Linux Azure Web App（B1计划）中Blazor Server WebSockets传输启动失败问题求助

Hey there, let's dig into this WebSocket issue you're facing with your B1 Linux Azure Web App. Since your B2 production instance works perfectly with the same code and setup, the problem is likely tied to the B1 plan's limitations or some subtle environment differences. Here are some targeted troubleshooting steps to try:

1. Check B1 Plan's Connection Limits #

Azure App Service B1 tier has lower concurrent connection caps compared to B2. Even with identical code, the B1 might be hitting WebSocket connection limits that the B2 handles easily.

• Head to your Web App in the Azure Portal → Metrics → Add a metric for "WebSocket Connections" to monitor if it's spiking near the B1 limit (B1 allows up to 300 concurrent WebSocket connections by default).

2. Double-Check WebSocket & Network Configurations #

Even if you confirmed settings earlier, it's worth verifying these details:

• Go to Web App → Configuration → General settings → Ensure "Web sockets" is set to On.
• Check for IP restrictions or firewall rules (inbound/outbound) that might block WebSocket traffic. B1 instances sometimes have different default network policies if deployed in a separate VNET/subnet.

3. Validate SSL/TLS Compatibility #

Your custom domain has a valid cert, but mismatched TLS settings can break WebSocket handshakes:

• Go to Web App → TLS/SSL settings → Confirm the "Minimum TLS version" matches your B2 production app (TLS 1.2 or 1.3 is recommended).
• Ensure your SSL binding uses SNI SSL (required for custom domains on Linux App Service).

4. Get Detailed Application Logs #

The generic error message doesn't tell the whole story. Enable verbose logging to uncover more details:

• Go to Web App → App Service logs → Turn on "Application logging (Filesystem)" and set the level to Verbose.
• Reproduce the error, then check logs via Log Stream or in the /home/LogFiles directory. Look for specific issues like handshake failures, port conflicts, or dependency errors.

5. Test WebSocket Connectivity Directly #

Use a tool like wscat to test the connection from your local machine:

wscat -c wss://your-custom-domain.com/your-websocket-endpoint

Compare the output with the same test on your B2 app. Note any error codes (e.g., 403, 502) which can point to authentication or proxy issues.

6. Verify Runtime Stack Consistency #

Even with identical code, the underlying runtime version might differ between plans:

• Go to Web App → Configuration → General settings → Confirm the "Runtime stack" and "Version" match exactly with your B2 production instance.

7. Restart & Clear Cache #

Transient issues can sometimes block WebSocket functionality:

• Restart your B1 Web App directly from the Azure Portal.
• Clear the site cache via Kudu: Go to Web App → Advanced tools → Kudu → Debug console → Bash, then run (adjust path for your runtime):

rm -rf /home/site/wwwroot/node_modules/.cache

If none of these steps resolve the issue, opening a support ticket with Azure might help—there could be plan-specific backend infrastructure issues that aren't visible in the portal.

内容的提问来源于stack exchange，提问作者OrcusZ