Logging to elmah.io from Isolated Azure Functions

Logging to elmah.io from Isolated Azure Functions

Logging errors from Isolated Azure Functions requires only a few lines of code. We've created clients specifically for Isolated Azure Functions. If your are looking for logging from Azure Functions (in process) check out Logging to elmah.io from Azure Functions.

Install the Elmah.Io.Functions.Isolated package in your project to get started:

Install-Package Elmah.Io.Functions.Isolated

dotnet add package Elmah.Io.Functions.Isolated

<PackageReference Include="Elmah.Io.Functions.Isolated" Version="5.*" />

paket add Elmah.Io.Functions.Isolated

Next, call the AddElmahIo method inside ConfigureFunctionsWorkerDefaults:

.ConfigureFunctionsWorkerDefaults((context, app) =>
{
    app.AddElmahIo(options =>
    {
        options.ApiKey = "API_KEY";
        options.LogId = new Guid("LOG_ID");
    });
})

Also, include a using of the Elmah.Io.Functions.Isolated namespace. elmah.io now automatically identifies any uncaught exceptions and logs them to the specified log. Check out the samples for more ways to configure elmah.io.

Application name

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

app.AddElmahIo(options =>
{
    // ...
    options.Application = "MyFunction";
});

Message hooks

Elmah.Io.Functions.Isolated 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 action:

app.AddElmahIo(options =>
{
    // ...
    options.OnMessage = msg =>
    {
        msg.Version = "1.0.0";
    };
});

The example above includes a version number on all errors.

Include source code

You can use the OnMessage action to include source code to log messages. This will require a stack trace in the Detail property with filenames and line numbers in it.

There are multiple ways of including source code to log messages. In short, you will need to install the Elmah.Io.Client.Extensions.SourceCode NuGet package and call the WithSourceCodeFromPdb method in the OnMessage action:

app.AddElmahIo(options =>
{
    // ...
    options.OnMessage = msg =>
    {
        msg.WithSourceCodeFromPdb();
    };
});

Check out How to include source code in log messages for additional requirements to make source code show up on elmah.io.

Handle errors

To handle any errors happening while processing a log message, you can use the OnError action:

app.AddElmahIo(options =>
{
    // ...
    options.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 action:

app.AddElmahIo(options =>
{
    // ...
    options.OnFilter = msg =>
    {
        return msg.Method == "GET";
    };
});

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

Logging through ILogger

Isolated Azure Functions can log through Microsoft.Extensions.Logging (MEL) too. 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

dotnet add package Elmah.Io.Extensions.Logging

<PackageReference Include="Elmah.Io.Extensions.Logging" Version="5.*" />

paket add Elmah.Io.Extensions.Logging

Then extend your Program.cs file like this:

var host = new HostBuilder()
    // ...
    .ConfigureLogging(logging =>
    {
        logging.AddElmahIo(options =>
        {
            options.ApiKey = "API_KEY";
            options.LogId = new Guid("LOG_ID");
        });
        logging.AddFilter<ElmahIoLoggerProvider>(null, LogLevel.Warning);
    })
    // ...
    .Build();

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. Jump to Log filtering to learn how to configure filters from config.

Either pass an ILogger to your function method:

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

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

public class MyFunction
{
    private readonly ILogger<MyFunction> logger;

    public Function1(ILoggerFactory loggerFactory)
    {
        this.logger = loggerFactory.CreateLogger<MyFunction>();
    }

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

Log filtering

The code above filters out all log messages with a severity lower than Warning. You can use all of the log filtering capabilities of Microsoft.Extensions.Logging to enable and disable various log levels from multiple categories. A common requirement is to only log Warning and more severe originating from the Azure Functions runtime, but log Information messages from your function code. This can be enabled through a custom category:

public class MyFunction
{
    public void Run([TimerTrigger("...")]TimerInfo myTimer, ILogger<MyFunction> logger)
    {
        logger.LogInformation("This is an information message");
    }
}

The MyFunction category will need configuration in either C# or in the host.json file:

{
  // ...
  "logging": {
    "logLevel": {
      "default": "Warning",
      "MyFunction": "Information"
    }
  }
}

Troubleshooting

Exceptions in Program.cs are not logged

Unfortunately, Azure Functions doesn't send exceptions happening in initialization code to the configured loggers. The only solution is to wrap your code in try/catch:

try
{
    var host = new HostBuilder()
        .ConfigureFunctionsWorkerDefaults((context, app) =>
        {
            app.AddElmahIo(options =>
            {
                options.ApiKey = "API_KEY";
                options.LogId = new Guid("LOG_ID");
            });
        })
        .Build();

    host.Run();
}
catch (Exception e)
{
    Console.Error.WriteLine(e);
    throw;
}

Next, go to the Log stream page on the Azure portal and inspect any errors logged.

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