Server connection problem on a blazor site

This error is from Blazor server. the client code uses signal/r (a persistent connection) to talk to the server. The error means the signal/r connection was broken and the client code needs to reconnect. This could caused by either be a server recycle or crash, or unreliable internet connection (say mobile). Check your server logs.

another cause is if the tab hosting the blazor app is not the active tab for a period of time, then the browser will kill the connection.

Hi @Saeed Pooladzadeh,

This may happen after a period of inactivity for your application, it will show the message "Attempting to reconnect to server...".

If you are using blazor 7, 8 or previous version, I suggest you could consider upgrading the version to the 9.

According to this article, you could find:

• When the user navigates back to an app with a disconnected circuit, reconnection is attempted immediately rather than waiting for the duration of the next reconnect interval. This improves the user experience when navigating to an app in a browser tab that has gone to sleep.
• When a reconnection attempt reaches the server but the server has already released the circuit, a page refresh occurs automatically. This prevents the user from having to manually refresh the page if it's likely going to result in a successful reconnection.

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Best Regards,

Brando

Hi, in Blazor Server, the error "Attempting to connect to the server..." means the SignalR connection was lost between the client and server.

Here’s a clear checklist to fix or reduce this issue:

1. Enable WebSockets (required for SignalR)

On IIS or Azure App Service:

• IIS: Install the WebSocket Protocol feature via Server Manager.
• Azure App Service: In the Azure Portal, go to your App Service → Configuration → General Settings → Enable Web sockets.

If behind a reverse proxy (e.g., Nginx or Apache): You must forward WebSocket headers:

For Nginx:

location /_blazor {
    proxy_pass         http://localhost:5000;
    proxy_http_version 1.1;
    proxy_set_header   Upgrade $http_upgrade;
    proxy_set_header   Connection "Upgrade";
}

2. Prevent Idle Timeout (especially on Azure)

Azure App Service will unload your app after idle time by default.

Fix:

• In the Azure Portal, go to your App Service → Configuration → turn on Always On.

3. Handle Reconnect Attempts (in Blazor Server)

You can make Blazor attempt automatic reconnection. Create a JavaScript snippet to override the default SignalR behavior:

Add to _Host.cshtml (before </body>):

<script src="_framework/blazor.server.js" autostart="false"></script>
<script>
    Blazor.start({
        reconnectionOptions: {
            maxRetries: 10,
            retryInterval: 3000
        }
    });
</script>

4. Increase KeepAliveInterval and Timeout Settings

In Program.cs:

builder.Services.AddServerSideBlazor()
    .AddHubOptions(options =>
    {
        options.ClientTimeoutInterval = TimeSpan.FromSeconds(60);
        options.KeepAliveInterval = TimeSpan.FromSeconds(15);
    });

5. Avoid Blocking Calls

Don’t use Thread.Sleep or heavy synchronous work in components — it can block SignalR pings.

Use async/await and background services for long tasks.

6. Inspect Logs for Disconnects

Enable detailed logging to see disconnection causes:

"Logging": {
  "LogLevel": {
    "Default": "Information",
    "Microsoft.AspNetCore.SignalR": "Debug",
    "Microsoft.AspNetCore.Http.Connections": "Debug"
  }
}

7. Network Stability on Client Side

Sometimes the issue is the user’s browser or Wi-Fi dropping packets.

You can handle this more gracefully by showing a custom UI when disconnected (Blazor provides OnConnectionUp, OnConnectionDown events with JavaScript interop).

Hope this helps.