Tech Matchups: Internet Gateway vs NAT Gateway
Overview
Internet Gateway (IGW) enables direct public internet access for resources in public subnets, allowing inbound and outbound traffic.
NAT Gateway allows private subnet instances to initiate outbound internet traffic while blocking inbound connections.
Both connect VPCs to the internet: IGW for public access, NAT Gateway for private outbound.
Section 1 - Functionality and Traffic Flow
IGW attaches to a VPC, enabling bidirectional traffic for public subnets—e.g., an EC2 web server (10.0.0.10) serves HTTP to 0.0.0.0/0. Requires a public IP or Elastic IP.
NAT Gateway resides in a public subnet, forwarding outbound traffic from private subnets—e.g., an EC2 app server (10.0.1.10) fetches updates. Blocks inbound traffic.
Scenario: IGW exposes a web server to users; NAT Gateway lets a private DB server download patches.
Section 2 - Security and Access Control
IGW requires Security Groups and NACLs to secure public resources—e.g., allowing TCP 80 inbound. Public exposure demands tight rules.
NAT Gateway inherently blocks inbound traffic, needing no inbound rules. Outbound traffic is controlled via Security Groups—e.g., allow TCP 443 to 0.0.0.0/0.
Scenario: IGW needs rules for HTTP access; NAT Gateway auto-protects private instances. IGW is open; NAT Gateway is shielded.
Section 3 - Cost and Scalability
IGW is free, with costs tied to data transfer—e.g., $0.09/GB outbound in us-east-1. Example: 1TB/month outbound costs $92.16.
NAT Gateway charges hourly ($0.045 in us-east-1) plus data processing ($0.045/GB). Example: 1TB/month costs ~$136.80 ($32.40 hourly + $104.40 data).
IGW scales automatically; NAT Gateway scales to 45 Gbps, with multiple NATs for higher throughput.
Scenario: IGW is cheaper for public traffic; NAT Gateway adds cost for private outbound.
Section 4 - Use Case Scenarios
IGW suits public-facing apps—e.g., web servers or API endpoints in public subnets serving global users.
NAT Gateway fits private apps—e.g., backend servers or databases needing internet access for updates without public exposure.
Scenario: IGW for a public e-commerce site; NAT Gateway for a private payment processor.
Section 5 - Comparison Table
| Aspect | Internet Gateway | NAT Gateway |
|---|---|---|
| Traffic | Bidirectional | Outbound Only |
| Subnet | Public | Private via Public |
| Security | SGs/NACLs | Inbound Blocked |
| Cost | Data Only | Hourly + Data |
| Best For | Public Apps | Private Apps |
IGW for public access, NAT Gateway for private outbound. Combine for secure VPC designs.
Conclusion
Internet Gateway and NAT Gateway enable internet connectivity in VPCs with distinct roles. IGW supports public-facing resources with bidirectional access, ideal for web servers. NAT Gateway ensures private resources access the internet securely, perfect for backend services.
Weigh traffic needs (public vs. private), security (open vs. blocked), and cost (data vs. hourly). Use IGW for public subnets, NAT Gateway for private—or combine: IGW for user-facing apps, NAT Gateway for internal services.