What Should I Do If an ECS Cannot Connect to an RDS DB Instance Through a Private Network?

Perform the following steps to identify the problem:

1. Check whether the ECS and RDS DB instances are located in the same VPC.
   • If they are in the same VPC, go to 2.
   • If they are in different VPCs, create an ECS in the VPC in which the RDS DB instance is located.

2. Check whether a security group has been added to the ECS.
   • If a security group has been added, check whether the rules are configured correctly.

     For MySQL DB instances, see the security group description in Step 1: Create a DB Instance. Then, go to 3.

     For PostgreSQL DB instances, see the security group description in Step 1: Create a DB Instance. Then, go to 3.

     For Microsoft SQL Server DB instances, see the security group description in Step 1: Create a DB Instance. Then, go to 3.

   • If no security group has been added, go to the VPC console from the ECS details page and click Security Groups to add a security group.

3. On the ECS, check whether the RDS DB instance port can be connected.

   The default port of RDS for MySQL is 3306.

   The default port of RDS for PostgreSQL is 5432.

   The default RDS for Microsoft SQL Server port number is 1433.

   telnet <IP address> {port number}

   • If the ECS can connect to the RDS DB instance port, the network between the ECS and the RDS DB instance is normal and no further action is required.
   • If the ECS still cannot connect to the port, contact technical support.