A developer is building a new serverless application using AWS Lambda functions. This application needs to securely interact with a third-party API that requires a static egress IP address for whitelisting purposes. How can the developer ensure that the Lambda functions always use a static egress IP address?
- AConfigure the Lambda function within a VPC, route its traffic through a NAT Gateway, and associate an Elastic IP address with the NAT Gateway.
- BConfigure the Lambda function within a VPC and attach an Elastic IP address to the Lambda function.
- CUse AWS Global Accelerator to provide a static IP address for the Lambda function's egress traffic.
- DDeploy a dedicated EC2 instance with a static IP address and route all Lambda traffic through this instance using a VPC endpoint.
Show answer & explanationAnswer & explanation
Correct answer: A. Configure the Lambda function within a VPC, route its traffic through a NAT Gateway, and associate an Elastic IP address with the NAT Gateway.
To provide a static egress IP for Lambda functions that interact with resources outside of AWS (like a third-party API requiring whitelisting), the Lambda function must be configured within a VPC. The outbound traffic from the Lambda function should then be routed through a NAT Gateway, which can be associated with an Elastic IP address. This Elastic IP address will serve as the static egress IP.
Why the other options are wrong
- B. Lambda functions cannot directly have an Elastic IP address attached to them. They run within an AWS-managed VPC or a customer-configured VPC.
- C. AWS Global Accelerator provides static IP addresses that act as fixed entry points to your applications, improving performance and availability. It does not, however, provide static egress IP addresses for Lambda functions accessing external services.
- D. While technically possible, routing all Lambda traffic through a dedicated EC2 instance is overly complex, less scalable, and introduces a single point of failure and higher operational overhead compared to using a NAT Gateway.
Lambda Static Egress IP
To provide AWS Lambda functions with a static public IP address for outbound traffic, they must be configured within a VPC and route their internet-bound traffic through a NAT Gateway associated with an Elastic IP.
- Lambda functions are serverless and typically don't have static egress IPs by default.
- VPC configuration is required to control Lambda's network access.
- NAT Gateway with an Elastic IP is the standard solution for static egress IPs.
Memory trick: Lambda's traffic needs a 'NAT'ural 'EIP' exit strategy.