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Difficulty: MediumDebugging Lambda Execution and Configuration Issues

A serverless order processing application utilizes an AWS Lambda function to send confirmation emails via a third-party API. The function is also configured to access an Amazon Aurora PostgreSQL database in a private subnet. The developer has configured the Lambda function to run inside the private subnets of the VPC to enable database access.

During testing, the developer observes two issues:
1. The Lambda function fails to connect to the third-party email API.
2. The database connection pool is frequently exhausted, and Lambda execution logs show connection timeouts during concurrent invocations.

Which two actions should the developer take to resolve these issues?

  1. Initialize the database connection client outside the Lambda handler function to enable connection reuse across invocations.Answer
  2. Provision a NAT Gateway in a public subnet, and configure the route table of the Lambda private subnets to route outbound internet traffic through the NAT Gateway.Answer
  3. C
    Move the Lambda function configuration to public subnets within the VPC to enable direct internet access.
  4. D
    Implement logic within the handler function to terminate the database connection pool at the end of each execution, and extend the Lambda function's timeout configuration.
  5. E
    Create a VPC gateway endpoint for the third-party email API and associate it with the route tables of the Lambda subnets.

Answer

To resolve the issues, the developer must initialize the database connection client outside the Lambda handler function to enable connection reuse, and provision a NAT Gateway in a public subnet to route outbound internet traffic from the private subnets.
The correct solution involves reusing database connections by instantiating the client outside the handler, and establishing internet connectivity for the private subnet using a NAT Gateway.

Step-by-Step Solution

1
Analyze the connectivity failure to the third-party email API.
Recognize that because the Lambda function is placed in a private subnet within a VPC to access Aurora, it lacks access to the public internet by default.
VPC-associated Lambda functions require a NAT Gateway or NAT Instance in a public subnet, with appropriate route tables, to establish outbound connections to external endpoints.
2
Diagnose the database connection pool exhaustion.
Identify that the database client initialization code is situated inside the handler function.
Placing the connection logic inside the handler function forces Lambda to create a new database connection on every single invocation, rapidly depleting the database's available connections. Placing it outside the handler allows subsequent invocations in the same execution environment to reuse the connection.
3
Apply the VPC routing and code updates.
Create the NAT Gateway in a public subnet, add a route in the private subnet route table pointing `0.0.0.0/0` traffic to the NAT Gateway, and refactor the Lambda code to instantiate the database client during the initialization phase.
This combined approach resolves both the internet egress restriction and the connection leak under load.

Key Concept

Troubleshooting VPC egress routing for Lambda functions and optimizing resource utilization through execution context reuse.
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Topics

Debugging Lambda Execution and Configuration Issues

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