LoggingandDiagnostics.md

Module 6: Logging and Diagnostics

Module goals: How to add logging to your application

• Setup your app for logging
• How to filter logs
• Add 3rd party logging provideres
• Web logging

Watch: Getting Started with Logging and Diagnostics here

Setup for logging

• Use application from introduction into ASP.NET Core 1.0
• Add or verify the Microsoft.Extensions.Logging.Console package to the project.json

      "dependencies": {
        "Microsoft.Extensions.Logging.Console": "1.0.0"
      },

• Open Startup.cs and update the configure method

        public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
        {
            loggerFactory.AddConsole();

            var startupLogger = loggerFactory.CreateLogger<Startup>();
            ...
        }

• Include a log statement to the Configure method

        public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
        {
            loggerFactory.AddConsole();

            var startupLogger = loggerFactory.CreateLogger<Startup>();

            startupLogger.LogInformation("Startup is complete!");
        }

• Change the Debug drop down in the toolbar to the application name and run the the application

Filtering Logs

• Ad a couple more logging statements

 startupLogger.LogCritical("This is a critical message");
    startupLogger.LogDebug("This is a debug message");
    startupLogger.LogTrace("This is a trace message");
    startupLogger.LogWarning("This is a warning message");
    startupLogger.LogError("This is an error message");

• Change the minimum log level for the console logger in Startup.cs:

    public void Configure(IApplicationBuilder app, ILoggerFactory loggerFactory)
    {
        loggerFactory.AddConsole(LogLevel.Trace);
        ...
    }

• Run the application

Adding other logging providers

• Add [serilog logger](Serilog logger) provider as dependency in project.json

    "dependencies": {
      ...
      "Serilog.Extensions.Logging":  "1.0.0",
      "Serilog.Sinks.File": "2.0.0"
    },

• Configure Serilog in Startup.cs to write to a file called logfile.txt in the project root (resolving usings for System.IO and Serilog):

   public Startup(IHostingEnvironment env)
   {
       Configuration = new ConfigurationBuilder()
                           .SetBasePath(env.ContentRootPath)
                           .AddJsonFile("appsettings.json")
                           .Build();

       var logFile = Path.Combine(env.ContentRootPath, "logfile.txt");

       Log.Logger = new LoggerConfiguration()
           .WriteTo.File(logFile)
           .CreateLogger();
   }
   ```
- Add the Serilog provider in `Configure`:

   ```C#
   public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
   {
       loggerFactory.AddConsole();
       loggerFactory.AddSerilog();
       ...
   }
   ```
- Run the application and open a browser window with `http://localhost:8081/` as the address. You should observe a file called `logfile.txt` appear in your application root. 
- Close the conosle window and open the file, the application logs should be in there.