Logging to elmah.io from Serilog

Logging to elmah.io from Serilog

Serilog is a great addition to the flowering .NET logging community, described as “A no-nonsense logging library for the NoSQL era” on their project page. Serilog works just like other logging frameworks such as log4net and NLog, but offers a great fluent API and the concept of sinks (a bit like appenders in log4net). Sinks are superior to appenders, because they threat errors as objects rather than strings, a perfect fit for elmah.io which itself is built on NoSQL. Serilog already comes with native support for elmah.io, which makes it easy to integrate with any application using Serilog.

In this example we’ll use a ASP.NET MVC project as an example. Neither Serilog nor elmah.io are bound to log errors from web applications. Adding this type of logging to your windows and console applications is just as easy. Add the Serilog.Sinks.ElmahIo NuGet package to your project:

Install-Package Serilog.Sinks.ElmahIo

dotnet add package Serilog.Sinks.ElmahIo

<PackageReference Include="Serilog.Sinks.ElmahIo" Version="3.*" />

paket add Serilog.Sinks.ElmahIo

To configure Serilog, add the following code to the Application_Start method in global.asax.cs:

var log =
    new LoggerConfiguration()
        .WriteTo.ElmahIo(new ElmahIoSinkOptions("API_KEY", new Guid("LOG_ID")))
        .CreateLogger();
Log.Logger = log;

Replace API_KEY with your API key (Where is my API key?) and LOG_ID with the ID of the log you want messages sent to (Where is my log ID?).

First, we create a new LoggerConfiguration and tell it to write to elmah.io. The log object can be used to log errors and you should register this in your IoC container. In this case, we don’t use IoC, that is why the log object is set as the public static Logger property, which makes it accessible from everywhere.

To log log exceptions to elmah.io through Serilog, is the Log class provided by Serilog:

try {
    // Do some stuff which may cause an exception
}
catch (Exception e) {
    Log.Error(e, "The actual error message");
}

The Error method tells Serilog to log the error in the configured sinks, which in our case logs to elmah.io. Simple and beautiful.

Always call Log.CloseAndFlush(); before your program terminates.

Logging custom properties

Serilog support logging custom properties in three ways: As part of the log message, through enrichers and using LogContext. All three types of properties are implemented in the elmah.io sink as part of the Data dictionary to elmah.io.

The following example shows how to log all three types of properties:

var logger =
    new LoggerConfiguration()
        .Enrich.WithProperty("ApplicationIdentifier", "MyCoolApp")
        .Enrich.FromLogContext()
        .WriteTo.ElmahIo(new ElmahIoSinkOptions("API_KEY", new Guid("LOG_ID")))
        .CreateLogger();

using (LogContext.PushProperty("ThreadId", Thread.CurrentThread.ManagedThreadId))
{
    logger.Error("This is a message with {Type} properties", "custom");
}

Beneath the Data tab on the logged message details, the ApplicationIdentifier, ThreadId and Type properties can be found.

Serilog.Sinks.ElmahIo provides a range of reserved property names, that can be used to fill in data in the correct fields on the elmah.io UI. Let's say you want to fill the User field using structured logging only:

logger.Information("{Quote} from {User}", "Hasta la vista, baby", "Arnold Schwarzenegger");

This will fill in the value Arnold Schwarzenegger in the User field, as well as add two key/value pairs (Quote and User) to the Data tab on elmah.io. For a reference of all possible property names, check out the property names on CreateMessage.

Message hooks

Serilog.Sinks.ElmahIo provide message hooks similar to the integrations with ASP.NET and ASP.NET Core.

Message hooks require Serilog.Sinks.ElmahIo version 3.3.0 or newer.

Decorating log messages

To include additional information on log messages, you can use the OnMessage event when initializing the elmah.io target:

Log.Logger =
    new LoggerConfiguration()
        .WriteTo.ElmahIo(new ElmahIoSinkOptions("API_KEY", new Guid("LOG_ID"))
        {
            OnMessage = msg =>
            {
                msg.Version = "1.0.0";
            }
        })
        .CreateLogger();

The example above includes a version number on all errors. Since the elmah.io sink also picks up encrichers specified with Serilog, this example could be implemented by enriching all log messages with a field named version.

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:

Log.Logger =
    new LoggerConfiguration()
        .WriteTo.ElmahIo(new ElmahIoSinkOptions("API_KEY", new Guid("LOG_ID"))
        {
            OnMessage = msg =>
            {
                msg.WithSourceCodeFromPdb();
            }
        })
        .CreateLogger();

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

Including source code on log messages is currently available in the Elmah.Io.Client v4 prerelease only.

Handle errors

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

Log.Logger =
    new LoggerConfiguration()
        .WriteTo.ElmahIo(new ElmahIoSinkOptions("API_KEY", new Guid("LOG_ID"))
        {
            OnError = (msg, ex) =>
            {
                Console.Error.WriteLine(ex.Message);
            }
        })
        .CreateLogger();

The example implements a callback if logging to elmah.io fails. How you choose to implement this is entirely up to your application and tech stack.

Error filtering

To ignore specific messages based on their content, you can use the OnFilter event when initializing the elmah.io sink:

Log.Logger =
    new LoggerConfiguration()
        .WriteTo.ElmahIo(new ElmahIoSinkOptions("API_KEY", new Guid("LOG_ID"))
        {
            OnFilter = msg =>
            {
                return msg.Title.Contains("trace");
            }
        })
        .CreateLogger();

The example above ignores any log message with the word trace in the title.

ASP.NET Core

Serilog provides a package for ASP.NET Core, that routes log messages from inside core through Serilog. We recommend to use this package together with the elmah.io sink, in order to capture warnings and errors happening inside ASP.NET Core.

