Details: https://docs.microsoft.com/en-us/aspnet/core/fundamentals/environments

ASPNETCORE_ENVIRONMENT variable

• ASPNETCORE_ENVIRONMENT is an environment variable that can be set in project Properties & launchSettings.json
• ASP.NET Core reads ASPNETCORE_ENVIRONMENT at app startup (and stores the value in IHostingEnvironment.EnvironmentName)
• you can set ASPNETCORE_ENVIRONMENT to any value
• if ASPNETCORE_ENVIRONMENT isn’t set, it defaults to ‘Production’
• values provided by aspnet core: ‘Development’, ‘Production’ & ‘Staging’

Setting environment variable

1. Project properties

• right click on project > properties > Debug > Environment variables
• Name: ASPNETCORE_ENVIRONMENT, Value: Foo

2. launchSettings
Solution explorer > Show all files > Properties > launchSettings.json

  "profiles": {
    "IIS Express": {
      
	  // ... ... ...
	  
      "environmentVariables": {
        "ASPNETCORE_ENVIRONMENT": "Development"
      }
    }
    

Notes:

• launchSettings.json overrides value of ASPNETCORE_ENVIRONMENT from project properties
• you must restart VS after changing launchSettings.json

Multiple appsettings json

• default: appsettings.json
• depending on the value of ASPNETCORE_ENVIRONMENT, appsettings.X.json will be used

appsettings for corresponding environment

ExceptionHandler depending on environment

Startup.cs

  public void Configure(IApplicationBuilder app, IHostingEnvironment env)
  {
      if (env.IsDevelopment())
      {
          app.UseDeveloperExceptionPage();
      }

      if (env.IsProduction() || env.IsStaging() || env.IsEnvironment("Staging_2"))
      {
          app.UseExceptionHandler("/Error");
      }
      
      // ... ... ...
  }