SignalR Service¶

This recipe covers adding real-time messaging to Azure Functions Node.js v4 with Azure SignalR Service in serverless mode. It uses the SignalRConnectionInfo input binding to implement the required negotiate endpoint and the SignalR output binding to broadcast messages. In the v4 model, SignalR bindings are declared with input.generic and output.generic.

Architecture¶

flowchart TD
    CLIENT[Browser Client] --> NEG[negotiate Function]
    NEG --> INFO[SignalRConnectionInfo Input]
    INFO --> SR[(Azure SignalR Service)]
    CLIENT -->|WebSocket| SR
    PUB[broadcast Function] --> OUT[SignalR Output]
    OUT --> SR
    SR -->|push| CLIENT

Prerequisites¶

SignalR Service bindings are included in the default extension bundle. Ensure your host.json references it:

{
  "version": "2.0",
  "extensionBundle": {
    "id": "Microsoft.Azure.Functions.ExtensionBundle",
    "version": "[4.*, 5.0.0)"
  }
}

Configure the connection in app settings. A connection string (stored as AzureSignalRConnectionString) or an identity-based connection is supported:

az functionapp config appsettings set \
  --name $APP_NAME \
  --resource-group $RG \
  --settings "AzureSignalRConnectionString__serviceUri=https://$SIGNALR_NAME.service.signalr.net"

The SignalR Service instance must be in Serverless mode. When using an identity-based connection, grant the function app's managed identity the SignalR Service Owner role on the resource.

The negotiate Endpoint¶

Before a client connects, it calls a negotiate endpoint to obtain the service URL and a short-lived access token. The SignalRConnectionInfo input binding produces this payload. Do not cache or share the token between clients.

const { app, input } = require("@azure/functions");

const inputSignalR = input.generic({
  type: "signalRConnectionInfo",
  name: "connectionInfo",
  hubName: "serverless",
  connectionStringSetting: "AzureSignalRConnectionString",
});

app.post("negotiate", {
  authLevel: "function",
  route: "negotiate",
  extraInputs: [inputSignalR],
  handler: (request, context) => {
    return { body: JSON.stringify(context.extraInputs.get(inputSignalR)) };
  },
});

Output Binding: Broadcast a Message¶

The SignalR output binding sends a message to all connected clients. The message object specifies a target (the client-side handler name) and arguments.

const { app, output } = require("@azure/functions");

const signalR = output.generic({
  type: "signalR",
  name: "signalRMessages",
  hubName: "serverless",
  connectionStringSetting: "AzureSignalRConnectionString",
});

app.http("broadcast", {
  methods: ["POST"],
  authLevel: "function",
  extraOutputs: [signalR],
  handler: async (request, context) => {
    const message = await request.text();

    context.extraOutputs.set(signalR, {
      target: "newMessage",
      arguments: [message],
    });

    return { status: 202 };
  },
});

Sending to a Specific User or Group¶

Add userId or groupName to the message object to target a subset of clients instead of broadcasting:

context.extraOutputs.set(signalR, {
  userId: "user1",
  target: "newMessage",
  arguments: [message],
});

See Also¶

• HTTP Authentication
• Managed Identity

Sources¶

• Azure Functions SignalR Service bindings (Microsoft Learn)
• SignalR Service input binding (Microsoft Learn)
• SignalR Service output binding (Microsoft Learn)