Accessing s3 from a Lambda within a vpc

Based on the information you've provided, it seems you're encountering an issue with a Lambda function that's triggered by S3 events but is unable to access DynamoDB or S3 within your VPC. Here are some potential causes and solutions to consider:

1. VPC Configuration: Even though you have S3 and DynamoDB endpoints within your VPC, Lambda functions in a VPC use private IP addresses and cannot directly access the internet. This means they can't use the standard public endpoints for AWS services.

2. Timeout Issues: The lack of logs and the halting behavior suggest that your Lambda function might be timing out. By default, Lambda functions have a 3-second timeout. You may need to increase this timeout in your Lambda configuration.

3. Security Groups: Ensure that the security groups associated with your Lambda function allow outbound traffic to the VPC endpoints for S3 and DynamoDB.

4. IAM Permissions: Double-check that the IAM role associated with your Lambda function has the necessary permissions to access S3 and DynamoDB.

5. VPC Endpoints: Verify that you're using the correct type of VPC endpoint. For S3, you should use a gateway VPC endpoint, while for DynamoDB, you need an interface VPC endpoint.

6. Cross-Region Access: If your Lambda function is trying to access S3 or DynamoDB in a different region from where it's deployed, you may need to set up additional configurations.

To troubleshoot further:

1. Enable VPC flow logs to monitor the network traffic and identify any connectivity issues.

2. Increase the Lambda function's timeout and memory allocation to rule out resource constraints.

3. Test your Lambda function outside the VPC to isolate whether the issue is VPC-related.

4. Use AWS X-Ray to trace requests and identify where the function is getting stuck.

5. Review your Lambda function's code to ensure it's correctly handling errors and not silently failing.

If the issue persists after these checks, you may need to review your VPC architecture or consider using a NAT Gateway to allow your Lambda function to access the internet and AWS services through their public endpoints.

Sources
Cannot access S3 from lambda using boto3 | AWS re:Post
Error TIMEOUT in lambda | AWS re:Post
Cross-regional S3 access from Lambda | AWS re:Post