriptions
Subscription: unit of billing and scale limits. Several can sit under one account
Resource group: a resource belongs to exactly one group. Deleting the group deletes everything in it. Resources in a group can be in different regions

$ az group create --name rg-demo --location southafricanorth
$ az group list -o table
$ az group delete --name rg-demo

Azure Resource Manager (ARM)

The deployment and management layer. Every tool (Portal, CLI, PowerShell, SDKs, REST) goes through ARM.

Consistent API and access control for all resources
Infrastructure as Code with ARM templates (JSON) or Bicep (cleaner syntax, compiles to ARM)
Declarative and idempotent, with dependency ordering

resource sa 'Microsoft.Storage/storageAccounts@2023-01-01' = {
  name: 'stdemo${uniqueString(resourceGroup().id)}'
  location: resourceGroup().location
  sku: { name: 'Standard_LRS' }
  kind: 'StorageV2'
}

$ az deployment group create --resource-group rg-demo --template-file main.bicep

Ways to Manage Azure

Tool	Notes
Azure Portal	Web GUI
Cloud Shell	Browser shell with Bash or PowerShell, pre-authenticated
Azure CLI	`az` commands, cross-platform
Azure PowerShell	`Az` module cmdlets
Azure Arc	Manage on-prem, multi-cloud servers and Kubernetes from Azure
Azure Advisor	Recommendations on cost, security, reliability, performance

Service Level Agreements (SLA)

Guaranteed uptime per service, e.g. 99.9% allows about 8.7 hours downtime a year; 99.99% about 52 minutes.

Composite SLA: chaining services multiplies the SLAs, so the result is lower than either
Redundant (parallel) components raise the combined availability
Preview features generally carry no SLA