Logging to elmah.io from Microsoft.Extensions.Logging

Microsoft.Extensions.Logging is both a logging framework itself and a logging abstraction on top of other logging frameworks like log4net and Serilog.

Start by installing the Elmah.Io.Extensions.Logging 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

Locate your API key (Where is my API key?) and log ID. The two values will be referenced as API_KEY and LOG_ID (Where is my log ID?) in the following.

Logging from ASP.NET Core

In the Program.cs file, add a new using statement:

using Elmah.Io.Extensions.Logging;

Then call the AddElmahIo-method as shown here:

builder.Logging.AddElmahIo(options =>
{
    options.ApiKey = "API_KEY";
    options.LogId = new Guid("LOG_ID");
});
builder.Logging.AddFilter<ElmahIoLoggerProvider>(null, LogLevel.Warning);

By calling, the AddFilter-method, you ensure that only warnings and up are logged to elmah.io.

The API key and log ID can also be configured in appsettings.json:

{
  // ...
  "ElmahIo": {
    "ApiKey": "API_KEY",
    "LogId": "LOG_ID"
  }
}

To tell Microsoft.Extensions.Logging to use configuration from the appsettings.json file, include the following code in Program.cs:

builder.Services.Configure<ElmahIoProviderOptions>(builder.Configuration.GetSection("ElmahIo"));
builder.Logging.AddConfiguration(builder.Configuration.GetSection("Logging"));
builder.Logging.AddElmahIo();

The first line fetches elmah.io configuration from the ElmahIo object in the appsettings.json file. The second line configures log levels in Microsoft.Extensions.Logging from the Logging object in appsettings.json. The third line adds the elmah.io logger to Microsoft.Extensions.Logging. Notice how the overload without any options object is called since options are already loaded from appsettings.json.

Start logging messages by injecting an ILogger in your controllers:

public class HomeController : Controller
{
    private readonly ILogger<HomeController> logger;

    public HomeController(ILogger<HomeController> logger)
    {
        this.logger = logger;
    }

    public IActionResult Index()
    {
        logger.LogWarning("Request to index");
        return View();
    }
}

Include HTTP context

A common use case for using Microsoft.Extensions.Logging is part of an ASP.NET Core project. When combining the two, you would expect the log messages to contain relevant information from the HTTP context (like URL, status code, cookies, etc.). This is not the case out of the box, since Microsoft.Extensions.Logging doesn't know which project type includes it.

To add HTTP context properties to log messages when logging from ASP.NET Core, install the Elmah.Io.AspNetCore.ExtensionsLogging NuGet package:

Install-Package Elmah.Io.AspNetCore.ExtensionsLogging

dotnet add package Elmah.Io.AspNetCore.ExtensionsLogging

<PackageReference Include="Elmah.Io.AspNetCore.ExtensionsLogging" Version="5.*" />

paket add Elmah.Io.AspNetCore.ExtensionsLogging

Then call the UseElmahIoExtensionsLogging method in the Program.cs file:

// ... Exception handling middleware
app.UseElmahIoExtensionsLogging();
// ... UseMvc etc.

It's important to call the UseElmahIoExtensionsLogging method after any calls to UseElmahIo, UseAuthentication, and other exception handling middleware but before UseMvc and UseEndpoints. If you experience logged errors without the HTTP context, try moving the UseElmahIoExtensionsLogging method as the first call in the Configure method.

Logging from a console application

Choose the right framework version:

var services = new ServiceCollection();
services.AddLogging(logging => logging.AddElmahIo(options =>
{
    options.ApiKey = "API_KEY";
    options.LogId = new Guid("LOG_ID");
}));

using var serviceProvider = services.BuildServiceProvider();
var loggerFactory = serviceProvider.GetService<ILoggerFactory>();

using var loggerFactory = LoggerFactory.Create(builder => builder
    .AddElmahIo(options =>
    {
        options.ApiKey = "API_KEY";
        options.LogId = new Guid("LOG_ID");
    }));

Adding the using keyword is important to let elmah.io store messages before exiting the application.

