Hosting

Component: NServiceBus
NuGet Package NServiceBus (7.2 - 7.3)

At its core NServiceBus is a library; as such it can be hosted in any .NET process.

There are several approaches to hosting.

Microsoft Generic Host

The Microsoft Generic Host is the most common way to host NServiceBus on .NET Core. NServiceBus can be integrated easily wth the generic host using the NServiceBus.Extensions.Hosting package.

Self-hosting

"Self-hosting" is a general term used when the application code takes full control over all facets of hosting NServiceBus. This includes the following actions:

Override the default critical error callback when self-hosting NServiceBus. Refer to the Critical Errors article for more information.

When self-hosting, the user is responsible for creating and starting the endpoint instance:

var endpointConfiguration = new EndpointConfiguration("EndpointName");
// Apply other necessary endpoint configuration, e.g. transport
var startableEndpoint = await Endpoint.Create(endpointConfiguration)
    .ConfigureAwait(false);
var endpointInstance = await startableEndpoint.Start()
    .ConfigureAwait(false);

// Shortcut
var endpointInstance2 = await Endpoint.Start(endpointConfiguration)
    .ConfigureAwait(false);

The user is also responsible for properly shutting down the endpoint when it is no longer needed (usually when the application terminates).

await endpointInstance.Stop().ConfigureAwait(false);
The endpoint instance is not disposable due to the asynchronous nature of the pipeline. Call Stop in an async manner (see example above).

Windows Service hosting

A Windows Service is the most common way to host NServiceBus in Windows.

Related:

Docker container hosting

An endpoint can be hosted inside a Docker container.

Related:

Send-only hosting

A "Send-only endpoint" is used when the only purpose of the endpoint is to send messages and no message processing is required in that endpoint. Common use cases include websites, console applications, and windows applications. This is the code for starting an endpoint in send-only mode.

var endpointConfiguration = new EndpointConfiguration("EndpointName");
endpointConfiguration.SendOnly();
// Apply other necessary endpoint configuration, e.g. transport
var endpointInstance = await Endpoint.Start(endpointConfiguration)
    .ConfigureAwait(false);

The only configuration required when running in this mode is the destination when sending a message.

Web hosting

NServiceBus can be hosted in any web technology that supports .NET. See Web Application Hosting.

WebJob hosting

NServiceBus can be hosted in a WebJob. See Self-Hosting in Azure WebJobs

Service Fabric hosting

Service Fabric can be used to host NServiceBus endpoints in several ways. See Service Fabric Hosting.

Multi-hosting

"Multi-hosting" refers to hosting multiple NServiceBus endpoints in a single .NET process.

It is safe for multiple endpoints to share the same AppDomain or use multiple AppDomains.

Related:

Accessing the bus

Most usages of the bus will occur where the NServiceBus APIs are used, for example handlers and sagas. However, there are other scenarios that may require an alternate approach where the user needs to directly access the bus from outside of the framework.

Static variable

For many scenarios, dependency injection is not required. In these cases, a simple public static variable on the startup class will suffice. This variable can then be access globally in the application. For example:

  • In a Windows service or console the variable could be placed in Program.cs
  • In a website the variable could be placed in Global.asax.cs.

The static variable could also be placed in a helper class.

public static class EndpointInstance
{
    public static IEndpointInstance Endpoint { get; private set; }
    public static void SetInstance(IEndpointInstance endpoint)
    {
        if (Endpoint != null)
        {
            throw new Exception("Endpoint already set.");
        }
        Endpoint = endpoint;
    }
}

Custom hosting

A "Custom host" is a process or library that wraps the NServiceBus library to take partial control of configuration, startup and shutdown. This host exposes extension points for common activities and uses conventions and/or sensible defaults for many other configuration options.

ILMerging NServiceBus assemblies

Since NServiceBus makes assumptions on aspects like assembly names, ILMerging any of the NServiceBus* assemblies is not supported.

Hosting environment requirements

NServiceBus endpoints have certain requirements on the hosting environment:

  • The endpoint process needs write access to write log files. See the logging documentation for more details about the default log file location and how to configure logging.
  • The endpoint process needs write access to write the startup diagnostics file. See the startup diagnostics documentation for more details about the diagnostic file.

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