Port 6666 is used by Azure Databricks for secure cluster connectivity, specifically for the secure cluster connectivity relay. This port is primarily utilized in private link scenarios.

Here’s what you need to know about port 6666 in Azure Databricks:

Private Link:

• Purpose: If your Azure Databricks workspace is configured to use Azure Private Link for enhanced security and network isolation, port 6666 is essential for establishing secure connections between your virtual network and the Databricks control plane.
• Firewall Configuration: When using Private Link, ensure that port 6666 is open in your network security group (NSG) or firewall rules to allow outbound traffic from your private endpoint subnet. Additionally, this port needs to be open for inbound traffic on the private endpoint subnet’s NSG.

Standard Deployment (No Private Link):

• Relevance: If you are not using Azure Private Link for your Databricks workspace, port 6666 is not typically required.

Additional Considerations:

• Documentation: Microsoft’s official documentation on Azure Databricks provides detailed instructions on configuring Private Link and the necessary network settings.