Azure Function not binding to appsettings when deployed

Question

I have an Azure Function app written in C# with Visual Studio using version 3.0.9 of Functions SDK. In the same directory as the csproj file and the host.json, I have an appsettings.json file with the following content:

{
    "test-queue": "test,
    "myOptions": {
      "batchSize": 5000
    }
}

The function works fine when I run it locally but for some reason it doesn't seem to bind to the appsettings file when it is deployed to Azure. I use the following startup class:

public class Startup : FunctionsStartup
{
    public override void ConfigureAppConfiguration(IFunctionsConfigurationBuilder builder)
    {
        builder.ConfigurationBuilder
            .SetBasePath(Environment.CurrentDirectory)
            .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
            .AddEnvironmentVariables();

        var builtConfig = builder.ConfigurationBuilder.Build();
        var keyVaultName = builtConfig["AzureKeyVaultName"];

        if (!string.IsNullOrEmpty(keyVaultName))
        {
            var azureServiceTokenProvider = new AzureServiceTokenProvider();
            var keyVaultClient = new KeyVaultClient(new KeyVaultClient.AuthenticationCallback(azureServiceTokenProvider.KeyVaultTokenCallback));

            builder.ConfigurationBuilder.AddAzureKeyVault($"https://{keyVaultName}.vault.azure.net/");
        }

        builder.ConfigurationBuilder
                .AddJsonFile("local.settings.json", true)
                .AddEnvironmentVariables()
                .Build();
    }

    public override void Configure(IFunctionsHostBuilder builder)
    {
        FunctionsHostBuilderContext context = builder.GetContext();
       
        builder.Services.AddOptions<MyOptions>()
            .Configure<IConfiguration>((settings, configuration) =>
            {
                configuration.GetSection("myOptions").Bind(settings);
            });
    }   
}

I have a function class like this:

public class MyFunction
{
    private readonly MyOptions options;

    public MyFunction(IOptions<MyOptions> options)
    {
        this.options = options.Value;
    }

    [FunctionName("Test")]
    public async Task Run(
        [QueueTrigger("%test-queue%")] MyParameters parameters,
        ILogger log)
    {
        log.LogInformation($"Batch size: {options.BatchSize}");
    }
}

The trouble is, the function doesn't seem to be using the appsettings file. I get an InvalidOperationException on startup saying '%test-queue%' does not resolve to a value." I can get rid of the queue binding and hard code the queue name. That makes the funtion run Okay but then the log file says the batch size is 0 instead of 5000.

Again, it works when running locally but not when it is deployed. The optional flag is false when registering the appsettings file in the startup so it must be getting found.

Connell.O'Donnell Connell.O'Donnell · Accepted Answer · 2020-10-06T15:31:35

I've got a partial solution by replacing

builder.ConfigurationBuilder
        .SetBasePath(Environment.CurrentDirectory)
        .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
        .AddEnvironmentVariables();

with

FunctionsHostBuilderContext context = builder.GetContext();

        builder.ConfigurationBuilder
            .AddJsonFile(Path.Combine(context.ApplicationRootPath, "appsettings.json"), optional: false, reloadOnChange: false)
            .AddEnvironmentVariables();

It is still making me hard code the queue names but batchSize variable is getting set at least.

Azure Function not binding to appsettings when deployed

1 Answers