Possible to run AWS VPC Reachability analyzer from Lambda ENI to RDS endpoint?

Hello,

Yes this can be done using Network Interfaces in the VPC Reachability Analyzer.

Assuming the Lambda is in a VPC, you should be able to locate the ENI from the Network Interfaces page under EC2 > Network & Security > Network Interfaces.

You can grab the ENI of the Lambda as well as the ENI of the RDS Instance and use the Reachability Analyzer to test the connectivity.

Here is additional documentation on configuring a Lambda to access an RDS database in a VPC: https://docs.aws.amazon.com/lambda/latest/dg/services-rds-tutorial.html