Automatically set appsettings.json for dev and rel

Question

I've defined some values in my appsettings.json for things like database connection strings, webapi locations and the like which are different for development, staging and live environments.

Is there a way to have multiple appsettings.json files (like appsettings.live.json, etc, etc) and have the asp.net app just 'know' which one to use based on the build configuration it's running?

Answer 1

You can make use of environment variables and the ConfigurationBuilder class in your Startup constructor like this:

public Startup(IHostingEnvironment env)
{
    var builder = new ConfigurationBuilder()
    .SetBasePath(env.ContentRootPath)
    .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
    .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true)
    .AddEnvironmentVariables();
    this.configuration = builder.Build();
}

Then you create an appsettings.xxx.json file for every environment you need, with "xxx" being the environment name. Note that you can put all global configuration values in your "normal" appsettings.json file and only put the environment specific stuff into these new files.

Now you only need an environment variable called ASPNETCORE_ENVIRONMENT with some specific environment value ("live", "staging", "production", whatever). You can specify this variable in your project settings for your development environment, and of course you need to set it in your staging and production environments also. The way you do it there depends on what kind of environment this is.

UPDATE: I just realized you want to choose the appsettings.xxx.json based on your current build configuration. This cannot be achieved with my proposed solution and I don't know if there is a way to do this. The "environment variable" way, however, works and might as well be a good alternative to your approach.

Answer 2

You may use conditional compilation:

public Startup(IHostingEnvironment env)
{
    var builder = new ConfigurationBuilder()
    .SetBasePath(env.ContentRootPath)
    .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
#if SOME_BUILD_FLAG_A
    .AddJsonFile($"appsettings.flag_a.json", optional: true)
#else
    .AddJsonFile($"appsettings.no_flag_a.json", optional: true)
#endif
    .AddEnvironmentVariables();
    this.configuration = builder.Build();
}

Answer 3

Just an update for .NET core 2.0 users, you can specify application configuration after the call to CreateDefaultBuilder:

public class Program
{
   public static void Main(string[] args)
   {
      BuildWebHost(args).Run();
   }

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

   static void ConfigConfiguration(WebHostBuilderContext ctx, IConfigurationBuilder config)
   {
            config.SetBasePath(Directory.GetCurrentDirectory())
                .AddJsonFile("config.json", optional: false, reloadOnChange: true)
                .AddJsonFile($"config.{ctx.HostingEnvironment.EnvironmentName}.json", optional: true, reloadOnChange: true);

   }
 }

Answer 4

1.Create multiple appSettings.$(Configuration).jsons like appSettings.staging.json appSettings.production.json

2.Create a pre-build event on the project which copies the respective file to appSettings.json like this

copy appSettings.$(Configuration).json appSettings.json

3.Use Only appSettings.json in your Config Builder

var builder = new ConfigurationBuilder()
            .SetBasePath(env.ContentRootPath)
            .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
            .AddEnvironmentVariables();

        Configuration = builder.Build();

Answer 5

In ASP.NET Core you should rather use EnvironmentVariables instead of build configuration for proper appsettings.json

Right click on you project > Properties > Debug > Environment Variables

ASP.NET Core will take proper appsettings.json file.

Now you can use that Environment Variable like this:

    public Startup(IHostingEnvironment env)
    {
        var builder = new ConfigurationBuilder()
            .SetBasePath(env.ContentRootPath)
            .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
            .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true)
            .AddEnvironmentVariables();

        Configuration = builder.Build();
    }

If you do it @Dmitry 's way, you will have problems eg. when overriding appsettings.json values on Azure.

Answer 6

You can add the configuration name as the ASPNETCORE_ENVIRONMENT in the launchSettings.json as below

  "iisSettings": {
    "windowsAuthentication": false,
    "anonymousAuthentication": true,
    "iisExpress": {
      "applicationUrl": "http://localhost:58446/",
      "sslPort": 0
    }
  },
  "profiles": {
    "IIS Express": {
      "commandName": "IISExpress",
      "environmentVariables": {
        ASPNETCORE_ENVIRONMENT": "$(Configuration)"
      }
    }
  }