Troubleshooting WebSocket Connection Issues in Azure App Service

Question

Hello,

I am having trouble with my Azure App Service application that uses the socket.io library on the backend (Node.js) and the socket.io-client library on the frontend (React). The frontend is hosted on an Azure Static Web App, while the backend is deployed on an App Service. I am receiving the error message "WebSocket is closed before the connection is established".

I am using the following App Service configuration:

• App Service Plan: P2v3
• Runtime Stack: Node - 16-lts
• Region: West Europe

Is there a specific security setting within Azure that I need to adjust to ensure stable WebSocket connections? Also, does Linux App Service support WebSocket?

Thank you for any help you can provide.

Best regards,

Umair

Answer 1

Hello,

Azure App Service supports WebSocket connections for both Windows and Linux. To ensure stable WebSocket connections, consider the following checks:

WebSockets Enabled: Navigate to your App Service in the Azure portal, and under the 'Configuration' section, check the 'General settings' tab to ensure the 'Web sockets' option is enabled.

Always On: In the same tab, make sure the 'Always On' setting is activated to keep your app loaded at all times, which is crucial for maintaining long-lived WebSocket connections.

ARR Affinity: Disable 'ARR Affinity' in the 'General settings' tab if your application depends on a stateful connection to a particular instance, as this setting may route clients to the same instance, potentially disrupting WebSocket connections.

Client and Server Versions: Verify that the versions of socket.io and socket.io-client are consistent across your frontend and backend to avoid compatibility issues.

Upgrade Headers: Confirm that your application properly manages the HTTP Upgrade headers necessary for initiating a WebSocket connection.

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