Merge pull request rubyonjets#493 from iqre8/patch-1

Update activerecord.md

docs/_docs/database/activerecord.md

@@ -40,6 +40,24 @@ On AWS Lambda, there's something called the [Lambda Execution Context](https://d
 
 It's also worth noting that AWS clients provided by the [Jets::AwsServices](https://github.com/tongueroo/jets/blob/master/lib/jets/aws_services.rb) module similarly leverage the Lambda Execution context. IE: The clients get reused between lambda calls.
 
+## RDS Database Support
+
+When creating a database on AWS RDS, you can select between mySQL and PostgreSQL.
+When you've created an RDS it will create/use a VPC with at 3 subnets.
+
+To use it with Jets you'll need to do several things.
+Create a lambda security group for lambda functions. No Inbound rules.
+Create a cloudformation security group for lambda functions. Inbound rules would be HTTPS from the lambda security group.
+[Create an endpoint](https://docs.aws.amazon.com/vpc/latest/userguide/vpce-interface.html#create-interface-endpoint) to allow the lambda security group to cloud formation.
+Create a security group to allow traffic from the lambda security group to the RDS VPC for the DB Engine. Inbound rules for PGSQL would be from TCP/5432 - Postgresql from the lambda security group.
+
+Add the vpc_config for the lambda functions in config/application.rb:
+
+    config.function.vpc_config = {
+      security_group_ids: %w[ <lambda security group> ],
+      subnet_ids: %w[ <rds subnet 1> <rds subnet 2> <rds subnet 3> ]
+    }
+
 ## Aurora Database Support
 
 Aurora should work since it is MySQL compatible. Note, with Aurora, your Lambda functions must be configured with a VPC.