Why Can\'t My EC2 Instance Connect to My RDS Instance Even After Adding Security Groups?

Troubleshooting Connection Issues between EC2 and RDS Instances

Users often encounter difficulties in establishing connections between EC2 and RDS instances, leading to common error messages like "Can't connect to MySQL server." To address this issue, it's crucial to consider the security settings and firewall configurations of both instances.

In this case, the user has correctly added the EC2 instance's security group to the RDS security group, but the issue persisted. This suggests that the problem may not reside in the access control rules but rather in the inbound rules of the RDS security group.

Resolving the Issue

To resolve this issue, follow these steps:

1. Navigate to the list of RDS instances.
2. Select the target RDS instance and click on the "Security group rules" section.
3. In the "Inbound rules" tab, click on the "Edit" button.
4. Locate the "Source field" in the inbound rule and modify it to include the IP address or IPv4 CIDR block of the EC2 instance. This allows the RDS instance to accept incoming connections from the EC2 instance.
5. Save the changes to the security rule.

By applying these steps, the RDS instance will now allow inbound connections from the specified EC2 instance, resolving the connection issue.

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