AWS EC2

Amazon Elastic Compute Cloud (EC2) provides resizable compute capacity in the cloud.

Advanced patterns (Auto Scaling, Spot Fleets, Session Manager, Instance Connect, IMDS, Placement Groups, scheduled scaling): see instance-management.md.

Table of Contents

• Core Concepts
• Common Patterns
• CLI Reference
• Best Practices
• Troubleshooting
• References

Core Concepts

Instance Types

| Category | Example | Use Case | |----------|---------|----------| | General Purpose | t3, m6i, t4g (Graviton) | Web servers, dev environments | | Compute Optimized | c6i, c7g (Graviton) | Batch processing, gaming | | Memory Optimized | r6i, r7g (Graviton) | Databases, caching | | Storage Optimized | i3, d3 | Data warehousing | | Accelerated | p4d, g5 | ML, graphics |

Graviton (ARM) instances (t4g, m7g, c7g, r7g) are ~20% cheaper than x86 equivalents for the same performance — worth considering for new workloads.

Purchasing Options

| Option | Description | |--------|-------------| | On-Demand | Pay by the hour/second | | Reserved | 1-3 year commitment, up to 72% discount | | Spot | Unused capacity, up to 90% discount — can be interrupted with 2-minute notice | | Savings Plans | Flexible commitment-based discount |

AMI (Amazon Machine Image)

Template containing OS, software, and configuration for launching instances. Use SSM Parameter Store to look up the latest official AMIs rather than hardcoding IDs:

bash
# Latest Amazon Linux 2 AMI
aws ssm get-parameter \
  --name /aws/service/ami-amazon-linux-latest/amzn2-ami-hvm-x86_64-gp2 \
  --query 'Parameter.Value' --output text

# Latest Amazon Linux 2023
aws ssm get-parameter \
  --name /aws/service/ami-amazon-linux-latest/al2023-ami-kernel-default-x86_64 \
  --query 'Parameter.Value' --output text

# Latest Ubuntu 22.04
aws ssm get-parameter \
  --name /aws/service/canonical/ubuntu/server/22.04/stable/current/amd64/hvm/ebs-gp2/ami-id \
  --query 'Parameter.Value' --output text

Security Groups

Virtual firewalls controlling inbound and outbound traffic. Changes take effect immediately — no restart required.

Common Patterns

Launch an Instance

bash
# Create key pair
aws ec2 create-key-pair \
  --key-name my-key \
  --query 'KeyMaterial' \
  --output text > my-key.pem
chmod 400 my-key.pem

# Create security group
aws ec2 create-security-group \
  --group-name web-server-sg \
  --description "Web server security group" \
  --vpc-id vpc-12345678

# Allow SSH and HTTP
aws ec2 authorize-security-group-ingress \
  --group-id sg-12345678 \
  --protocol tcp \
  --port 22 \
  --cidr 10.0.0.0/8

aws ec2 authorize-security-group-ingress \
  --group-id sg-12345678 \
  --protocol tcp \
  --port 80 \
  --cidr 0.0.0.0/0

# Launch instance
aws ec2 run-instances \
  --image-id ami-0123456789abcdef0 \
  --instance-type t3.micro \
  --key-name my-key \
  --security-group-ids sg-12345678 \
  --subnet-id subnet-12345678 \
  --associate-public-ip-address \
  --tag-specifications 'ResourceType=instance,Tags=[{Key=Name,Value=web-server}]'

# Wait until running, then get IP
aws ec2 wait instance-running --instance-ids i-1234567890abcdef0
aws ec2 describe-instances \
  --instance-ids i-1234567890abcdef0 \
  --query 'Reservations[].Instances[].PublicIpAddress' --output text

boto3:

python
import boto3

ec2 = boto3.resource('ec2')

instances = ec2.create_instances(
    ImageId='ami-0123456789abcdef0',
    InstanceType='t3.micro',
    KeyName='my-key',
    SecurityGroupIds=['sg-12345678'],
    SubnetId='subnet-12345678',
    MinCount=1,
    MaxCount=1,
    TagSpecifications=[{
        'ResourceType': 'instance',
        'Tags': [{'Key': 'Name', 'Value': 'web-server'}]
    }]
)

instance = instances[0]
instance.wait_until_running()
instance.reload()
print(f"Instance ID: {instance.id}")
print(f"Public IP: {instance.public_ip_address}")

User Data Script

> OS package manager note: > - Amazon Linux 2: use amazon-linux-extras install nginx1 -y — yum install nginx fails because nginx is not in the default AL2 repos > - Amazon Linux 2023: use dnf install -y nginx > - Ubuntu: use apt-get install -y nginx > - Amazon Linux 2 / RHEL: httpd (Apache) is always available via yum install -y httpd

bash
# Amazon Linux 2 — nginx via amazon-linux-extras
aws ec2 run-instances \
  --image-id ami-0123456789abcdef0 \
  --instance-type t3.micro \
  --key-name my-key \
  --security-group-ids sg-12345678 \
  --subnet-id subnet-12345678 \
  --user-data '#!/bin/bash
amazon-linux-extras install nginx1 -y
systemctl start nginx
systemctl enable nginx
'

