EC2 Fundamentals: Complete Guide to AMI, Instances, and EBS

Key Takeaway

EC2 is AWS's virtual server service that lets you rent compute capacity in the cloud. Use AMIs as server templates, EBS for persistent storage, and instances for actual computing workloads.

Component	Purpose	Key Characteristic
AMI	Server template	OS + software + config, region-bound
Instance	Running virtual server	CPU, memory, networking
EBS	Persistent storage	Independent of instance, AZ-bound
Instance Store	Ephemeral storage	Physical disk, deleted on stop

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What is EC2?

Amazon EC2 (Elastic Compute Cloud) is a service that lets you create and manage virtual servers (instances) in the cloud.

Core Benefits of EC2

EC2 Advantages:
├── Elasticity: Create/delete instantly as needed
├── Scalability: Scale to hundreds of instances in minutes
├── Flexibility: Choose from various OS and instance types
├── Cost: Pay only for what you use (per-second billing)
└── Integration: Works with VPC, EBS, IAM, and other AWS services

EC2 Component Architecture

EC2 Instance Structure:
┌─────────────────────────────────────────────┐
│              EC2 Instance                    │
│  ┌─────────┐  ┌─────────┐  ┌─────────────┐  │
│  │   CPU   │  │ Memory  │  │ Network(ENI)│  │
│  └─────────┘  └─────────┘  └─────────────┘  │
│                                             │
│  ┌─────────────────┐  ┌─────────────────┐  │
│  │ Instance Store  │  │   EBS Volume    │  │
│  │ (Ephemeral)     │  │  (Persistent)   │  │
│  └─────────────────┘  └─────────────────┘  │
└─────────────────────────────────────────────┘
                    ↑
            Launched from AMI

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AMI (Amazon Machine Image)

What is an AMI?

An AMI is a template for creating EC2 instances. It includes the OS, applications, and configurations.

AMI Components

AMI Structure:
├── Root Volume Template
│   ├── Operating System (Amazon Linux, Ubuntu, Windows, etc.)
│   └── Applications and configurations
├── Launch Permissions
│   └── Which AWS accounts can use this AMI
└── Block Device Mapping
    └── Volume information to attach to instance

AMI Types

Type	Root Device	Characteristics
EBS-backed	EBS volume	Can stop, data persists, slower boot
Instance Store-backed	Instance store	Cannot stop, reboot only, faster boot

AMI Sources

AMI Source Types:
├── AWS-provided AMIs
│   ├── Amazon Linux 2023
│   ├── Ubuntu, Debian, RHEL
│   └── Windows Server
├── AWS Marketplace AMIs
│   └── Third-party software included (paid/free)
├── Community AMIs
│   └── Shared by other users
└── Custom AMIs
    └── Created from your own instances

Creating and Sharing AMIs

Custom AMI Creation Flow:
1. Configure EC2 instance (install software, settings)
2. Stop instance (recommended for data consistency)
3. Actions > Create Image
4. AMI created (EBS snapshot auto-generated)

AMI Sharing:
├── Share with specific accounts: Modify AMI permissions
├── Public sharing: Share with all AWS accounts
└── Copy to other regions: Use AMI Copy feature

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EC2 Instances

Instance Lifecycle

Instance States:
pending → running ⟷ stopping → stopped
              ↓
         shutting-down → terminated

State Details:
├── pending: Starting (no charge)
├── running: Running (charged)
├── stopping: Stopping (EBS-backed only)
├── stopped: Stopped (no instance charge, EBS charged)
├── shutting-down: Terminating
└── terminated: Terminated (no charges)

Stop vs Terminate vs Reboot

Action	EBS Data	Instance Store	Public IP	Private IP
Reboot	Retained	Retained	Retained	Retained
Stop	Retained	Lost	Released	Retained
Terminate	Configurable	Lost	Released	Released

Instance Type Naming Convention

Instance Type Example: m5.xlarge

m    5    .    xlarge
│    │         │
│    │         └── Size (nano, micro, small, medium, large, xlarge, 2xlarge...)
│    └── Generation (higher = newer)
└── Family (purpose)

Families:
├── General Purpose: t, m, a
├── Compute Optimized: c
├── Memory Optimized: r, x, z
├── Storage Optimized: d, i, h
├── Accelerated Computing: p, g, inf, trn
└── HPC: hpc

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EBS (Elastic Block Store)

What is EBS?

EBS is persistent block storage that attaches to EC2 instances. Data persists even when instances are stopped or terminated.

Key EBS Characteristics

EBS Features:
├── Network-attached: Connected via network, not physical
├── AZ-bound: Can only attach to instances in same AZ
├── Resizable: Can expand size while running
├── Snapshots: Backup to S3, restore to other AZ/region
├── Encryption: Encrypt data at rest with KMS
└── Multi-Attach: Only io1/io2 support Multi-Attach

EBS Volume Types

Type	Use Case	IOPS	Throughput	Best For
gp3	General SSD	16,000	1,000MB/s	Most workloads
gp2	General SSD	16,000	250MB/s	Legacy, prefer gp3
io2	Provisioned IOPS	256,000	4,000MB/s	Databases
io1	Provisioned IOPS	64,000	1,000MB/s	Legacy, prefer io2
st1	Throughput HDD	500	500MB/s	Big data, logs
sc1	Cold HDD	250	250MB/s	Archive

EBS Snapshots

EBS Snapshots:
├── Stored in S3 (managed, no direct access)
├── Incremental backup (only changed blocks)
├── Can restore to different AZ/region
├── Foundation for AMI creation
└── Shareable (other accounts, public)

Snapshot Best Practices:
├── Create regular snapshots (use AWS Backup)
├── When creating volume from snapshot, can choose different AZ
└── Can create encrypted volume from unencrypted snapshot

Root Volume Deletion Behavior

EBS Behavior on Instance Termination:
├── Root Volume: Default "Delete on Termination" = Yes
│   └── Automatically deleted on termination
├── Additional Volumes: Default "Delete on Termination" = No
│   └── Retained after termination

Important: Set root volume to "Delete on Termination" = No
           if you need to preserve data!

