Definition
Cloud computing is the on-demand delivery of computing resources — servers, storage, databases, networking, software, analytics, and intelligence — over the internet (the cloud). Instead of owning and maintaining physical data centers and servers, organizations rent access to these resources from cloud service providers, enabling rapid provisioning, scalability, and cost efficiency.
Core Characteristics
Cloud computing typically exhibits key characteristics defined by the NIST model:
- On-demand self-service: Users can provision resources as needed without human interaction with the service provider.
- Broad network access: Services are available over the network and accessible through standard mechanisms (web, mobile, API).
- Resource pooling: Provider resources are pooled to serve multiple customers using a multi-tenant model.
- Rapid elasticity: Resources can be scaled up or down quickly to match demand.
- Measured service: Resource usage is monitored, controlled, and reported, providing transparency for pay-per-use billing.
Service Models
Cloud service models describe the level of control and responsibility between the provider and the consumer:
- IaaS (Infrastructure as a Service) — Virtualized computing resources: virtual machines, storage, and networks. Example: Amazon EC2, Google Compute Engine, Microsoft Azure VMs.
- PaaS (Platform as a Service) — Platform and runtime environment for building, testing, and deploying applications without managing the underlying infrastructure. Example: Heroku, Google App Engine, Azure App Service.
- SaaS (Software as a Service) — Complete applications delivered over the web. The provider manages everything; users simply consume the software. Example: Salesforce, Google Workspace, Office 365.
Deployment Models
Choose a deployment model based on security, compliance, and business needs:
- Public cloud — Services offered over the public internet and shared across organizations.
- Private cloud — Dedicated infrastructure for a single organization, hosted on-premises or by a provider.
- Hybrid cloud — Combination of public and private clouds with orchestration between them.
- Multi-cloud — Use of multiple cloud providers to avoid vendor lock-in and optimize services.
Benefits
Cloud computing offers several advantages:
- Cost efficiency — Pay-as-you-go reduces upfront capital expense.
- Scalability — Elastic resources adapt to workload changes.
- Speed — Faster provisioning accelerates development and deployment.
- Global reach — Easily deploy applications closer to users using provider regions.
- Innovation — Access to managed services (AI/ML, analytics, serverless) speeds innovation.
Challenges and Considerations
Organizations should plan for:
- Security and compliance — Shared responsibility model requires careful controls and governance.
- Cost management — Unexpected costs can arise without proper monitoring and optimization.
- Performance — Latency and network considerations depend on architecture and region choice.
- Vendor lock-in — Design for portability or adopt multi-cloud strategies where needed.
Quick Example: Launching a VM (AWS CLI)
aws ec2 run-instances --image-id ami-0abcdef1234567890 --count 1 --instance-type t3.micro --key-name MyKeyPair --subnet-id subnet-12345678
How to Answer This in an Interview
Start with a concise definition, mention the NIST characteristics, explain service and deployment models, and finish with benefits and a short example or use case relevant to the interviewer’s industry. Keep it clear and structured.
Common Use Cases
- Web and mobile application hosting
- Data backup and disaster recovery
- Big data analytics and machine learning
- Dev/Test environments and continuous integration
By focusing on what cloud computing is, why it matters, and how it’s consumed, you’ll provide a strong, interview-ready answer.