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Logging to elmah.io from Azure Functions

Logging errors from Azure Functions, requires only a few lines of code. We've created a client specifically for Azure Functions.

Install the newest Elmah.Io.Functions prerelease package in your Azure Functions project:

Install-Package Elmah.Io.Functions -IncludePrerelease

The elmah.io integration for Azure Functions v2 uses function filters and dependency injection part of the Microsoft.Azure.Functions.Extensions package. To configure elmah.io, open the Startup.cs file or create a new one if not already there. In the Configure-method, add the elmah.io options and exception filter:

using Elmah.Io.Functions;
using Microsoft.Azure.Functions.Extensions.DependencyInjection;
using Microsoft.Azure.WebJobs.Host;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using System;

[assembly: FunctionsStartup(typeof(MyFunction.Startup))]

namespace MyFunction
{
    public class Startup : FunctionsStartup
    {
        public override void Configure(IFunctionsHostBuilder builder)
        {
            var config = new ConfigurationBuilder()
                .AddJsonFile("local.settings.json", optional: true, reloadOnChange: true)
                .AddEnvironmentVariables()
                .Build();

            builder.Services.Configure<ElmahIoFunctionOptions>(o =>
            {
                o.ApiKey = config["apiKey"];
                o.LogId = new Guid(config["logId"]);
            });

            builder.Services.AddSingleton<IFunctionFilter, ElmahIoExceptionFilter>();
        }
    }
}

Notice how API key and log ID are configured through the ElmahIoFunctionOptions object. In the last line of the Configure-method, the ElmahIoExceptionFilter-filter is configured. This filter will automatically catch any exception caused by your filter and log it to elmah.io.

In your settings, add the apiKeyand logId variables:

{
  ...
  "Values": {
    ...
    "apiKey": "API_KEY",
    "logId": "LOG_ID"
  }
}

Replace API_KEY with your API key (Where is my API key?) and LOG_ID (Where is my log ID?) with your log ID. When running on Azure or similar, you can overwrite apiKey and logId with application settings or environment variables as already thoroughly documented on Microsoft's documentation.

Application name

To set the application name on all errors, set the Application property during initialization:

builder.Services.Configure<ElmahIoFunctionOptions>(o =>
{
    o.ApiKey = config["apiKey"];
    o.LogId = new Guid(config["logId"]);
    o.Application = "MyFunction";
});

Message hooks

Elmah.Io.Functions provide message hooks similar to the integrations with ASP.NET and ASP.NET Core.

Decorating log messages

To include additional information on log messages, you can use the OnMessage event when initializing ElmahIoFunctionOptions:

builder.Services.Configure<ElmahIoFunctionOptions>(o =>
{
    o.ApiKey = config["apiKey"];
    o.LogId = new Guid(config["logId"]);
    o.OnMessage = msg =>
    {
        msg.Version = "1.0.0";
    };
});

The example above includes a version number on all errors.

Handle errors

To handle any errors happening while processing a log message, you can use the OnError event when initializing ElmahIoFunctionOptions:

builder.Services.Configure<ElmahIoFunctionOptions>(o =>
{
    o.ApiKey = config["apiKey"];
    o.LogId = new Guid(config["logId"]);
    o.OnError = (msg, ex) =>
    {
        logger.LogError(ex, ex.Message);
    };
});

The example above logs any errors during communication with elmah.io to a local log.

Error filtering

To ignore specific errors based on their content, you can use the OnFilter event when initializing ElmahIoFunctionOptions:

builder.Services.Configure<ElmahIoFunctionOptions>(o =>
{
    o.ApiKey = config["apiKey"];
    o.LogId = new Guid(config["logId"]);
    o.OnFilter = msg =>
    {
        return msg.Method == "GET";
    };
});

The example above ignores any errors generated during an HTTP GET request.

Logging through ILogger

Azure Functions can log through Microsoft.Extensions.Logging (MEL) too. By adding the filter, as shown above, all uncaught exceptions are automatically logged. But when configuring your Function app to log through MEL, custom messages can be logged through the ILogger interface. Furthermore, you will get detailed log messages from within the Function host. To set this up, install the Elmah.Io.Extensions.Logging NuGet package:

Install-Package Elmah.Io.Extensions.Logging -IncludePrerelease

Then extend your Startup.cs file like this:

builder.Services.AddLogging(logging =>
{
    logging.AddElmahIo(o =>
    {
        o.ApiKey = config["apiKey"];
        o.LogId = new Guid(config["logId"]);
    });
    logging.AddFilter<ElmahIoLoggerProvider>(null, LogLevel.Warning);
});

In the example, only warning messages and above are logged to elmah.io. You can remove the filter or set another log level if you want to log more.

Either pass an ILogger to your function method:

public class MyFunction
{
    public static void Run([TimerTrigger("...")]TimerInfo myTimer, ILogger log)
    {
        log.LogWarning("This is a warning");
    }
}

Or inject an ILoggerFactory and create a logger as part of the constructor:

public class MyFunction
{
    private readonly ILogger log;

    public Function1(ILoggerFactory loggerFactory)
    {
        this.log = loggerFactory.CreateLogger("MyFunction");
    }

    public void Run([TimerTrigger("...")]TimerInfo myTimer)
    {
        log.LogWarning("This is a warning");
    }
}

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