Port 8443 is one of the additional ports that Azure Databricks is opening for communication between your workspace and its control plane. This change was announced in early 2024, and you likely received a notification about it.

Key points to note:

• Purpose: The additional ports (including 8443) enhance connectivity and communication between your Databricks workspace and Azure Databricks’ backend services.
• Action Required: For most users, Azure Databricks automatically updated the necessary Network Security Groups (NSGs) to allow traffic on these new ports. However, if you manage your own NSGs, you might need to manually update them to include port 8443 (and the others in the range 8443-8451).
• Deadline: The deadline to open these ports was January 31, 2024. If you haven’t already, you should update your NSGs as soon as possible.