Finally, create a new logger and start logging exceptions:

var logger = factory.CreateLogger("MyLog");
logger.LogError(ex, "Unexpected error");

Logging custom properties

Elmah.Io.Extensions.Logging support Microsoft.Extensions.Logging scopes from version 3.6.x. In short, scopes are a way to decorate your log messages like enrichers in Serilog and context in NLog and log4net. By including properties in a scope, these properties automatically go into the Data tab on elmah.io.

To define a new scope, wrap your logging code in a using:

using (logger.BeginScope(new Dictionary<string, object> { { "UserId", 42 } }))
{
    logger.LogInformation("Someone says hello");
}

In the example above, the UserId key will be added on the Data tab with the value of 42.

Like the other logging framework integrations, Elmah.Io.Extensions.Logging supports a range of known keys that can be used to insert value in the correct fields on the elmah.io UI.

using (logger.BeginScope(new Dictionary<string, object>
    { { "statuscode", 500 }, { "method", "GET" } }))
{
    logger.LogError("Request to {url} caused an error", "/profile");
}

In this example, a log message with the template Request to {url} caused an error to be logged. The use of the variable names statuscode, method, and url will fill in those values in the correct fields on elmah.io. For a reference of all possible property names, check out the property names on CreateMessage.

An alternative is to use the OnMessage action. As an example, we'll add a version number to all messages:

logging
    .AddElmahIo(options =>
    {
        // ...
        options.OnMessage = msg =>
        {
            msg.Version = "2.0.0";
        };
    });

You can even access the current HTTP context in the OnMessage action. To do so, start by creating a new class named DecorateElmahIoMessages:

public class DecorateElmahIoMessages : IConfigureOptions<ElmahIoProviderOptions>
{
    private readonly IHttpContextAccessor httpContextAccessor;

    public DecorateElmahIoMessages(IHttpContextAccessor httpContextAccessor)
    {
        this.httpContextAccessor = httpContextAccessor;
    }

    public void Configure(ElmahIoProviderOptions options)
    {
        options.OnMessage = msg =>
        {
            var context = httpContextAccessor.HttpContext;
            if (context == null) return;
            msg.User = context.User?.Identity?.Name;
        };
    }
}

Then register IHttpContextAccessor and the new class in the Program.cs file:

builder.Services.AddHttpContextAccessor();
builder.Services.AddSingleton<IConfigureOptions<ElmahIoProviderOptions>, DecorateElmahIoMessages>();

Setting category

elmah.io provide a field named Category to better group log messages by class name, namespace, or similar. Category maps to Microsoft.Extensions.Logging field of the same name. The category field is automatically set when using a typed logger:

ILogger<MyType> logger = ...;
logger.LogInformation("This is an information message with category");

The category can be overwritten using a property named category on either the log message or a new scope:

using (logger.BeginScope(new Dictionary<string, object> { { "category", "The category" } }))
{
    logger.LogInformation("This is an information message with category");
}

Logging with LoggerMessage

.NET 6 introduced the LoggerMessage attribute that uses source generators for highly usable and performant log statements. Elmah.Io.Extensions.Logging fully supports log messages sent through logger messages.

[LoggerMessage(Level = LogLevel.Information, Message = "Created {UserId}")]
private static partial void LogUserCreated(ILogger logger, int userId);

// ...

LogUserCreated(logger, 42);

This will log a message saying Created 42 to elmah.io. Remember that the class including the LogUserCreated method needs to be declared as partial as well.

.NET 8 extends this even further by offering a new LogProperties attribute:

[LoggerMessage(Level = LogLevel.Information, Message = "Created user")]
private static partial void LogUserCreated(ILogger logger, [LogProperties]User user);

// ...

LogUserCreated(logger, new User
{
    Firstname = "Tyrion",
    Lastname = "Lannister"
});

By adding the LogProperties attribute to the User parameter, a log message saying Created user will be sent to elmah.io. In addition, the Data tab on the extended log message details will show the keys user.Firstname and user.Lastname with the values from the User object provided for the LogUserCreated method.

