Internet Gateways and NAT Gateways are essential networking components in Amazon Web Services (AWS) that enable connectivity between your Virtual Private Cloud (VPC) and the internet.
**Internet Gateway (IGW)**
An Internet Gateway is a horizontally scaled, redundant, and highly available VPC comp…Internet Gateways and NAT Gateways are essential networking components in Amazon Web Services (AWS) that enable connectivity between your Virtual Private Cloud (VPC) and the internet.
**Internet Gateway (IGW)**
An Internet Gateway is a horizontally scaled, redundant, and highly available VPC component that allows communication between instances in your VPC and the internet. It serves two primary purposes: providing a target in your VPC route tables for internet-routable traffic and performing network address translation (NAT) for instances with public IPv4 addresses. Internet Gateways support both inbound and outbound traffic, making them ideal for resources that need to be publicly accessible, such as web servers. There is no additional charge for using an Internet Gateway, and it does not impose bandwidth constraints.
**NAT Gateway**
A NAT (Network Address Translation) Gateway enables instances in private subnets to connect to the internet or other AWS services while preventing the internet from initiating connections with those instances. This is crucial for maintaining security while allowing private resources to download updates, patches, or access external APIs. NAT Gateways are managed by AWS, providing automatic scaling and high availability within an Availability Zone. Unlike Internet Gateways, NAT Gateways incur hourly charges and data processing fees.
**Key Differences**
- Internet Gateways allow bidirectional traffic (inbound and outbound), while NAT Gateways only permit outbound traffic initiated from your VPC.
- Resources using Internet Gateways require public IP addresses; NAT Gateway users keep private IP addresses.
- Internet Gateways are free; NAT Gateways have associated costs.
**Use Cases**
Use Internet Gateways for public-facing applications like websites. Use NAT Gateways for private instances that need outbound internet access for software updates or external service communication while remaining inaccessible from the public internet.
Internet Gateways and NAT Gateways: Complete Guide for AWS Cloud Practitioner
Why This Topic Is Important
Understanding Internet Gateways and NAT Gateways is fundamental to AWS networking. These components control how your resources communicate with the internet, which is essential for security, cost management, and architectural design. The AWS Cloud Practitioner exam frequently tests your knowledge of when and why to use each gateway type.
What Is an Internet Gateway?
An Internet Gateway (IGW) is a horizontally scaled, redundant, and highly available VPC component that enables communication between your VPC and the internet. Key characteristics include:
• Bidirectional communication - Allows both inbound and outbound internet traffic • No bandwidth constraints - Scales automatically to handle traffic • Highly available - AWS manages redundancy across Availability Zones • No additional cost - You only pay for data transfer • One per VPC - Each VPC can have only one Internet Gateway attached
What Is a NAT Gateway?
A NAT (Network Address Translation) Gateway enables instances in private subnets to connect to the internet while preventing the internet from initiating connections to those instances. Key characteristics include:
• Outbound only - Allows resources to access the internet but blocks unsolicited inbound connections • Managed service - AWS handles availability and scaling • Hourly charges apply - You pay for provisioning time and data processing • AZ-specific - Created in a specific Availability Zone • Requires an Internet Gateway - The NAT Gateway uses the IGW to reach the internet
How They Work Together
Public Subnet Architecture: Resources in public subnets use the Internet Gateway to send and receive traffic from the internet. The route table points 0.0.0.0/0 to the Internet Gateway.
Private Subnet Architecture: Resources in private subnets route their internet-bound traffic to a NAT Gateway in a public subnet. The NAT Gateway then forwards traffic through the Internet Gateway. This allows private resources to download updates or access external APIs while remaining protected from inbound internet access.
Key Differences Summary
• Internet Gateway: Two-way traffic, used by public subnets, free to use • NAT Gateway: Outbound traffic only, used by private subnets, has hourly and data costs
Exam Tips: Answering Questions on Internet Gateways and NAT Gateways
Tip 1: When a question mentions resources needing to receive traffic from the internet (like a web server), think Internet Gateway and public subnets.
Tip 2: When a question describes resources that need to download updates or patches but should not be accessible from the internet, the answer involves NAT Gateway in a private subnet configuration.
Tip 3: If you see a scenario about database servers or application backends needing internet access for software updates, NAT Gateway is typically the correct choice for maintaining security.
Tip 4: Questions about cost optimization may reference NAT Gateways since they incur charges, unlike Internet Gateways which have no provisioning cost.
Tip 5: Remember that a NAT Gateway depends on an Internet Gateway - it cannot function alone. If a question asks what is needed for private subnet internet access, both components are required.
Tip 6: For high availability scenarios, remember that best practice is to deploy NAT Gateways in multiple Availability Zones to prevent a single point of failure.
Tip 7: Watch for questions about Elastic IP addresses - NAT Gateways require an Elastic IP, while Internet Gateways do not.