Networking
What is NAT Gateway and NAT Instance
First: What’s NAT?
NAT = Network Address Translation. It lets devices in a private network talk to the internet without showing their private IP.
Think of it like:
You (private network) want to send a letter ✉️ to a shop (internet)
But you don’t want the shop to know your home address
So you send it through a post office (NAT) that uses its own address
NAT Gateway
AWS-managed (you don’t manage the server)
Scales automatically
Fast and highly available
Costs more
Can only be used for outbound internet access, not inbound.
It’s like an automatic toll booth — no operator, runs 24/7, fast, but you pay AWS.
NAT Instance
Your EC2 server acting as NAT
You manage updates, patches, scaling
Cheaper but slower & more work
You can customize firewall rules
Can be used for special routing setups
It’s like a manual toll booth with a human operator — cheaper, customizable, but you must maintain it.
What is a VPC?
Think of a VPC as your own private village 🏡 inside AWS. You build roads (network), houses (servers), gates (firewalls), and choose who comes in and out.
Why do we use VPC?
To keep resources secure and organized
To control traffic going in and out
To segment workloads (e.g., frontend, backend, database)
To create private zones and public zones
VPC BASICS:
VPC = Your private network
Like your own mini data center in the cloud
Subnets = Smaller sections inside your VPC
Like districts in your village
You can make:
Public subnet = can talk to internet
Private subnet = hidden from internet
Route Table = Road map
Tells traffic where to go.
Example: “If traffic is going to the internet, use the Internet Gateway.
Internet Gateway (IGW)
Like the main gate to your village
Lets things go to/from internet
NAT Gateway / NAT Instance
Lets private servers go to internet, but not receive traffic back
Like a one-way mirror
Security Groups = Firewalls for servers
Controls who can talk to your EC2
Example: Allow port 22 (SSH) only from your laptop IP
Network ACLs = Firewalls for subnets
Optional, subnet-level rules
Statelss (you must allow both in and out)
DEEPER CONCEPTS:
1. VPC Peering
Connect 2 VPCs (like 2 villages with a private road)
🛫 2. Transit Gateway
Hub-and-spoke model to connect many VPCs & on-premises locations
🌉 3. VPC Endpoints
Connect to AWS services like S3, DynamoDB privately (no internet)
🔒 4. VPC Flow Logs
Logs of who talks to who in your VPC — great for security and audit
🧠 5. IPv6 Support
For internet-scale, newer networking needs
What is Bastion Host?
A bastion host is like the security guard at the gate 🛡️ of your private AWS network.
You connect to it from the internet (using SSH).
Then, from there, you can go inside to talk to your private EC2 servers.
So it’s a jump box — a doorway into your private network.
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