Scaling Web Push Notifications with Azure Functions

One of my talks is talk about native real-time technologies like WebSockets, Server-Sent Events, and Web Push in ASP.NET Core. In that talk, I briefly go through the subject of scaling applications based on those technologies. For Web Push, I mention that it can be scaled with help of microservices or functions, because it doesn't require an active HTTP request/response. After the talk, I'm frequently asked for some samples of how to do that. This post is me finally putting one together.

Sending Web Push Notifications from Azure Functions

I've written a series of posts about Web Push Notifications. In general, it's good to understand one level deeper than what you're working at (so I encourage you to go through that series), but for this post, it's enough to know that you can grab a client from NuGet. This client is all that is needed to send a notification from Azure Function, so let's quickly create one.

The function will use Azure Cosmos DB as a data source. Whenever an insert or update happens in NotificationsCollection, the function will be triggered.

public static class SendNotificationFunction
{
    [FunctionName("SendNotification")]
    public static void Run(
        [CosmosDBTrigger("PushNotifications", "NotificationsCollection",
        LeaseCollectionName = "NotificationsLeaseCollection", CreateLeaseCollectionIfNotExists = true,
        ConnectionStringSetting = "CosmosDBConnection")]
        IReadOnlyList<PushMessage> notifications)
    {

    }
}

You may notice that it's using an extension for Azure Cosmos DB Trigger described in my previous post, which allows for taking a collection of POCOs