ASP.NET Core Blazor environments

This article explains how to configure and read the environment in a Blazor app.

When running an app locally, the environment defaults to Development. When the app is published, the environment defaults to Production.

We recommend the following conventions:

• Always use the "Development" environment name for local development. This is because the ASP.NET Core framework expects exactly that name when configuring the app and tooling for local development runs of an app.

• For testing, staging, and production environments, always publish and deploy the app. You can use any environment naming scheme that you wish for published apps, but always use app setting file names with casing of the environment segment that exactly matches the environment name. For staging, use "Staging" (capital "S") as the environment name, and name the app settings file to match (appsettings.Staging.json). For production, use "Production" (capital "P") as the environment name, and name the app settings file to match (appsettings.Production.json).

Set the environment

The environment is set using any of the following approaches:

• Blazor Web App: Use any of the approaches described in Use multiple environments in ASP.NET Core for general ASP.NET Core apps.
• Blazor Web App or standalone Blazor WebAssembly: Blazor start configuration
• Standalone Blazor WebAssembly: Blazor-Environment header
• Blazor Web App or standalone Blazor WebAssembly: Azure App Service

On the client for a Blazor Web App, the environment is determined from the server via a middleware that communicates the environment to the browser via a header named Blazor-Environment. The header sets the environment when the WebAssemblyHost is created in the client-side Program file (WebAssemblyHostBuilder.CreateDefault).

For a standalone Blazor WebAssembly app running locally, the development server adds the Blazor-Environment header with the environment name obtained from the hosting environment. The hosting environment sets the environment from the ASPNETCORE_ENVIRONMENT environment variable established by the project's Properties/launchSettings.json file. The default value of the environment variable in a project created from the Blazor WebAssembly project template is Development. For more information, see the Set the client-side environment via header section.

For app's running locally in development, the app defaults to the Development environment. Publishing the app defaults the environment to Production.

Set the client-side environment via Blazor startup configuration

The following example starts Blazor in the Staging environment if the hostname includes localhost. Otherwise, the environment is set to its default value.

Blazor Web App:

<script src="{BLAZOR SCRIPT}" autostart="false"></script>
<script>
  if (window.location.hostname.includes("localhost")) {
    Blazor.start({
      webAssembly: {
        environment: "Staging"
      }
    });
  } else {
    Blazor.start();
  }
</script>

In the preceding example, the {BLAZOR SCRIPT} placeholder is the Blazor script path and file name. For the location of the script, see ASP.NET Core Blazor project structure.

Note

For Blazor Web Apps that set the webAssembly > environment property in Blazor.start configuration, it's wise to match the server-side environment to the environment set on the environment property. Otherwise, prerendering on the server will operate under a different environment than rendering on the client, which results in arbitrary effects. For general guidance on setting the environment for a Blazor Web App, see Use multiple environments in ASP.NET Core.

Standalone Blazor WebAssembly:

<script src="{BLAZOR SCRIPT}" autostart="false"></script>
<script>
  if (window.location.hostname.includes("localhost")) {
    Blazor.start({
      environment: "Staging"
    });
  } else {
    Blazor.start();
  }
</script>

In the preceding example, the {BLAZOR SCRIPT} placeholder is the Blazor script path and file name. For the location of the script, see ASP.NET Core Blazor project structure.

Using the environment property overrides the environment set by the Blazor-Environment header.

The preceding approach sets the client's environment without changing the Blazor-Environment header's value, nor does it change the server project's console logging of the startup environment for a Blazor Web App that has adopted global Interactive WebAssembly rendering.

To log the environment to the console in either a standalone Blazor WebAssembly project or the .Client project of a Blazor Web App, place the following C# code in the Program file after the WebAssemblyHost is created with WebAssemblyHostBuilder.CreateDefault and before the line that builds and runs the project (await builder.Build().RunAsync();):

Console.WriteLine(
    $"Client Hosting Environment: {builder.HostEnvironment.Environment}");

For more information on Blazor startup, see ASP.NET Core Blazor startup.