To use this, install the following packages:

Install-Package Serilog.AspNetCore
Install-Package Serilog.Sinks.ElmahIo

dotnet add package Serilog.AspNetCore
dotnet add package Serilog.Sinks.ElmahIo

<PackageReference Include="Serilog.AspNetCore" Version="3.*" />
<PackageReference Include="Serilog.Sinks.ElmahIo" Version="3.*" />

paket add Serilog.AspNetCore
paket add Serilog.Sinks.ElmahIo

Configure Serilog as usual:

public static int Main(string[] args)
{
    Log.Logger = new LoggerConfiguration()
        .WriteTo.ElmahIo(new ElmahIoSinkOptions("API_KEY", new Guid("LOG_ID"))
        {
            MinimumLogEventLevel = Events.LogEventLevel.Warning
        })
        .CreateLogger();

    try
    {
        CreateWebHostBuilder(args).Build().Run();
        return 0;
    }
    catch (Exception ex)
    {
        Log.Fatal(ex, "Host terminated unexpectedly");
        return 1;
    }
    finally
    {
        Log.CloseAndFlush();
    }
}

Finally, call the UseSerilog-method in BuildWebHost:

public static IWebHost BuildWebHost(string[] args) =>
    WebHost
        .CreateDefaultBuilder(args)
        .UseStartup<Startup>()
        .UseSerilog();

Now, all warnings, errors and fatals happening inside ASP.NET Core are logged to elmah.io.

A common request is to include all of the HTTP contextual information you usually get logged when using a package like Elmah.Io.AspNetCore. We have developed a specialized NuGet package to include cookies, server variables, etc. when logging through Serilog from ASP.NET Core. To set it up, install the Elmah.Io.AspNetCore.Serilog NuGet package:

Install-Package Elmah.Io.AspNetCore.Serilog

dotnet add package Elmah.Io.AspNetCore.Serilog

<PackageReference Include="Elmah.Io.AspNetCore.Serilog" Version="3.*" />

paket add Elmah.Io.AspNetCore.Serilog

Then, call the UseElmahIoSerilog method in the Configure method in the Startup.cs file:

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
{
    // ... Exception handling middleware
    app.UseElmahIoSerilog();
    // ... UseMvc etc.
}

The middleware uses Serilog's LogContext feature to enrich each log message with additional properties. To turn on the log context, extend your Serilog config:

Log.Logger = new LoggerConfiguration()
    .WriteTo.ElmahIo(/*...*/)
    .Enrich.FromLogContext() // <-- add this line
    .CreateLogger();

Config using appsettings.json

While Serilog provides a great fluent C# API, some prefer to configure Serilog using an appsettings.json file. To configure the elmah.io sink this way, you will need to install the Serilog.Settings.Configuration NuGet package. Then configure elmah.io in your appsettings.json file:

{
    // ...
    "Serilog":{
        "Using":[
            "Serilog.Sinks.ElmahIo"
        ],
        "MinimumLevel": "Warning",
        "WriteTo":[
            {
                "Name": "ElmahIo",
                "Args":{
                    "apiKey": "API_KEY",
                    "logId": "LOG_ID"
                }
            }
        ]
    }
}

Make sure to specify the apiKey and logId arguments with the first character in lowercase.

Finally, tell Serilog to read the configuration from the appsettings.json file:

var configuration = new ConfigurationBuilder()
    .AddJsonFile("appsettings.json")
    .Build();

var logger = new LoggerConfiguration()
    .ReadFrom.Configuration(configuration)
    .CreateLogger();

Extended exception details with Serilog.Exceptions

The more information you have on an error, the easier it is to find out what went wrong. Muhammad Rehan Saeed made a nice enrichment package for Serilog named Serilog.Exceptions. The package uses reflection on a logged exception to log additional information depending on the concrete exception type. You can install the package through NuGet:

Install-Package Serilog.Exceptions

dotnet add package Serilog.Exceptions

<PackageReference Include="Serilog.Exceptions" Version="5.*" />

paket add Serilog.Exceptions

And configure it in C# code:

var logger = new LoggerConfiguration()
    .Enrich.WithExceptionDetails()
    .WriteTo.ElmahIo(/*...*/)
    .CreateLogger();

The elmah.io sink will automatically pick up the additional information and show them in the extended message details overlay. To navigate to this view, click an error on the search view. Then click the button in the upper right corner to open extended message details. The information logged by Serilog.Exceptions are available beneath the Data tab.

Remove sensitive data

Structured logging with Serilog is a great way to store a lot of contextual information about a log message. In some cases, it may result in sensitive data being stored in your log, though. We recommend you to remove any sensitive data from your log messages before storing them on elmah.io and anywhere else. To implement this, you can use the OnMessage event as already shown previously in the document:

OnMessage = msg =>
{
    foreach (var d in msg.Data)
    {
        if (d.Key.Equals("Password"))
        {
            d.Value = "****";
        }
    }
}

An alternative to replacing sensitive values manually is to use a custom destructuring package for Serilog. The following example shows how to achieve this using the Destructurama.Attributed package:

Install-Package Destructurama.Attributed

dotnet add package Destructurama.Attributed

<PackageReference Include="Destructurama.Attributed" Version="2.*" />

paket add Destructurama.Attributed

Set up destructuring from attributes:

Log.Logger = new LoggerConfiguration()
    .Destructure.UsingAttributes()
    .WriteTo.ElmahIo(/*...*/)
    .CreateLogger();

Make sure to decorate any properties including sensitive data with the NotLogged attribute:

public class LoginModel
{
    public string Username { get; set; }

    [NotLogged]
    public string Password { get; set; }
}

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