VS Code "Failed to connect to the remote extension host server (Error: WebSocket close with status code 1006)" error when connecting to a remote azure ML server

Hi Sarah

Below issue

Failed to connect to the remote extension host server (Error: WebSocket close with status code 1006)
Occurs when accessing Azure ML notebooks in VS Code because of following regions.

• Network restrictions or firewall configurations blocking WebSocket communication.
• Outdated Azure ML extension in VS Code.
• DNS resolution on Storage FQDN is not happening

Check DNS resolution of storage and other FQDN from private endpoint

nslookup <fqdnofhosturlin DNS records> should resolve to private IPs

https://free.blessedness.top/en-us/azure/machine-learning/how-to-troubleshoot-secure-connection-workspace?view=azureml-api-2

Check outbound network settings

• Allow traffic to:
  • *.vscode.dev
  • raw.githubusercontent.com
    These domains are required for VS Code’s WebSocket communication.

Verify Networking configuration

Review Network Security Group (NSG) settings to confirm changes.

• Use Azure Monitor to validate connectivity to the above domains.

Firewall and proxy whitelisting

Please whitelist below VS code URLs

https://free.blessedness.top/en-us/azure/machine-learning/how-to-access-azureml-behind-firewall?view=azureml-api-2&tabs=ipaddress%2Cpublic#hosts

Configure firewall ports

• Ensure ports 8704–8710 are open.
  VS Code server uses these ports dynamically.

Enable WebSocket communications

Confirm your network supports WebSocket connections.

• Reference: https://docs.microsoft.com/azure/machine-learning/how-to-access-azureml-behind-firewall?tabs=ipaddress.

Update Azure AML extension

• Install the latest version of the Azure Machine Learning extension in VS Code.
• If outdated, update or reinstall.

Follow up questions

• Are you on a private network? Any recent firewall changes?
• Can you connect to other services, or is it only Azure ML notebooks?
• Have you tried switching networks (e.g., Wi-Fi → mobile hotspot)?

Reference

• https://free.blessedness.top/azure/machine-learning/how-to-secure-workspace-vnet
• https://docs.microsoft.com/azure/machine-learning/how-to-access-azureml-behind-firewall?tabs=ipaddress
• https://free.blessedness.top/azure/machine-learning/how-to-secure-training-vnet

Thank you.