Set the client-side environment via header

Blazor WebAssembly apps can set the environment with the Blazor-Environment header. Specifically, the response header must be set on the _framework/blazor.boot.json file, but there's no harm setting the header on file server responses for other Blazor file requests or the entire Blazor deployment.

Although the Blazor framework issues the header name in kebab case with mixed letter case (Blazor-Environment), you're welcome to use all-lower or all-upper kebab case (blazor-environment, BLAZOR-ENVIRONMENT).

For local development runs with Blazor's built-in development server, you can control the value of the Blazor-Environment header by setting the value of the ASPNETCORE_ENVIRONMENT environment variable in the project's Properties/launchSettings.json file. When running locally with the development server, the order of precedence for determining the app's environment is Blazor.start configuration (environment key) > Blazor-Environment response header (blazor.boot.json file) > ASPNETCORE_ENVIRONMENT environment variable (launchSettings.json). You can't use the ASPNETCORE_ENVIRONMENT environment variable (launchSettings.json) approach for a deployed Blazor WebAssembly app. The technique only works with the development server on local runs of the app.

IIS

In the following example for IIS, the custom header (Blazor-Environment) is added to the published web.config file. The web.config file is located in the bin/Release/{TARGET FRAMEWORK}/publish folder, where the {TARGET FRAMEWORK} placeholder is the target framework:

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
  <system.webServer>
    ...
    <httpProtocol>
      <customHeaders>
        <add name="Blazor-Environment" value="Staging" />
      </customHeaders>
    </httpProtocol>
  </system.webServer>
</configuration>

Note

To use a custom web.config file for IIS that isn't overwritten when the app is published to the publish folder, see Host and deploy ASP.NET Core Blazor WebAssembly.

Nginx

For Nginx servers, use the add_header directive from the ngx_http_headers_module:

http {
    server {
        ...
        location / {
            ...
            add_header Blazor-Environment "Staging";
        }
    }
}

For more information, see the following resources:

• Nginx documentation
• Blazor WebAssembly Nginx hosting guidance

Apache

For Apache servers, use the Header directive from the mod_headers module:

<VirtualHost *:80>
    ...
    Header set Blazor-Environment "Staging"
    ...
</VirtualHost>

For more information:

• Apache documentation (search the latest release for "mod_headers")
• Blazor WebAssembly Apache hosting guidance

Set the environment for Azure App Service

For a standalone Blazor WebAssembly app, you can set the environment manually via start configuration or the Blazor-Environment header.

For a server-side app, set the environment via an ASPNETCORE_ENVIRONMENT app setting in Azure:

1. Confirm that the casing of environment segments in app settings file names match their environment name casing exactly. For example, the matching app settings file name for the Staging environment is appsettings.Staging.json. If the file name is appsettings.staging.json (lowercase "s"), the file isn't located, and the settings in the file aren't used in the Staging environment.

2. For Visual Studio deployment, confirm that the app is deployed to the correct deployment slot. For an app named BlazorAzureAppSample, the app is deployed to the Staging deployment slot.

3. In the Azure portal for the environment's deployment slot, set the environment with the ASPNETCORE_ENVIRONMENT app setting. For an app named BlazorAzureAppSample, the staging App Service Slot is named BlazorAzureAppSample/Staging. For the Staging slot's configuration, create an app setting for ASPNETCORE_ENVIRONMENT with a value of Staging. Deployment slot setting is enabled for the setting.

When requested in a browser, the BlazorAzureAppSample/Staging app loads in the Staging environment at https://blazorazureappsample-staging.azurewebsites.net.

When the app is loaded in the browser, the response header collection for blazor.boot.json indicates that the Blazor-Environment header value is Staging.

App settings from the appsettings.{ENVIRONMENT}.json file are loaded by the app, where the {ENVIRONMENT} placeholder is the app's environment. In the preceding example, settings from the appsettings.Staging.json file are loaded.

