Cloud Computing Fundamentals: IaaS, PaaS, SaaS & Core Concepts

IaaS: rent virtual machines, storage and networks; you manage the OS up (AWS EC2, Azure VMs). PaaS: the provider runs the platform; you deploy code (Heroku, Google App Engine, Azure App Service). SaaS: finished software over the internet (Gmail, Microsoft 365, Salesforce).

The provider secures the cloud itself (data centers, hardware, hypervisor). The customer secures what they put in it (data, identities, access, configuration). The customer's share is largest in IaaS and smallest in SaaS.

Public: shared provider infrastructure open to anyone. Private: dedicated to one organization. Hybrid: public and private connected together. Community: shared by organizations with common needs.

On-demand self-service Broad network access Resource pooling (multi-tenancy) Rapid elasticity Measured service (pay for what you use)

Scalability: the ability to handle more load by adding resources. Elasticity: adding and removing resources automatically as demand rises and falls.

Vertical (scale up): a bigger machine with more CPU or RAM; has a ceiling. Horizontal (scale out): more machines behind a load balancer; nearly unlimited and more fault tolerant.

A region is a geographic area (e.g. us-east-1). An availability zone is one or more isolated data centers within a region, with separate power and networking. Spreading across zones gives high availability.

Distributes incoming traffic across multiple servers, routes around unhealthy ones using health checks, and enables horizontal scaling.

A network of edge servers that caches content close to users to cut latency (e.g. CloudFront, Cloudflare)

You deploy functions or services and the provider handles servers, scaling and patching; you pay per request or execution time (AWS Lambda, Azure Functions, Google Cloud Functions).

VMs virtualize hardware and each runs a full guest OS. Containers share the host OS kernel and package just the app and its dependencies, so they are lighter and start in seconds.

An open-source system that orchestrates containers: scheduling, scaling, self-healing and rolling updates across a cluster

Type 1 (bare metal) runs directly on hardware (VMware ESXi, Hyper-V); used in data centers. Type 2 (hosted) runs on top of an OS (VirtualBox, VMware Workstation).

Object: files with metadata in a flat namespace accessed over HTTP; massively scalable (S3, Azure Blob). Block: raw disk volumes for VMs and databases (EBS). File: shared file system with folders (EFS, Azure Files).

Owning servers is capital expenditure (large up-front purchase). Cloud shifts spending to operational expenditure (pay as you go).

High availability: minimal downtime, with quick failover (e.g. 99.99% uptime). Fault tolerance: keeps running with no interruption even when a component fails, through full redundancy.

Defining servers, networks and other resources in version-controlled configuration files that tools apply automatically (Terraform, AWS CloudFormation, Bicep). It makes environments repeatable.

Compute VMs: EC2 = Azure Virtual Machines = Compute Engine. Object storage: S3 = Azure Blob Storage = Cloud Storage. Functions: Lambda = Azure Functions = Cloud Functions.

Dependence on one provider's proprietary services that makes switching providers costly. Containers, open standards and multi-cloud designs reduce it.