How Elastic IPs Help You Stick with One Address in AWS

Arjun was building a secure web app on AWS using EC2. Everything worked perfectly… until one day his IP address changed.

“Wait, why did my public IP change after a restart?” he asked in panic.
“How will my users find my app now?”

That’s when he discovered the solution: Elastic IPs.

🧠 What Is an Elastic IP?

An Elastic IP (EIP) is a static, public IPv4 address provided by AWS that you own and can remap anytime to any EC2 instance in your account.

Think of it as:

“Your permanent digital street address on the internet.”

Unlike normal public IPs (which change when you stop/start an EC2), Elastic IPs stick around.

🆚 Elastic IP vs. Public IP — What’s the Difference?

Feature	Public IP (Default)	Elastic IP
Assigned	Automatically by AWS	Manually by you
Persistent?	❌ No (changes on stop/start)	✅ Yes (permanent until released)
Cost	Free	Free if attached
Reusable?	❌ No	✅ Yes (can reassign to other instances)

📘 SAA Tip: If the question mentions "static IP address", "fixed IP", or "IP persistence" — think Elastic IP.

🎯 Why Use Elastic IPs?

Arjun made a list of use cases:

🔗 Need a fixed IP for DNS mapping
- Point your domain to the same IP—even if the EC2 instance changes
🔐 Whitelisting for firewalls or partner APIs
- External systems often require a static IP
🔄 Recover quickly from instance failure
- Stop an EC2 → start another → remap the same EIP = fast failover

🔧 How Arjun Set Up an Elastic IP

Went to EC2 Dashboard → Elastic IPs
Clicked “Allocate Elastic IP”
Got a new public IPv4 address from AWS
Attached it to his EC2 instance

💡 If the instance stopped and restarted, the EIP remained the same — no disruptions!

🔁 Reassigning an EIP: Disaster Recovery Superpower

Later, when Arjun’s server crashed, he launched a new EC2 instance.

Instead of changing DNS or informing his clients of a new IP…

He simply reassigned the same Elastic IP to the new instance — in seconds.

✅ No DNS updates
✅ No partner-side firewall changes
✅ Smooth recovery

💸 Is It Free?

Elastic IPs are free under one condition:

You must attach them to a running instance.

❌ You’ll be charged if:

The EIP is unattached
Or you have more than one EIP per instance

📘 AWS does this to discourage hoarding of public IPv4 addresses.

❗ Important EIP Rules to Know

Rule	Why It Matters
One EIP per instance by default	Keeps address management simple
Can be remapped anytime	Enables fast failover
Only IPv4 supported	No Elastic IPv6 yet
Not tied to instance lifecycle	Survives stop/terminate events
Limited per region (usually 5)	You can request more, if needed

🧠 Summary for AWS SAA Exam

Concept	Description
Elastic IP (EIP)	Static public IPv4 address in AWS
Main Benefit	Remains fixed, even if EC2 is stopped or replaced
Use Case	DNS mapping, whitelisting, failover
Cost	Free if used, charged if idle
Common Services	EC2, NAT Gateway, Load Balancers (rarely)

🚀 Arjun’s Final Setup

Users
  ↓
Elastic IP (Fixed Public IP)
  ↓
EC2 Instance (Web Server)

When the instance failed:

Users
  ↓
Same Elastic IP
  ↓
New EC2 Instance (Same role)

“Elastic IP gave me reliability, control, and peace of mind. I can sleep through restarts now!” Arjun said proudly.