Read the environment in a Blazor WebAssembly app

Obtain the app's environment in a component by injecting IWebAssemblyHostEnvironment and reading the Environment property.

ReadEnvironment.razor:

@page "/read-environment"
@using Microsoft.AspNetCore.Components.WebAssembly.Hosting
@inject IWebAssemblyHostEnvironment Env

<h1>Environment example</h1>

<p>Environment: @Env.Environment</p>

Read the environment client-side in a Blazor Web App

Assuming that prerendering isn't disabled for a component or the app, a component in the .Client project is prerendered on the server. Because the server doesn't have a registered IWebAssemblyHostEnvironment service, it isn't possible to inject the service and use the service implementation's host environment extension methods and properties during server prerendering. Injecting the service into an Interactive WebAssembly or Interactive Auto component results in the following runtime error:

There is no registered service of type 'Microsoft.AspNetCore.Components.WebAssembly.Hosting.IWebAssemblyHostEnvironment'.

To address this, create a custom service implementation for IWebAssemblyHostEnvironment on the server. Add the following class to the server project.

ServerHostEnvironment.cs:

using Microsoft.AspNetCore.Components.WebAssembly.Hosting;
using Microsoft.AspNetCore.Components;

public class ServerHostEnvironment(IWebHostEnvironment env, NavigationManager nav) : 
    IWebAssemblyHostEnvironment
{
    public string Environment => env.EnvironmentName;
    public string BaseAddress => nav.BaseUri;
}

In the server project's Program file, register the service:

builder.Services.TryAddScoped<IWebAssemblyHostEnvironment, ServerHostEnvironment>();

At this point, the IWebAssemblyHostEnvironment service can be injected into an interactive WebAssembly or interactive Auto component and used as shown in the Read the environment in a Blazor WebAssembly app section.

The preceding example can demonstrate that it's possible to have a different server environment than client environment, which isn't recommended and may lead to arbitrary results. When setting the environment in a Blazor Web App, it's best to match server and .Client project environments. Consider the following scenario in a test app:

• Implement the client-side (webassembly) environment property with the Staging environment via Blazor.start. See the Set the client-side environment via startup configuration section for an example.
• Don't change the server-side Properties/launchSettings.json file. Leave the environmentVariables section with the ASPNETCORE_ENVIRONMENT environment variable set to Development.

You can see the value of the IWebAssemblyHostEnvironment.Environment property change in the UI.

When prerendering occurs on the server, the component is rendered in the Development environment:

Environment: Development

When the component is rerendered just a second or two later, after the Blazor bundle is downloaded and the .NET WebAssembly runtime activates, the values change to reflect that the client is operating in the Staging environment on the client:

Environment: Staging

The preceding example demonstrates why we recommend setting the server environment to match the client environment for development, testing, and production deployments.

For more information, see the Client-side services fail to resolve during prerendering section of the Render modes article, which appears later in the Blazor documentation.

Read the client-side environment during startup

During startup, the WebAssemblyHostBuilder exposes the IWebAssemblyHostEnvironment through the HostEnvironment property, which enables environment-specific logic in host builder code.

In the Program file:

if (builder.HostEnvironment.Environment == "Custom")
{
    ...
};

The following convenience extension methods provided through WebAssemblyHostEnvironmentExtensions permit checking the current environment for Development, Production, Staging, and custom environment names:

• IsDevelopment
• IsProduction
• IsStaging
• IsEnvironment

In the Program file:

if (builder.HostEnvironment.IsStaging())
{
    ...
};

if (builder.HostEnvironment.IsEnvironment("Custom"))
{
    ...
};

The IWebAssemblyHostEnvironment.BaseAddress property can be used during startup when the NavigationManager service isn't available.

Additional resources

• ASP.NET Core Blazor startup
• Use multiple environments in ASP.NET Core
• Blazor samples GitHub repository (dotnet/blazor-samples) (how to download)