Q: How to configured Default VPC IN AWS? i want to  send mail using node mailer in NodeJS if my lambda function is developed in default VPC because I have to access RDS too from the lambda function.
I am unable to send success mail for data successfully inserted in RDS if I deployed my lambda function in default VPC WHAT changes I need to do so I can send.
IF I choose NO vpc then I am unable to set data to database.

A: From https://docs.aws.amazon.com/lambda/latest/dg/configuration-vpc.html, 

When you connect a function to a VPC in your account, it does not have access to the internet unless your VPC provides access.

I take this to mean that if you wish to access both RDS and the internet from lambda from within your VPC, you need a NAT gatway (or to spin up your own instance).   In other words, lambda does not support internet access with a public IP through an Internet Gateway, which is the mechanism of internet access within your vpc.  
If you don't mind the cost, about 4.5 cents an hour plus data transfer last I checked, the simplest solution is probably:


*

*add another subnet to your VPC.  

*Add a NAT Gateway to your VPC.

*Add a route table to the subnet that routes through the NAT Gateway

*put your lambda in that subnet


This essentially creates a connection to the internet in that VPC without your lambda holding a Public IP address.  