# Amazon Linux 2 — httpd (Apache, simpler alternative)
# --user-data '#!/bin/bash
# yum install -y httpd
# systemctl start httpd
# systemctl enable httpd
# echo "<h1>Hello from $(hostname -f)</h1>" > /var/www/html/index.html
# '

Attach IAM Role

bash
# Create instance profile
aws iam create-instance-profile \
  --instance-profile-name web-server-profile

aws iam add-role-to-instance-profile \
  --instance-profile-name web-server-profile \
  --role-name web-server-role

# Launch with profile
aws ec2 run-instances \
  --image-id ami-0123456789abcdef0 \
  --instance-type t3.micro \
  --iam-instance-profile Name=web-server-profile \
  ...

Create AMI from Instance

bash
aws ec2 create-image \
  --instance-id i-1234567890abcdef0 \
  --name "my-custom-ami-$(date +%Y%m%d)" \
  --description "Custom AMI with web server" \
  --no-reboot

Auto Scaling Group with Spot (Modern Approach)

The recommended way to use Spot Instances at scale is via Auto Scaling Groups with a mixed-instances policy — not the legacy request-spot-instances API. This supports instance diversification to minimize interruptions.

See instance-management.md for the full setup. Quick example:

bash
# 1. Create launch template with IMDSv2
aws ec2 create-launch-template \
  --launch-template-name my-lt \
  --launch-template-data '{
    "ImageId": "ami-0123456789abcdef0",
    "SecurityGroupIds": ["sg-12345678"],
    "IamInstanceProfile": {"Name": "my-profile"},
    "MetadataOptions": {"HttpTokens": "required", "HttpEndpoint": "enabled"}
  }'

# 2. Create ASG with mixed-instances (Spot + On-Demand diversification)
aws autoscaling create-auto-scaling-group \
  --auto-scaling-group-name my-asg \
  --min-size 0 --max-size 20 --desired-capacity 2 \
  --vpc-zone-identifier "subnet-111,subnet-222" \
  --mixed-instances-policy '{
    "LaunchTemplate": {
      "LaunchTemplateSpecification": {"LaunchTemplateName": "my-lt", "Version": "$Latest"},
      "Overrides": [
        {"InstanceType": "c5.xlarge"},
        {"InstanceType": "c5.2xlarge"},
        {"InstanceType": "c5a.xlarge"}
      ]
    },
    "InstancesDistribution": {
      "OnDemandBaseCapacity": 0,
      "OnDemandPercentageAboveBaseCapacity": 0,
      "SpotAllocationStrategy": "capacity-optimized"
    }
  }'

EBS Volume Management

bash
# Create volume
aws ec2 create-volume \
  --availability-zone us-east-1a \
  --size 100 \
  --volume-type gp3 \
  --iops 3000 \
  --throughput 125 \
  --encrypted

# Attach to instance
aws ec2 attach-volume \
  --volume-id vol-12345678 \
  --instance-id i-1234567890abcdef0 \
  --device /dev/sdf

# Create snapshot
aws ec2 create-snapshot \
  --volume-id vol-12345678 \
  --description "Daily backup"

CLI Reference

Instance Management

| Command | Description | |---------|-------------| | aws ec2 run-instances | Launch instances | | aws ec2 describe-instances | List instances | | aws ec2 start-instances | Start stopped instances | | aws ec2 stop-instances | Stop running instances | | aws ec2 reboot-instances | Reboot instances | | aws ec2 terminate-instances | Terminate instances | | aws ec2 modify-instance-attribute | Modify instance settings |

Security Groups

| Command | Description | |---------|-------------| | aws ec2 create-security-group | Create security group | | aws ec2 describe-security-groups | List security groups | | aws ec2 authorize-security-group-ingress | Add inbound rule | | aws ec2 revoke-security-group-ingress | Remove inbound rule | | aws ec2 authorize-security-group-egress | Add outbound rule |

AMIs

| Command | Description | |---------|-------------| | aws ec2 describe-images | List AMIs | | aws ec2 create-image | Create AMI from instance | | aws ec2 copy-image | Copy AMI to another region | | aws ec2 deregister-image | Delete AMI |

EBS Volumes

| Command | Description | |---------|-------------| | aws ec2 create-volume | Create EBS volume | | aws ec2 attach-volume | Attach to instance | | aws ec2 detach-volume | Detach from instance | | aws ec2 create-snapshot | Create snapshot | | aws ec2 modify-volume | Resize/modify volume |

Best Practices

Security

• Use IAM roles instead of access keys on instances
• Restrict security groups — principle of least privilege
• Use private subnets for backend instances
• Enable IMDSv2 to prevent SSRF attacks
• Encrypt EBS volumes at rest

bash
# Require IMDSv2 on existing instance
aws ec2 modify-instance-metadata-options \
  --instance-id i-1234567890abcdef0 \
  --http-tokens required \
  --http-endpoint enabled