Include source code

You can use the OnMessage action already described 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:

logging
    .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.

Options

Setting application name

If logging to the same log from multiple applications it is a good idea to set unique application names from each app. This will let you search and filter errors on the elmah.io UI. To set an application name, add the following code to the options:

logging.AddElmahIo(options =>
{
    // ...
    options.Application = "MyApp";
});

The application name can also be configured through appsettings.json:

{
  // ...
  "ElmahIo": {
    // ...
    "Application": "MyApp"
  }
}

appsettings.json configuration

Some of the configuration for Elmah.Io.Extensions.Logging can be done through the appsettings.json file when using ASP.NET Core 2.x or above. To configure the minimum log level, add a new logger named ElmahIo to the settings file:

{
  "Logging": {
    // ...
    "ElmahIo": {
      "LogLevel": {
        "Default": "Warning"
      }
    }
  }
}

Finally, tell the logger to look for this information, by adding a bit of code to Program.cs:

builder.Logging.AddConfiguration(builder.Configuration.GetSection("Logging"));

Filtering log messages

As default, the elmah.io logger for Microsoft.Extensions.Logging only logs warnings, errors, and fatals. The rationale behind this is that we build an error management system and doesn't do much to support millions of debug messages from your code. Sometimes you may want to log non-exception messages, though. To do so, use filters in Microsoft.Extensions.Logging.

To log everything from log level Information and up, do the following:

Inside Program.cs change the minimum level:

builder.Logging.AddFilter<ElmahIoLoggerProvider>(null, LogLevel.Information);

In the code sample, every log message with a log level of Information and up will be logged to elmah.io.

Logging through a proxy

You can log through a proxy using options:

logging.AddElmahIo(options =>
{
    // ...
    options.WebProxy = new WebProxy("localhost", 8000);
});

In this example, the elmah.io client routes all traffic through http://localhost:8000.

Microsoft.Extensions.Logging Troubleshooting

Here are some things to try out if logging from Microsoft.Extensions.Logging to elmah.io doesn't work:

• Run the diagnose command with the elmah.io CLI as shown here: Diagnose potential problems with an elmah.io installation.

x message(s) dropped because of queue size limit

If you see this message in your log, it means that you are logging a large number of messages to elmah.io through Microsoft.Extensions.Logging within a short period of time. Either turn down the volume using filters:

logging.AddElmahIo(options => { /*...*/ });
logging.AddFilter<ElmahIoLoggerProvider>(null, LogLevel.Warning);

or increase the queue size of Elmah.Io.Extensions.Logging:

logging.AddElmahIo(options =>
{
    // ...
    options.BackgroundQueueSize = 5000;
});

Uncaught errors are logged twice

If you have both Elmah.Io.Extensions.Logging and Elmah.Io.AspNetCore installed, you may see a pattern of uncaught errors being logged twice. This is because a range of middleware from Microsoft (and others) log uncaught exceptions through ILogger. When you have Elmah.Io.AspNetCore installed you typically don't want other pieces of middleware to log the same error but with fewer details.

To ignore duplicate errors you need to figure out which middleware class that trigger the logging and in which namespace it is located. One or more of the following ignore filters can be added to your Program.cs file:

logging.AddFilter<ElmahIoLoggerProvider>(
    "Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware", LogLevel.None);
logging.AddFilter<ElmahIoLoggerProvider>(
    "Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware", LogLevel.None);
logging.AddFilter<ElmahIoLoggerProvider>(
    "Microsoft.AspNetCore.Server.IIS.Core", LogLevel.None);

Be aware that these lines will ignore all messages from the specified class or namespace. To ignore specific errors you can implement the OnFilter action as shown previously in this document. Ignoring uncaught errors from IIS would look like this:

options.OnFilter = msg =>
{
    return msg.TitleTemplate == "Connection ID \"{ConnectionId}\", Request ID \"{TraceIdentifier}\": An unhandled exception was thrown by the application.";
};

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