I’ve created an RDS Oracle instance and I want to connect to it from an EC2 instance. I created both in the same VPC.
By default, even though they’re in the same VPC, the EC2 will not be able to connect to the Oracle instance because you still need to configure the Security Group to allow inbound traffic.
Let’s summarize the setup like this – both are in VPC1:
EC2 : Security Group SG-111
RDS Oracle instance: Security Group SG-222
Edit SG-222 for the Oracle instance, and add an inbound rule. Instead of adding a CIDR block range, start typing SG-111… and it will list matching SGs with that id – click to select the id for Security Group associated to the EC2. You’ve now allowed inbound traffic to your RDS Oracle instance from the EC2.