Configuring multiple ASP.NET Core hosting environment

The hosting environment is used to indicate at runtime on which environment an ASP.NET Core application is running. There can be multiple values for ASP.NET Core Hosting Environment and it can be set any single value. Framework provided environments are Development, Staging & Production but you can specify your own values as well i.e. Testing, QA, PrePROD, etc.

Environment variables allow the application to be configured as per the environment on which the application is running.

Why hosting environments?

As part of the software development life cycle, an application has to go through various phases like Development, Testing & Production. We as application developers need to configurable different parameters for different environments like each environment will have its own database, different versions (URL) of third party services, different application features like logging, bundling, minification, exception handling, etc based on the environment on which application is running.

Multiple environments let us control these parameters at runtime i.e database connections, third party service URLs, application behavior like logging, exception, bundling, etc can be configured environment wise.

How to set ASP.NET Core hosting environment

There are a number of ways to set the hosting environment variable. This environment variable needs to be set on each machine on which the application is required to run.

using windows command line

To set the environment variable from command prompt following command can be used. This is applicable for the current session and app should be started using dotnet run command.

set ASPNETCORE_ENVIRONMENT=Staging
dotnet run --no-launch-profile
using PowerShell
$Env:ASPNETCORE_ENVIRONMENT = "Staging"
dotnet run --no-launch-profile

Both command line & PowerShell sets environment variables only for the processes launched from that command window.

using windows environment variables

To set ASP.NET Core hosting environment variable globally in windows so that each you don’t need to set it before running the application use windows environment variables

To set environment variable globally open Control Panel ==> System ==> Advanced System Settings ==> Environment Variables ==> System Variable New/Edit & set values in ‘name’ and ‘value’ and click ok

ASP.NET Core Hosting Environment
using web.config

Environment variable can be set in web.config as well. Environment variable can be specified for the process in the processPath attribute in web.config. Environment variables set in this section takes precedence over system environment variables.

<aspNetCore processPath="dotnet"
      arguments=".\MyApp.dll"
      stdoutLogEnabled="false"
      stdoutLogFile=".\logs\stdout"
      hostingModel="inprocess">
  <environmentVariables>
    <environmentVariable name="ASPNETCORE_ENVIRONMENT" value="Development" />
  </environmentVariables>
</aspNetCore>

Developers can use this to temporarily set the environment to development for debugging purpose.

using Per IIS Application Pool

Environment variable can also be set at IIS pool level for an application running in an isolated application pool. When ASPNETCORE_ENVIRONMENT is set for an app pool, its value overrides a setting at the system level.

<applicationPools>
   <add name="CorePool" managedRuntimeVersion="v4.0" managedPipelineMode="Classic">
      <environmentVariables>
         <add name="ASPNETCORE_ENVIRONMENT" value="Staging" />
      </environmentVariables>
   </add>
</applicationPools>

AppCmd.exe can be used to add environment variables to the IIS pool level.

appcmd.exe set config -section:system.applicationHost/applicationPools /+"[name='CorePool'].environmentVariables.[name='ASPNETCORE_ENVIRONMENT',value='Staging']" /commit:apphost

Restart IIS or Server after setting the environment variable in IIS for application to have new values available after changes.

How to use ASP.NET Core hosting environment in your application

Environment based startup class

Below is the example of environment based startup class in which IWebHostingEnvironment has been injected to identify the environment and add code behavior accordingly.

public class Startup
{
    public Startup(IConfiguration configuration, IWebHostEnvironment env)
    {
        Configuration = configuration;

        var builder = new ConfigurationBuilder()
            .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true);
    }

    //Remaining code was removed

    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }
        else
        {
            app.UseExceptionHandler("/Home/Error");
        }
        app.UseStaticFiles();

        app.UseRouting();

        //Remaining code was removed
    }
}

In the above code in startup constructor environment variable name has been used to load appsettings.json file based on the environment configured for application i.e. appsettings.development.json or appsettings.production.json file will be used based on the environment set at runtime.

Also in the configure method different application behavior has been set for exception handling based on the environment set at runtime.

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How to add custom ASP.NET Core hosting environment

Development, Staging & Production environments are provided by default by the framework. But ASPNETCORE_ENVIRONMENT can be set to any string value. To configure your own environments following extension class can be added.

public static class HostingEnvironmentExtensions
{
    public const string QAEnvironment = "QA";
    public const string UATEnvironment = "UAT";
    public const string TestEnvironment = "Test";

    public static bool IsQA(this IWebHostEnvironment hostingEnvironment)
    {
        return hostingEnvironment.IsEnvironment(QAEnvironment);
    }

    public static bool IsUAT(this IWebHostEnvironment hostingEnvironment)
    {
        return hostingEnvironment.IsEnvironment(UATEnvironment);
    }

    public static bool IsTest(this IWebHostEnvironment hostingEnvironment)
    {
        return hostingEnvironment.IsEnvironment(TestEnvironment);
    }
}

Once configured it will be available under environment variable as shown below

ASP.NET Core Custom Environments

Summary

ASP.NET Core hosting environment allows developers to control how their application will behave in different environments. There are multiple ways available to set an environment variable for the application.

ASP.NET Core hosting has provided 3 environments i.e. development, staging & production by default but custom environments can be added and practically any string can be used for environment name.

References: https://docs.microsoft.com/en-us/aspnet/core/fundamentals/environments?view=aspnetcore-3.1

You can also check my other Article on ASP.NET Core bundling & minification: https://procodeguide.com/programming/asp-net-core-bundling-minification/

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