Unable to connect with RDS which is in private subnet and its under nat gateway

hi,
It looks like that you need to make sure mysql 3306 port is opened.
I hope the below knowledge will help you.

How can I connect to a private Amazon RDS DB instance from a local machine using an Amazon EC2 instance as a bastion host? https://repost.aws/knowledge-center/rds-connect-ec2-bastion-host

Also please refer the AWS document.

Can't connect to Amazon RDS DB instance https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/CHAP_Troubleshooting.html#CHAP_Troubleshooting.Connecting

Hi Subha,

your connection error likely stems from security group or NAT Gateway configuration. Here I will provide

Check Security Groups:

1. Ensure the RDS security group allows inbound traffic on port 3306 from your VM's security group ID.
2. Verify your VM's security group allows outbound traffic on port 3306 to the RDS endpoint (not the public DNS).

Verify NAT Gateway:

1. Confirm the private subnet's route table is associated with the NAT Gateway.
2. Make sure the NAT Gateway is launched in a public subnet with internet access.

Test Connectivity:

From your VM, try pinging the NAT Gateway's public IP to ensure network reachability.

refferal link: https://docs.aws.amazon.com/vpc/latest/userguide/vpc-security-groups.html