Azure Function - CosmosDbTrigger - Bind variables from Keyvault and App configuration instead of appsettings

Question

I'm using .NET 6 and Azure functions v4. I would like to use Keyvault and App configuration (for non secure configuration) for bind variables in CosmosDbTrigger but have been unsuccessful.

For example:

        [Function("Function1")]
        public async Task Run([CosmosDBTrigger(
            databaseName: "%COSMOS_RAW_DATABASE%",
            containerName: "%COSMOS_RAW_CONTAINER_NAME%",
            Connection = "CONNECTION-COSMOS",
            LeaseContainerName = "leases",
            CreateLeaseContainerIfNotExists = true)] IReadOnlyList<object> input)
        {

databaseName, containerName, and Connection all should be driven from configuration. Ideally, databaseName and containerName will come from App Configuration and CONNECTION-COSMOS will come from Keyvault.

This function definition works if I have everything in local.settings.json (run locally) and in app settings of the function resource when deployed. However, I want to avoid storing in the settings in the resources appsettings.

When I try to set up Keyvault and App configuration as configuration providers, it works just fine but the functions seem to launch before I get in to Program.cs / Main so the configuration is not available and I get messages like this (below).

Does anyone have any guidance on how to set this up using configuration from Keyvault and App Configuration?

NOTE: I'm observing the same behavior both locally and deployed

Azure Functions Core Tools
Core Tools Version: 4.0.3971 Commit hash: d0775d487c93ebd49e9c1166d5c3c01f3c76eaaf (64-bit)
Function Runtime Version: 4.0.1.16815

[2021-11-11T00:37:51.846Z] Microsoft.Azure.WebJobs.Host: Error indexing method 'Functions.Function1'. Microsoft.Azure.WebJobs.Host: '%COSMOS_RAW_DATABASE%' does not resolve to a value.
[2021-11-11T00:37:51.862Z] Error indexing method 'Functions.Function1'
[2021-11-11T00:37:51.865Z] Microsoft.Azure.WebJobs.Host: Error indexing method 'Functions.Function1'. Microsoft.Azure.WebJobs.Host: '%COSMOS_RAW_DATABASE%' does not resolve to a value.
[2021-11-11T00:37:51.866Z] Function 'Functions.Function1' failed indexing and will be disabled.

Answer 1

@Mecomber, Michael This can be achieved by customizing configuration sources but this affects scaling in the consumption and premium tiers. The other option is to use KeyVault References instead.

Answer 2

For Azure Functions Isolated Model (Out-of-process), you can just whatever ASP.NET Core does.

Install Microsoft.Extensions.Configuration.AzureAppConfiguration NuGet package

using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Hosting;

namespace FunctionApp1;

public class Program
{
    public static void Main()
    {
        var host = new HostBuilder()
            .ConfigureFunctionsWorkerDefaults()
            .ConfigureAppConfiguration(config =>
            {
                IConfigurationRoot settings = config.Build();
                var connection = settings.GetConnectionString("ConnectionString");
                config.AddAzureAppConfiguration(connection);
            })
            .Build();

        host.Run();
    }
}