EC2 introduction

Amazon EC2 (Elastic Compute Cloud) provides resizable virtual servers in the cloud. You choose an AMI (Amazon Machine Image), instance type, key pair, and security group to launch a VM.

Core concepts

• Instance — a running virtual server
• AMI — template OS + optional software (Amazon Linux, Ubuntu)
• Instance type — vCPU, memory, network (e.g. t3.micro for learning)
• Key pair — SSH public key AWS installs; you keep the private key
• Security group — virtual firewall for instance ENI

Launch workflow (Console mental model)

1. Choose region and AMI
2. Select instance type (free tier eligible where noted)
3. Configure storage (EBS root volume—next lesson)
4. Configure security group (SSH only from your IP for learning)
5. Review and launch with a key pair

List instances via CLI

aws ec2 describe-instances \
  --query 'Reservations[].Instances[].{Id:InstanceId,State:State.Name,Type:InstanceType}' \
  --output table

Practice: Launch resources in the EC2 Console or CLI only in a sandbox account. Use t2.micro or t3.micro where free tier applies; terminate when done.

SSH to instance (after launch)

# Replace paths and IP with your sandbox values
ssh -i ~/.ssh/my-sandbox-key.pem ec2-user@203.0.113.10

Free tier: Stop or terminate instances when not learning—EBS storage may still incur cost.

Important interview questions and answers

1. Q: What is an AMI?
   A: Template image used to boot an EC2 instance with a chosen operating system.
2. Q: Security group role?
   A: Stateful firewall controlling inbound/outbound traffic to the instance network interface.

Self-check

1. What five concepts do you configure when launching EC2?
2. Why restrict SSH to your IP in a security group?

Tip: Restrict SSH to your current IP—never 0.0.0.0/0 in production or long-lived sandboxes.