My ECS tasks (VPC A) can't connect to my RDS (VPC B) even though the VPCs are peered and networking is configured correctly

Hi, As mentioned in the question, my ECS tasks cannot connect to my RDS. The ECS tasks try to resolve the rds by name, and it resolves to the RDS public IP (RDS has public and private IPs). However, the security group on RDS doesn't allow open access from all IPs so the connection fails. I temporarily allowed all connections and could see that the ECS tasks are routing through the open internet to access the RDS.

Reachability Analyzer checking specific tasks' Elastic Network Interface to the RDI ENI is successful, using internal routing through the peering connection.

At the same time I have another server on VPC C that can connect to the RDS. All the config is similar between these two apps, including the peering connection, security group policies and routing tables. Any help is appreciated

Here are some details about the VPCs

VPC A - 15.2.0.0/16 [three subnets] VPC B - 111.30.0.0/16 [three subnets] VPC C - 15.0.0.0/16 [three subnets]

Peering Connection 1 between A and B Peering Connection 2 between C and B

Route table for VPC A: 111.30.0.0/16 : Peering Connection 1 15.2.0.0/16: Local 0.0.0.0/0: Internet Gateway

Route table for VPC C: 111.30.0.0/16: Peering Connection 2 15.2.0.0/16: Local 0.0.0.0/0: Internet Gateway

Security groups allow traffic to RDS: Ingress: 15.0.0.0/16: Allow DB Port 15.2.0.0/16: Allow DB Port Egress: 0.0.0.0/0: Allow all ports

When I add the rule: 0.0.0.0/0 Allow DB Port to the RDS, then ECS can connect to my RDS through its public IP.