Performance

• Right-size instances — monitor and adjust
• Use EBS-optimized instances
• Choose appropriate EBS volume type (gp3 is the default good choice; io2 for high IOPS)
• Use placement groups for low-latency networking (see instance-management.md)

Cost Optimization

• Use Spot Instances for fault-tolerant workloads (batch, ML training, CI)
• Stop/terminate unused instances
• Use Reserved Instances or Savings Plans for steady-state workloads
• Delete unused EBS volumes and snapshots
• Consider Graviton (t4g, m7g, c7g) — ~20% cheaper for same performance

Reliability

• Use Auto Scaling Groups for high availability (see instance-management.md)
• Deploy across multiple AZs
• Use Elastic Load Balancer for traffic distribution
• Implement health checks

Troubleshooting

Cannot SSH to Instance

First: identify the error type — it points to different root causes:

| Error | What it means | Primary suspects | |-------|--------------|-----------------| | Connection refused | Network is reachable, but SSH daemon is not listening | sshd crashed, sshd not installed, OS firewall (ufw/iptables) blocking, wrong port | | Connection timed out | Packets never arrive | Security group blocks port 22, NACL blocks traffic, no public IP, wrong IP | | Permission denied | Connected, but auth failed | Wrong key file, wrong username, key not authorized |

Common username by OS:

| OS | Default SSH user | |----|-----------------| | Amazon Linux 2 / 2023 | ec2-user | | Ubuntu | ubuntu | | Debian | admin | | CentOS / RHEL | ec2-user or centos | | Windows | Administrator |

Diagnostic commands:

bash
# 1. Check instance state and public IP
aws ec2 describe-instances \
  --instance-ids i-1234567890abcdef0 \
  --query "Reservations[].Instances[].{State:State.Name,PublicIP:PublicIpAddress,StatusChecks:State.Name}"

# 2. Check instance status (system + instance checks)
aws ec2 describe-instance-status --instance-ids i-1234567890abcdef0

# 3. Check security group rules for port 22
aws ec2 describe-security-groups \
  --group-ids sg-12345678 \
  --query "SecurityGroups[].IpPermissions[?ToPort==\`22\`]"

# 4. Get console output to see boot logs, sshd errors, OOM events
aws ec2 get-console-output \
  --instance-id i-1234567890abcdef0 \
  --latest \
  --query Output --output text

If connection refused — get inside via Session Manager to fix sshd:

bash
# Requires SSM agent on instance + AmazonSSMManagedInstanceCore policy
aws ssm start-session --target i-1234567890abcdef0

# Once inside, diagnose:
systemctl status ssh        # Ubuntu
systemctl status sshd       # Amazon Linux
df -h                       # Check disk full
sudo sshd -t                # Test sshd config for syntax errors
sudo journalctl -u ssh -n 50  # Recent sshd logs

Use Session Manager instead of SSH (no open ports, no key pair needed):

bash
aws ssm start-session --target i-1234567890abcdef0

# Port forwarding via SSM
aws ssm start-session \
  --target i-1234567890abcdef0 \
  --document-name AWS-StartPortForwardingSession \
  --parameters '{"portNumber":["22"],"localPortNumber":["2222"]}'

Instance Won't Start

Causes:

• Reached instance limits
• Insufficient capacity in AZ
• EBS volume issue
• Invalid AMI

bash
# Check instance state reason
aws ec2 describe-instances \
  --instance-ids i-1234567890abcdef0 \
  --query "Reservations[].Instances[].StateReason"

Instance Unreachable

bash
# Check instance status
aws ec2 describe-instance-status \
  --instance-ids i-1234567890abcdef0

# Get console output
aws ec2 get-console-output \
  --instance-id i-1234567890abcdef0 \
  --latest

# Get screenshot (for Windows/GUI issues)
aws ec2 get-console-screenshot \
  --instance-id i-1234567890abcdef0

High CPU/Memory

bash
# Enable detailed monitoring
aws ec2 monitor-instances \
  --instance-ids i-1234567890abcdef0

# Check CloudWatch metrics (cross-platform date command)
START=$(date -u -v-1H +%Y-%m-%dT%H:%M:%SZ 2>/dev/null || date -u --date='1 hour ago' +%Y-%m-%dT%H:%M:%SZ)
aws cloudwatch get-metric-statistics \
  --namespace AWS/EC2 \
  --metric-name CPUUtilization \
  --dimensions Name=InstanceId,Value=i-1234567890abcdef0 \
  --start-time "$START" \
  --end-time "$(date -u +%Y-%m-%dT%H:%M:%SZ)" \
  --period 300 \
  --statistics Average

References

• EC2 User Guide
• EC2 API Reference
• EC2 CLI Reference
• boto3 EC2