How to Fix AWS DMS Connection Endpoint Errors

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If you’re experiencing a connection failure between your AWS Data Migration Service (DMS) and your Redshift serverless, especially with messages like “Test connection failed” along with network errors, don’t worry. Here’s a simple step-by-step guide to help you troubleshoot and fix this problem.

First, understand that your DMS is set up in one Virtual Private Cloud (VPC), while your Redshift serverless is in another VPC. A private link has been created between these two VPCs. However, note that availability zones (AZs) are not supported through this private link, particularly AZ A, which was not included in the setup.

The error message indicates that the network connection isn’t going through properly. This often happens when security groups, route tables, or VPC endpoints aren’t configured correctly.

Start by checking these key points:

Security Groups: Ensure that the security groups for both the DMS replication instance and the Redshift serverless allow inbound and outbound traffic on the required ports. Typically, for Redshift, port 5439 should be open.
VPC Endpoints and Private Link: Since the private link doesn’t support AZ A, verify that your Private Link connection is correctly set up to use the AZs available. Make sure the endpoint is associated with the correct AZs that support this connection.
Routing Tables: Confirm that the routing tables in both VPCs correctly route traffic through the private link. You might need to add or modify route rules to ensure that network traffic flows seamlessly between the VPCs.
Network Access: Check if any network ACLs (Access Control Lists) are blocking traffic. They should allow communication over the necessary ports and protocols.
Redshift and DMS Configuration: Ensure that both the source and target endpoints are correctly configured in AWS DMS, with valid endpoint URLs and credentials.

If everything seems correct but you’re still facing issues, try creating a new VPC endpoint in a supported AZ or adjust the existing private link to cover the necessary AZs. Also, double-check that all relevant security policies and permissions are in place.

Once these configurations are verified and corrected, rerun the test connection. This should resolve the network error and allow your replication process to start smoothly.

Remember, network configurations between VPCs can be tricky, but paying close attention to security groups, route tables, and endpoint setups usually fixes the issue. Take your time to review each setting, and you’ll get your data replication back on track.