Use Azure SignalR Local Emulator for serverless development

2024-12-11

When developing serverless applications, we provide an Azure SignalR Local Emulator to make the local development and integration easier. The emulator works only for serverless scenarios, for Default mode that the Azure SignalR Service acts as a proxy, you can directly use self-host SignalR to do local development. Also note that emulator only works for Transient transport type (the default one) and doesn't support Persistent transport type.

Features available

Auth
Latest Rest API support
Upstream

Important

Raw connection strings appear in this article for demonstration purposes only.

A connection string includes the authorization information required for your application to access Azure SignalR Service. The access key inside the connection string is similar to a root password for your service. In production environments, always protect your access keys. Use Azure Key Vault to manage and rotate your keys securely and secure your connection string using Microsoft Entra ID and authorize access with Microsoft Entra ID.

Avoid distributing access keys to other users, hard-coding them, or saving them anywhere in plain text that is accessible to others. Rotate your keys if you believe they may have been compromised.

Walkthrough

We use this serverless sample to show how to use the emulator.

Raw connection strings appear in this article for demonstration purposes only. In production environments, always protect your access keys. Use Azure Key Vault to manage and rotate your keys securely and secure your connection string using Microsoft Entra ID and authorize access with Microsoft Entra ID.

Clone the sample repo to local

git clone https://github.com/Azure/azure-functions-signalrservice-extension.git
cd azure-functions-signalrservice-extension/samples/bidirectional-chat

Install the emulator

dotnet tool install  -g Microsoft.Azure.SignalR.Emulator

Or update the emulator to the latest preview version if it's already installed:

dotnet tool update -g Microsoft.Azure.SignalR.Emulator

Run the emulator asrs-emulator to list all the available commands
Init the default upstream settings using:
```
asrs-emulator upstream init
```
It creates a default settings.json into the current folder, with a default upstream UrlTemplate as http://localhost:7071/runtime/webhooks/signalr, which is the URL for SignalR's local function trigger:
```
{
"UpstreamSettings": {
    "Templates": [
    {
        "UrlTemplate": "http://localhost:7071/runtime/webhooks/signalr",
        "EventPattern": "*",
        "HubPattern": "*",
        "CategoryPattern": "*"
    }
    ]
}
}
```
You could edit the file to make the pattern more restricted, for example, change HubPattern from * to chat. When the file is modified, its change is hot-loaded into the emulator.
Start the emulator
```
asrs-emulator start
```
After the emulator is successfully started, it generates the ConnectionString to be used later.

The emulator also provides advanced options when start, for example, you can use asrs-emulator start -p 8999 to customize the port the emulator used. Type asrs-emulator start --help to check the options available.
Go into subfolder csharp and rename local.settings.sample.json to local.settings.json, use the ConnectionString generated by the emulator to fill into the value of the AzureSignalRConnectionString in your local.settings.json. Fill into AzureWebJobsStorage your storage connection string, for example, UseDevelopmentStorage=true when using storage emulator. Save the file and run the function in the csharp subfolder with func start.
In the browser, navigate to http://localhost:7071/api/index to play with the demo.

Next steps

In this article, you learn how to use SignalR Service in your applications. Check the following articles to learn more about SignalR Service.

Azure SignalR Service internals

Quickstart: Create a chat room by using SignalR Service

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