AspNetCore Kestrel: change your application port using a configuration file

Modern AspNetCore applications use the built-in web server kestrel,this server is usually bound to the localhost address using the ports 5000 and 5001 for http and https.

But what if you want to run 2 applications in the same server? then you have a problem because if you use the default ports one of the applications will not start correctly.

This can easily be solved by changing the default ports in your WebHostBuilder as shown below

public static IHostBuilder CreateHostBuilder(string[] args) =>
    Host.CreateDefaultBuilder(args)
   .ConfigureWebHostDefaults(webBuilder => {
       webBuilder.UseUrls("http://0.0.0.0:8016");
       webBuilder.UseStartup<Startup>();
   });

The problem with the example above is that the URLs are hardcoded, so here is a better solution

public static IHostBuilder CreateHostBuilder(string[] args) =>
  Host.CreateDefaultBuilder(args)
  .ConfigureWebHostDefaults(webBuilder => {
      var config = new ConfigurationBuilder()
      .SetBasePath(Directory.GetCurrentDirectory())
      .AddJsonFile("hosting.json", optional: true)
      .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
      .AddCommandLine(args)
      .AddEnvironmentVariables()
      .Build();

      webBuilder.UseUrls(config["server.urls"]);
      webBuilder.UseStartup<Startup>();
  });

the example above uses a configuration builder to merge the appsettings.json and the hosting.json in a single configuration object, then with use the value of the property “server.urls” as base URL/port for our application

Here is the content of the hosting.json file

{
    "server.urls": "http://0.0.0.0:8016" 
}