I am trying to connect to RDS Database from an AWS Lambda (Java).
Which IP should I enable from the RDS Security group rules?
You can't enable this via IP. First you will need to enable VPC access for the Lambda function, during which you will assign it a Security Group. Then, within the Security Group assigned to the RDS instance you will enable access for the Security Group assigned to the Lambda function.
You can configure Lambda to access your RDS instance.
You can enable this using Lambda management console. Select Lambda function which need access to RDS instance and then go to Configuration -> Advanced settings and select the VPC (which is your RDS instance is in) you need it to access.
find out more here http://docs.aws.amazon.com/lambda/latest/dg/vpc.html
来源：https://stackoverflow.com/questions/37030704/allow-aws-lambda-to-access-rds-database