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Instance Store vs EBS

Comparison Table

Feature	Instance Store	EBS
Connection	Physical disk (direct)	Network (virtual)
Data Persistence	Ephemeral (lost on stop/terminate)	Persistent (independent of instance)
Performance	Very high (physical disk)	High (network latency)
Resize	Not possible	Possible (even while running)
Snapshots	Not possible	Possible
Detach/Reattach	Not possible	Possible
Cost	Included in instance price	Separate charge

Use Cases

Use Instance Store for:
├── Buffers, caches, temporary data
├── High-performance temporary storage needs
├── Data that can be lost
└── Examples: HPC scratch disk, Redis cache

Use EBS for:
├── Databases (persistent data)
├── Application data
├── Boot volumes (OS)
└── Most workloads

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EC2 Metadata and User Data

Instance Metadata

Instances can query their own information from inside.

# Metadata endpoint (IMDSv1)
curl http://169.254.169.254/latest/meta-data/

# Available information:
├── instance-id
├── instance-type
├── ami-id
├── public-ipv4
├── local-ipv4
├── iam/security-credentials/<role-name>  # IAM role temp credentials
└── ...

User Data

Scripts that run automatically when an instance starts.

#!/bin/bash
# User Data example
yum update -y
yum install -y httpd
systemctl start httpd
systemctl enable httpd
echo "Hello from EC2" > /var/www/html/index.html

User Data Characteristics:
├── Runs only on first boot (default)
├── Runs as root
├── Max 16KB
├── Passed as Base64 encoded
└── Log location: /var/log/cloud-init-output.log

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Security Groups

What are Security Groups?

Security Groups are virtual firewalls for EC2 instances. They control inbound/outbound traffic.

Security Group Characteristics:
├── Stateful: Response traffic automatically allowed
├── Allow rules only (no Deny rules)
├── Default inbound: All traffic blocked
├── Default outbound: All traffic allowed
├── Can attach to multiple instances
└── Multiple SGs can attach to one instance

Security Group Rule Examples

Type	Protocol	Port	Source	Purpose
SSH	TCP	22	My IP	Admin access
HTTP	TCP	80	0.0.0.0/0	Web server
HTTPS	TCP	443	0.0.0.0/0	Web server (SSL)
Custom	TCP	3306	sg-xxx	RDS access (SG reference)

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SAA-C03 Exam Focus Points

Common Question Types

Topic	Key Point
Data Persistence	EBS = persistent, Instance Store = ephemeral
AMI Region	AMI is region-bound, must copy for other regions
Instance Stop	EBS data retained, instance store lost, Public IP released
Boot Volume	Only gp2, gp3, io1, io2 allowed (no HDD)
Metadata	Query at 169.254.169.254, includes IAM role credentials
Security Groups	Stateful, allow only, can reference other SGs

Common Exam Traps

❌ Instance store data persists after reboot
   → Reboot retains data, but stop/terminate deletes it

❌ AMI can be used directly in another region
   → AMI is region-bound, must copy first

❌ EBS volume can attach to instance in different AZ
   → EBS is AZ-bound, use snapshot to restore in another AZ

❌ Security groups support Deny rules
   → Security groups allow only, NACLs support Deny

❌ st1 volume can be used as boot volume
   → HDD (st1, sc1) cannot be boot volumes

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Frequently Asked Questions

Q: Am I charged when I stop an EC2 instance?

Instance charges stop. However, charges continue for attached EBS volumes and Elastic IPs (if not associated).

Q: What's the difference between AMI and snapshot?

A snapshot is a backup of an EBS volume. An AMI consists of snapshot + metadata (launch permissions, block device mapping). You can launch instances directly from an AMI, but from a snapshot you must first create a volume.

Q: Can I reduce EBS volume size?

No, EBS volumes can only be expanded. To reduce size, create a smaller volume and copy the data.

Q: How do I know if an instance type has instance store?

Instance types with 'd' in the name have instance store. Examples: m5d.large, c5d.xlarge, r5d.4xlarge. You can also check in the AWS console or documentation.

Q: What is EBS Multi-Attach?

A feature that attaches io1/io2 volumes to multiple instances in the same AZ simultaneously. Requires a cluster file system, supports up to 16 instances. Standard file systems risk data corruption, so use with caution.

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Summary

EC2 is AWS's core compute service. Key points:

1. AMI: Server template, region-bound, based on EBS snapshots
2. Instance: Virtual server, understand stop/terminate/reboot behavior
3. EBS: Persistent storage, AZ-bound, backup with snapshots
4. Instance Store: Ephemeral storage, high performance, deleted on stop
5. Security Groups: Stateful firewall, allow rules only

Next, learn about EC2 Instance Type Selection Guide and EC2 Pricing Options Comparison to complete your EC2 knowledge.