How Elastic IPs Help You Stick with One Address in AWS
4 min read
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.