AWS Lambda now provides IAM condition keys for VPC settings
You can now govern the virtual private cloud (VPC) settings for your Lambda functions using IAM condition keys. Using these condition keys, you can enforce that users only deploy functions that are connected to a VPC. VPC-enabled functions send all traffic through your VPC and abide by your VPC’s network controls. You can use these network controls to define where your functions can connect. You can also restrict access to network locations, including the public internet.
Source:: Amazon AWS