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Blazor hosting models

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Blazor currently has five hosting options:

  • Static Server Rendering
    Renders components to static HTML on the server with no SignalR circuit or client-side interactivity. Each navigation causes a full page load.

    dotnet new blazor --interactivity None -n MyApp

  • Interactive Server
    Runs .NET code on the server and communicates with the browser via a persistent SignalR connection. Enables rich interactivity with low client-side requirements.

    dotnet new blazor --interactivity Server -n MyApp

  • Interactive WebAssembly
    Downloads and runs .NET assemblies directly in the browser via WebAssembly. Can work offline and reduces server load, but has a slower initial load.

    dotnet new blazor --interactivity WebAssembly -n MyApp

  • Interactive Auto
    Starts with Interactive Server rendering, then downloads the .NET assemblies in the background and switches to WebAssembly mode on future visits.

    dotnet new blazor --interactivity Auto -n MyApp

  • Blazor Hybrid
    Hosts Blazor components inside a native .NET application (MAUI, WPF, WinForms) using the BlazorWebView control, with full access to native device APIs.

    dotnet new maui-blazor -n MyApp

The WebAssembly and Auto options add a .Client project to the solution that compiles to WebAssembly.

Server-side hosting was released in September 2019, WebAssembly was officially released in May 2020, Blazor Hybrid was introduced with .NET 6 in 2021, and .NET 8 unified the Blazor Web App template with multiple render modes.

Since .NET 8, the recommended approach is the Blazor Web App template, which supports all hosting models through render mode selection. Previously, developers had to choose between the blazorwasm and blazorserver project templates at creation time. Now the same project can mix multiple render modes on a per-component or per-page basis.

Visual Studio

Create a new project, search for Blazor, and select the Blazor Web App template. In the Additional information dialog, choose an Interactive render mode from the dropdown:

  • None - Static SSR only (no interactivity)
  • Server - Interactive Server as the default render mode
  • WebAssembly - Interactive WebAssembly as the default render mode
  • Auto - Interactive Auto (Server first, WebAssembly after download)

Command line

dotnet new blazor --interactivity <None|Server|WebAssembly|Auto> -n MyApp

Use --all-interactive to make every page interactive by default instead of using per-page/component @rendermode directives.

Render mode nesting rules

Interactive render modes can be combined within a single page, but there is an important constraint: a component cannot have a lower interactivity level than its parent. Mixing Server and WebAssembly components on one page must be done from a static SSR parent, not from an interactive one. Specifically:

  • Interactive Server and Interactive WebAssembly components can be embedded in a static page (the parent is static SSR).
  • Interactive WebAssembly components cannot be embedded inside an Interactive Server component, because that would require the signal to cross from the server circuit to the client without a bridge.
  • Interactive Server components cannot be embedded inside an Interactive WebAssembly component, because WebAssembly mode has no SignalR circuit to the server.

Blazor WebAssembly

Pros

Blazor WebAssembly runs on the client, inside the browser, so it can be deployed as static files. Despite this, Blazor WebAssembly apps will not run directly from the local file system due to browser security restrictions.

Blazor WebAssembly can work off-line. When the network connection to the server is lost, the client app can continue to function (obviously it won't be able to talk to the server to retrieve new data).

It can also quite easily run as a Progressive Web App, which means the client can choose to install our app onto their device and run it whenever they wish without any network access at all.

With code running on the client's machine it means the server load is significantly reduced.

Cons

The blazor.webassembly.js file bootstraps the client application. It downloads the .NET runtime and all required assemblies, which makes the start-up time slower than server-side rendering the first time the app runs. Since .NET 8, assemblies ship as Webcil-packaged .wasm files that use standard HTTP caching, so subsequent visits are significantly faster. AOT compilation (available since .NET 6) improves runtime performance at the cost of a larger initial download.

Static Server Rendering

Static Server Rendering (also called Static SSR) renders components to static HTML on the server. There is no SignalR circuit, no Blazor .js file downloaded by the browser, and no client-side interactivity. Each navigation or form submission causes a full page load from the server.

Static SSR is the default when creating a Blazor Web App with --interactivity None, or when a component does not specify an interactive render mode.

Pros

  • Fastest initial page load - HTML is rendered on the server and sent directly to the browser.
  • Best search engine optimisation - all content is present in the initial HTML.
  • Lowest server resource usage per request - no persistent SignalR connections to maintain.
  • Works on any browser.

Cons

  • No client-side interactivity or UI event handling.
  • Full page reloads on navigation and form submissions (unless enhanced navigation is enabled).

