Elastic Network Interface.
ENI stands for Elastic Network Interface.
Imagine your EC2 server is a house 🏠.
To send letters or get pizza delivered, your house needs an address 🏷.
An ENI is like that address — it’s how the internet and other machines know where to find your house in the cloud.
You can take this address and move it to another house if you move — that’s why it’s elastic.
Why it’s useful:
Extra addresses – Your cloud house can have more than one address for different guests.
Move around – If one house breaks, you can move the same address to another house and people will still find you.
Private or public – You can have a secret address (private IP) for friends and a public one for everyone else.
💡 In short:
EC2 = House 🏠 ENI = Address 📍 Cloud = The whole neighborhood ☁️
Elastic IP (EIP)
Think of an Elastic IP as a special public phone number 📞 in the cloud.
Anyone in the world can use it to call your cloud computer.
Private IP
A Private IP is like a secret house address 🏠 inside your neighborhood (VPC).
Only your friends inside the neighborhood can find it — strangers can’t.
AWS says:
“If you want a public phone number (Elastic IP), you must attach it to a private IP address — and it’s one-to-one.”
That means:
1 Elastic IP can only be linked to 1 Private IP at a time.
You can’t have one Elastic IP shared by multiple Private IPs directly.
So traffic knows exactly where to go — no confusion.
Makes it easier to move your Elastic IP to another server if the first one breaks.
Private IP = Your secret house number inside the playground 🏠. Elastic IP = The public phone number for calling you 📞. Rule = 1 phone number belongs to 1 house number — no sharing.
NAT stands for Network Address Translation
NAT Instance = An EC2 server configured to allow outbound internet access for private subnets, but block inbound traffic from the internet.
Private EC2 → NAT Instance → Internet ✅
Internet → NAT Instance → Private EC2 ❌
Key points:
Used when private instances need to download stuff but stay hidden from the public internet.
AWS now recommends NAT Gateways (a managed service) instead of NAT instances, but NAT instances are cheaper and customizable.
Last updated