Amazon EC2 (Elastic Compute Cloud) is a web service from Amazon Web Services (AWS) that lets you rent virtual servers—called “instances”—to run your applications in the cloud. Instead of buying and managing physical machines, you launch, scale, and shut down compute capacity in minutes, paying only for what you use.

Why EC2 Matters

• Flexible: Choose CPU, memory, storage, and networking to match your workload.
• Scalable: Add or remove servers quickly as traffic changes.
• Cost-effective: Multiple pricing options to fit short tests, steady apps, or big savings at scale.
• Global: Deploy in data centers (Regions/AZs) around the world for low latency and resilience.

Key Concepts (In Simple Terms)

• Instance: Your virtual server (e.g., small for blogs, large for data processing).
• AMI (Amazon Machine Image): The template for your instance (OS + preinstalled software).
• EBS (Elastic Block Store): Persistent disk for your instance so data survives reboots.
• Security Groups: Virtual firewalls that control what traffic can reach your instance.
• Key Pair: SSH/RDP credentials to log in securely.
• VPC/Subnets: Your private network in AWS where instances live.
• Elastic IP (optional): A static public IP you can keep even if you stop/replace an instance.

Instance Types (Pick What Fits)

• General Purpose (e.g., t, m): Balanced for most apps and websites.
• Compute Optimized (c): Good for CPU-heavy tasks like batch jobs or game servers.
• Memory Optimized (r, x): Ideal for in-memory databases and analytics.
• Storage Optimized (i, d): High local storage throughput for big data.
• Accelerated Computing (p, g, inf): GPUs/accelerators for AI/ML and video.

Pricing Options (How You Pay)

• On-Demand: Pay by the hour/second—great for short or unpredictable workloads.
• Savings Plans / Reserved Instances: Commit for 1–3 years to reduce costs for steady usage.
• Spot Instances: Bid for spare capacity—huge savings, but can be interrupted.
• Dedicated Hosts/Instances: Physical isolation for licensing or compliance needs.
• Free Tier: Often includes limited monthly hours on small instances for 12 months (great for learning).

Common Use Cases

• Hosting websites and APIs
• Running containers and microservices
• Training/inferencing ML models (with GPU instances)
• Batch processing and data pipelines
• Game servers, dev/test environments, CI runners

Quick Start: Launching Your First EC2

1. Pick a Region: Choose one near your users.
2. Select an AMI: Start with Amazon Linux or Ubuntu.
3. Choose Instance Type: A t3.micro is fine for small tests.
4. Configure Network: Place it in a VPC subnet; allow needed inbound ports.
5. Add Storage: EBS volume size (e.g., 8–20 GB to start).
6. Set Security Group:
   • Linux: allow SSH (port 22) from your IP
   • Windows: allow RDP (port 3389) from your IP
   • Web: allow HTTP/HTTPS (80/443) if hosting a site
7. Create/Select Key Pair: Download and keep it safe.
8. Launch & Connect: Use SSH or RDP to log in and deploy your app.

Example: Small Business Website

A bakery wants an online menu and ordering page:

• Launch a t3.small instance with an Ubuntu AMI.
• Attach a 20 GB EBS volume.
• Open 80/443 in the security group.
• Install Nginx and the app.
• Add Auto Scaling and a Load Balancer later as traffic grows.
• Optionally use an Elastic IP and attach a custom domain in Route 53.

Tips & Best Practices

• Right-size continuously: Monitor CPU/RAM and adjust instance size.
• Use Auto Scaling: Match capacity to traffic to save money.
• Keep OS updated: Patch regularly or bake updates into your AMIs.
• Back up EBS: Take snapshots; test restore.
• Use IAM roles: Avoid hardcoding access keys on instances.

Bottom line: EC2 gives you on-demand compute with fine-grained control, so you can start small, scale big, and pay only for what you need.