IaaS vs PaaS vs SaaS
IaaS: raw infrastructure (VMs, networks). PaaS: managed platform to deploy apps. SaaS: finished software you consume. Example: AWS EC2 (IaaS), Heroku (PaaS), Gmail (SaaS).
AWS core services
Compute: EC2/Lambda/ECS/EKS. Storage: S3/EBS/EFS. Databases: RDS/DynamoDB. Networking: VPC/Route53. IAM for identities/permissions.
GCP and Azure equivalents
Compute: GCE/Azure VMs, Cloud Functions/Azure Functions, GKE/AKS. Storage: Cloud Storage/Azure Blob. Databases: Cloud SQL/CosmosDB.
Serverless pros/cons
Pros: no servers to manage, auto-scale, pay-per-use. Cons: cold starts, stateless, vendor limits. Good for event-driven workloads/APIs.
VPC, subnets, and security groups
Isolated network in cloud with public/private subnets. Security groups act as firewall rules. Use NAT gateways for private subnet outbound internet.
Cost optimization
Right-size instances, use reserved/savings plans, autoscale, lifecycle policies for storage, monitor with cost explorer/budgets.
Multi-cloud and portability
Use containers/Kubernetes, IaC, abstraction layers to reduce vendor lock-in. Balance complexity vs benefit.
High availability and multi-region
Design across AZs/regions with health checks, failover (Route53), and data replication. Understand trade-offs in consistency and latency.
IAM best practices
Use least privilege, roles over long-lived keys, resource-level policies, and scoped access. Rotate and audit regularly.
S3 storage classes & lifecycle
Standard, IA, One Zone-IA, Glacier/Deep Archive. Use lifecycle rules to transition/expire data and reduce cost.
Auto Scaling Groups
Scale EC2 fleets based on metrics/schedules. Combine with Load Balancers and launch templates; test scale-in protection.
Pricing: On-demand vs Reserved vs Spot
Reserved/Savings Plans for steady workloads; Spot for fault-tolerant batch; mix instance types to maximize savings and availability.
VPC peering and Transit Gateway
Use peering for simple VPC connectivity; Transit Gateway for scalable hub-and-spoke across accounts/regions. Mind CIDR overlap and routing.
Data transfer costs
Cross-AZ/region transfer can be expensive. Prefer same-AZ traffic, use CloudFront, and compress payloads to control egress.