Concepts
One important aspect is understanding how to enable instances in a private subnet to connect to the internet or other AWS services without receiving inbound traffic from the internet. This is where NAT (Network Address Translation) devices come into play, and AWS offers two options: NAT instances and NAT gateways.
What is a NAT Instance?
A NAT instance is an Amazon EC2 instance that is configured to forward traffic from private instances to the internet or other AWS services. Since it is an EC2 instance, it gives you the flexibility to configure it as much as you would any EC2 instance, and you are responsible for its management, scaling, and patching.
What is a NAT Gateway?
A NAT Gateway is a managed NAT service provided by AWS that allows instances in a private subnet to connect to the internet or other AWS services. It is a highly available and managed service, meaning AWS is responsible for its maintenance and high availability.
Cost Comparison: NAT Instance vs. NAT Gateway
NAT Instance Costs:
- EC2 Instance Costs: You pay for the EC2 instance used as a NAT instance according to the respective instance size pricing.
- Data Processing Costs: There are no additional costs for the data processed by the NAT instance.
- Bandwidth Costs: Standard EC2 bandwidth costs apply.
NAT Gateway Costs:
- Hourly Charge: You pay an hourly charge for the NAT Gateway itself, regardless of the data processed.
- Data Processing Costs: You also pay for the data processed (per GB) through the NAT Gateway.
- Bandwidth Costs: Standard AWS data transfer costs for the region apply.
Here is a simplified comparison table for a better understanding:
| Cost Factor | NAT Instance | NAT Gateway |
| Instance/Hourly Cost | Based on EC2 instance type and pricing | Fixed hourly rate depending on AWS region |
| Data Processing | Free | Charged per GB processed |
| Bandwidth | Standard EC2 data transfer rates apply | Standard AWS data transfer rates apply |
| Additional Maintenance | Manual patching, scaling, and management | Managed by AWS; no additional effort required |
Performance and Functionality Considerations:
NAT gateways are built to be highly available and automatically scale up to 45 Gbps of bandwidth. They do not require any administrative maintenance as AWS handles patching, updates, and high availability. In contrast, NAT instances’ performance is tied to the size of the EC2 instance, and you must handle scaling (by changing instance sizes) and high availability (by implementing failover mechanisms) manually.
Example Use Cases:
- Small Scale Operations: For environments where cost-savings are imperative, a t3.micro NAT instance might be more cost-effective than a NAT gateway.
- Large Scale, Enterprise Grade: For large-scale operations requiring consistent performance and high availability without administrative overhead, a NAT Gateway would be the preferred choice.
Best Practices:
- When using a NAT instance, ensure that you configure Source/Destination Check to be disabled, as NAT requires handling traffic that is not explicitly destined for the NAT instance itself.
- For NAT gateways, it is recommended to create one NAT gateway per Availability Zone for fault tolerance purposes.
- Monitor your cost and traffic patterns regularly to optimize resources. For instance, if a NAT instance is underutilized, consider downsizing or switching to a NAT gateway.
Conclusion:
Choosing between a NAT instance and a NAT gateway largely depends on the specific requirements of the architecture in terms of cost, performance, scale, and administrative overhead. AWS Certified Solutions Architect – Associate candidates should understand both options, their cost structures, and appropriate use cases to make informed decisions when architecting solutions on AWS.
Answer the Questions in Comment Section
True or False: NAT gateways have a higher bandwidth limit compared to NAT instances.
- (A) True
- (B) False
Answer: A
Explanation: True, NAT gateways are designed to handle higher bandwidth limits compared to NAT instances, providing greater throughput.
What is the cost of a NAT gateway charged by?
- (A) Number of instances behind it
- (B) Hourly rate
- (C) Data transfer volume
- (D) Fixed monthly fee
Answer: B, C
Explanation: NAT gateways are charged based on an hourly rate for provisioned gateways and the amount of data processed.
True or False: You can enable AWS Shield (a managed Distributed Denial of Service – DDoS – protection service) on a NAT instance but not on a NAT gateway.
- (A) True
- (B) False
Answer: B
Explanation: False, AWS Shield Standard is automatically included to protect both NAT instances and NAT gateways at no additional cost.
Which of the following statements best describe a NAT instance?
- (A) It doesn’t require manual intervention for high availability.
- (B) It can be used as a bastion server.
- (C) It scales automatically based on traffic.
- (D) It supports burstable performance.
Answer: B
Explanation: A NAT instance can be used as a bastion server allowing SSH or RDP access to instances in private subnets, but it does not scale automatically, nor does it provide built-in high availability.
Which AWS service is responsible for scaling up the bandwidth automatically to meet demand?
- (A) NAT Gateway
- (B) NAT Instance
Answer: A
Explanation: NAT Gateway automatically scales the bandwidth up or down based on the demand, while a NAT instance requires manual scaling.
True or False: NAT gateways require security groups to control inbound or outbound traffic.
- (A) True
- (B) False
Answer: B
Explanation: False, NAT gateways are fully managed by AWS and they do not require nor support security groups, whereas NAT instances require security groups to control traffic.
Which of the following can be a deciding factor when choosing between a NAT gateway or a NAT instance?
- (A) The ability to support burstable traffic
- (B) The need for high availability without manual intervention
- (C) The requirement for custom packet inspection
- (D) The cost of the solution
Answer: B, C, D
Explanation: High availability without manual intervention, the need for custom packet inspection (possible with NAT instances), and the overall cost implications are key factors in deciding between using NAT gateways and NAT instances.
True or False: NAT instances are automatically assigned a public IP address by AWS.
- (A) True
- (B) False
Answer: B
Explanation: False, while NAT instances do require a public IP to function correctly, it is not automatically assigned by AWS; you need to manually allocate and associate an Elastic IP (EIP) with the NAT instance.
When comparing NAT gateways to NAT instances, which one by default offers redundancy and failover?
- (A) NAT Gateway
- (B) NAT Instance
Answer: A
Explanation: NAT Gateways offer built-in redundancy and failover capabilities by default while NAT instances require additional configuration for achieving high availability.
True or False: There are no data processing or hourly costs associated with a NAT instance.
- (A) True
- (B) False
Answer: B
Explanation: False, while a NAT instance doesn’t have specific “NAT” costs, you still incur costs based on the instance type and size, data transfer, and associated EIP charges, if any.
For a NAT gateway to function, it must be created in:
- (A) A public subnet with an Internet Gateway
- (B) A public subnet with a Virtual Private Gateway
- (C) A private subnet with a NAT instance
- (D) A private subnet with an Internet Gateway
Answer: A
Explanation: A NAT gateway must be created in a public subnet with an Internet Gateway to enable instances in the private subnet to connect to the internet without receiving inbound traffic from the internet.
True or False: AWS Managed NAT gateways support assigning Elastic IP (EIP) addresses directly to managed instances.
- (A) True
- (B) False
Answer: B
Explanation: False, AWS Managed NAT gateways allow instances in the private subnet to initiate outbound traffic to the internet or other AWS services using the NAT gateway’s Elastic IP address, but you cannot assign EIPs directly to the instances using NAT gateways.
Great post! The comparison between NAT instances and NAT gateways was very helpful.
Glad I found this blog. I’m preparing for the SAA-C03 exam and this topic is crucial.
From a cost perspective, NAT gateways can be more expensive than using NAT instances, especially for low traffic applications.
Thanks for the informative article!
I prefer NAT gateways for their high availability and scalability, even though they might cost a bit more.
How significant are the performance differences between NAT instances and NAT gateways?
Appreciate the breakdown!
For exam prep, would it be more important to understand the technical specifics or the cost implications?