Interactive Server

Pros

Interactive Server pre-renders HTML content before it is sent to the client's browser. This makes it search-engine friendly, and there is no perceivable start-up time after the SignalR connection is established. Note that prerendering is on by default for all interactive render modes (including WebAssembly and Auto), not just Interactive Server. It can be disabled per component using @rendermode="new InteractiveServerRenderMode(prerender: false)".

Cons

Interactive Server sets up an in-memory session for the current client and uses SignalR to communicate between the .NET running on the server and the client's browser. All memory and CPU usage comes at a cost to the server, for all users. It also requires session affinity (sticky sessions) or the Azure SignalR Service when load-balancing.

Once the initial page has been rendered and sent to the browser, the blazor.web.js file hooks into any relevant user interaction events in the browser so it can mediate between the user and the server. For example, if a rendered element has an @onclick event registered, blazor.web.js will hook into its JavaScript onclick event and then use its SignalR connection to send that event to the server and execute the relevant .NET code.

<p>
  Current count = @currentCount
</p>
<button @onclick=IncrementCount>Click me</button>

@code
{
  private int currentCount;

  private void IncrementCount()
  {
    currentCount++;
  }
}

After the .NET code has finished, the server will re-render the components on the page and then send a delta package of HTML back to the client's browser so it can update its display without having to reload the entire page.

Note: Render trees are covered in depth later.

If we run a standard Blazor app, click the Counter link in the menu, and then click the Click me button we can observe the SignalR data communication to and from the server.

  1. Run the app in the Chrome browser.
  2. Click the Counter link in the app's menu.
  3. Press F12 to open the browser's Developer tools.
  4. In the developer tools window, click the Network tab.
  5. Reload the page.
  6. Next, click the WS tab (short for WebSocket).
  7. Click on the _blazor item to show socket data.
  8. Clicking the Click me button will show network traffic something like the following (abridged and formatted for easy reading).
DispatchBrowserEvent
  {
    "browserRendererId": 0,
    "eventHandlerId": 3,
    "eventArgsType": "mouse",
    "eventFieldInfo": null
  }
  {
    "type": "click",
    "detail": 1,
    "screenX": 338,
    "screenY": 211,
    "clientX": 338,
    "clientY": 109,
    "button": 0,
    "buttons": 0,
    "ctrlKey": false,
    "shiftKey": false,
    "altKey": false,
    "metaKey": false
  }

Which results in a response from the server that looks something like the following:

Note: The highlighted 1 indicates the delta HTML, and is the new value for the counter.

This round-trip can provide a sluggish experience if the client's browser and the server are not close or the network connection between them is slow, especially when the events triggering state change are frequent. For example, an event such as onmousemove will fire very often.

Additionally, changes that require large HTML delta updates can also be slow. For example, if we were to have an HTML <textarea> component in our page that updated an area of the display to preview the user's input as they type, the delta HTML from the server would increase with each character added to the <textarea>. When the input content becomes large, it results in a large network transfer for every keypress.

Unlike Blazor WebAssembly, once the connection from the browser to the server is lost the app becomes unresponsive. Blazor will try to re-establish a connection to the server. Since .NET 10, the template includes a customizable ReconnectModal component that shows connection status, and circuit state can be persisted across disconnects to preserve the user's session state.

Blazor Hybrid

Blazor Hybrid lets you host Blazor components inside a native .NET application using the BlazorWebView control. The UI is rendered as HTML and CSS inside an embedded WebView (WKWebView on iOS, Android WebView, WebView2 on Windows), while your .NET code runs natively on the device with full access to device APIs such as the camera, GPS, file system, and notifications. There is no WebAssembly runtime and no HTTP server involved.

Blazor Hybrid is supported on:

  • .NET MAUI - cross-platform mobile and desktop (iOS, Android, Windows, macOS, iPadOS)
  • WPF - Windows desktop applications
  • Windows Forms - Windows desktop applications

For .NET MAUI, the project template is dotnet new maui-blazor or select .NET MAUI Blazor App in Visual Studio.

Pros

  • Native performance and full access to device APIs.
  • Share the same Blazor components across web and native apps.
  • Works offline - no server connection required.
  • Can be published to app stores (Apple App Store, Google Play, Microsoft Store).

Cons

  • Larger application binary size compared to a web app.
  • Platform-specific deployment - must build and distribute per-platform packages.
  • Cannot run in a browser - it is a native application.

Choosing a render mode

The --interactivity flag on dotnet new blazor sets the default render mode for the entire project, but render modes can be applied per-component or per-page using the @rendermode directive. This allows you to mix interactivity types within a single application.

For example, a public-facing marketing site can use Static Server Rendering for most pages while using Interactive Server or Interactive WebAssembly for an admin dashboard or a real-time data page.

For a detailed look at each render mode, see the Render modes section.