What is AWS?

AWS is a collection of on-demand cloud services operated by Amazon. You pay for what you use (often per hour, per GB, or per request) instead of capital expense on hardware.

Core characteristics

• Elasticity — scale resources up or down as traffic changes
• Global reach — many regions and edge locations worldwide
• Managed services — RDS, Lambda, S3 handle ops tasks for you
• Shared responsibility — AWS secures the cloud; you secure what you put in it
• API-driven — Console, CLI, and SDKs control the same underlying APIs

Service categories (high level)

List services in your account

# Optional — requires appropriate IAM permissions
aws ec2 describe-regions --query 'Regions[].RegionName' --output table
aws s3 ls  # lists buckets if S3 read access is granted

Practice: Use the AWS Free Tier or a dedicated sandbox account. Run optional CLI steps in a terminal with aws configure using a non-production IAM user—never root keys.

Who uses AWS?

Startups, enterprises, and governments host web apps, data pipelines, ML workloads, and internal tools. Full-stack developers combine AWS with Python (boto3) or Node.js (AWS SDK v3).

Important interview questions and answers

1. Q: IaaS vs PaaS vs SaaS on AWS?
   A: EC2 is IaaS (you manage OS); Elastic Beanstalk is PaaS; WorkDocs is SaaS—AWS spans all layers.
2. Q: Is AWS only for big companies?
   A: Free tier and pay-as-you-go make it accessible for learning and small projects—with billing guardrails.

Self-check

1. Name three AWS service categories and one example each.
2. What does shared responsibility mean in one sentence?

Tip: Group services by compute, storage, database, networking, and security when studying.