amazon web services - Connecting AWS EC2 API to AWS RDS on same VPC, works externally

Question

New to AWS, and I am attempting to connect an API on my EC2 instance with my RDS. Attempts return a 500 Error

What I am able to do successfully:

Connect to the RDS with an API hosted on an external server. Run API's on my EC2 instance, just not ones that connect to database.

What solutions I have attempted: Added new MYSQL/Aurora Inbound and Outbound rules to include: EC2 Private IPv4 Address/32 EC2 Public IPv4/32 EC2 Security Group

Because I can reach the database externally and run PHP scripts on the server, I am leading that the issue is with the EC2 Connecting with the RDS though I am sure it could be something else.

*I am using PHP APIs to connect to MySQL RDS

Thank you for your time and assistance.

Answer 1

If you connect the same way as the external server (maybe via port 3306) then the EC2 should connect via port 3306 too.

If your security group is blocking port 3306 , and you are connecting via the public endpoint, then you may not be able to connect to the database.

I recommend disabling public port 3306 access on the RDS , and only allow "internal" IP address to access the database via port 3306 , that way you can configure the EC2 to access the RDS using the internal IP address.

By internal I mean the LAN IP of the RDS, assuming they are in the same VPC and AZ (cross AZ can be allowed too, just depends on how you set it up).