Tuesday, February 20, 2024

.NET 8.0 Isolated Azure Functions: Binding Expressions that uses Azure App Configuration

In this post let's see how we can use binding expressions in an .NET 8.0 Isolated Azure Function and how to consume the binding expression values from Azure App Configuration (AAC).

Binding expressions are basically something like this. Let's take a simple ServiceBus trigger function. 
public static void ServiceBusTrigger( [ServiceBusTrigger("%Messaging:Topic%", "%Messaging:Subscription%")] ServiceBusReceivedMessage serviceBusReceivedMessage)
    // TODO: Process the received message
Here the  %Messaging:Topic% and %Messaging:Subscription% are binding expressions and its value doesn't have to be a compile time constant.

In In-Process Azure functions, it's pretty straightforward, you can just add Azure App Configuration as another configuration provider in the Startup, and it will work.

But in Isolated functions at least as of today (20th February 2024), you can't do that (Support expression resolution from configuration sources registered by the worker #1253). While it's a bit disappointing (after having Isolated functions available for a couple of years), you can use the following workaround.

Let's say I have the following values in my Azure App Configuration.
Azure App Configuration
Azure App Configuration Values
I can use the following notation to access AAC values.
@Microsoft.AppConfiguration(Endpoint=https://aac-temp-001.azconfig.io; Key=<key>)
// if you want to choose a particular Label
@Microsoft.AppConfiguration(Endpoint=https://aac-temp-001.azconfig.io; Key=<key>; Label=<label>)
So I can update Function App settings in Azure as follows. Make sure the identity of the function app (system-assigned managed identity or user-assigned managed identity) can read the configuration from AAC.
Function App Configuration
More read:
   Use App Configuration references for App Service and Azure Functions (preview)

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