App Service to Azure MySQL (Private Endpoint) Connection Timeout

Hello @Pavol Karkas,

Welcome to Microsoft Q&A Platform. Thank you for reaching out & hope you are doing well.

I understand your question about the Azure App Service failing to establish a TCP connection to the Azure Database for MySQL Flexible Server over an existing approved Private Endpoint connection, where the application consistently throws a Connection timed out (mysqli_sql_exception) error.

It looks like the problem is with the private connection setup rather than your database or login details, since you can connect over the public internet just fine.

Sometimes after restarting your app and database, the private network settings or DNS (which helps your app find the database) can get mixed up. To fix this, please check these things:

1. From your app service, run a DNS lookup for your database's name. It should point to the private IP address. If it points to the public IP, then the private DNS settings might need to be reconnected.
2. Make sure the private DNS zone (privatelink.mysql.database.azure.com) is properly linked to the virtual network your app uses.
3. Confirm your app is still connected to the right virtual network and subnet.
4. Check in the Azure portal that the private endpoint is still showing as Approved and Connected.
5. Verify your app is connecting using the full database name (like yourserver.mysql.database.azure.com) rather than a direct IP address.

Looks like turning off secure transport only helped on the public connection, so SSL isn’t the reason for the timeout. The real issue seems to be that your app’s traffic isn’t making it to the database over the private link.

Next, please check the DNS lookup first. If it shows the public IP, try relinking the private DNS zone to your network. If it shows the private IP but still times out, double-check the private endpoint status.

Reference:
https://learn.microsoft.com/en-us/azure/mysql/flexible-server/how-to-troubleshoot-common-connection-issues
https://learn.microsoft.com/en-us/azure/mysql/flexible-server/concepts-networking-private-link

Kindly let us know if the above helps or you need further assistance on this issue.

Please "Accept the Answer" if the information helped you. This will help us and others in the community as well.

It sounds like you are experiencing a connectivity issue with your Azure App Service when trying to connect to your Azure Database for MySQL Flexible Server over a Private Endpoint. Since you mentioned that you can connect via a public IP but not through the private link, here are some steps to troubleshoot the issue:

1. Private Endpoint Configuration: Ensure that the Private Endpoint is correctly configured and that its connection state is Approved. You can check this in the Azure portal under the Private Link Center.
2. Network Configuration: Verify that the virtual network where your App Service is deployed has proper connectivity to the virtual network hosting the Private Endpoint. Ensure that the App Service is in the same VNet or has VNet integration configured correctly.
3. DNS Resolution: Check that the DNS settings for your App Service are resolving to the private IP address of the Private Endpoint. Incorrect DNS settings can lead to connection timeouts.
4. Firewall Rules: Although you mentioned that the public firewall is open, ensure that the firewall settings for the Azure Database for MySQL are configured to allow connections from the private IP addresses of your App Service.
5. Network Security Groups (NSGs): Double-check any NSGs associated with the subnet where the Private Endpoint resides to ensure they are not blocking traffic.
6. Testing Connectivity: Use tools like Azure Network Watcher to test the connection from your App Service to the Private Endpoint. This can help identify if there are any routing issues.
7. Logs and Monitoring: Review logs in Azure Monitor to see if there are any indications of failed connection attempts or other errors that could provide more context about the timeout.

By following these steps, you should be able to identify and resolve the connectivity issue between your Azure App Service and the Azure Database for MySQL Flexible Server over the Private Endpoint.