Elsa Web

In this guide, we'll demonstrate how to integrate Elsa Workflows into an ASP.NET Core application. This setup is ideal for executing long-running workflows in the background, supporting various activities like Timer, Cron, Event, and others that necessitate a background service.

Initial Setup

Create a new empty ASP.NET app using the following command:

dotnet new web -n "ElsaWeb" -f net8.0

Navigate to your project's root directory and install the Elsa package:

cd ElsaWeb
dotnet add package Elsa

Open the Program.cs file and replace its contents with:

Program.cs:

using Elsa.Extensions;

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
builder.Services.AddControllers();
builder.Services.AddElsa();

var app = builder.Build();

// Configure the HTTP request pipeline.
app.UseHttpsRedirection();
app.UseAuthorization();
app.MapControllers();
app.Run();

This configuration allows your application to use Elsa services for running workflows.

Trying it out

Example 1: Console Output

Add a new controller named RunWorkflowController:

Controllers/RunWorkflowController.cs:

using Elsa.Workflows.Activities;
using Elsa.Workflows.Contracts;
using Microsoft.AspNetCore.Mvc;

namespace ElsaWeb.Controllers;

[ApiController]
[Route("run-workflow")]
public class RunWorkflowController(IWorkflowRunner workflowRunner) : ControllerBase
{
    [HttpGet]
    public async Task Get()
    {
        await workflowRunner.RunAsync(new WriteLine("Hello ASP.NET world!"));
    }
}

Start the application using the following command:

dotnet run --urls=https://localhost:5001

Then visit https://localhost:5001/run-workflow in your browser. The console should display "Hello ASP.NET world!"

Example 2: HTTP Response

Install the Elsa.Http Package

dotnet add package Elsa.Http

Modify the Elsa setup in Program.cs:

builder.Services.AddElsa(elsa => elsa.UseHttp());

Adjust the controller to use the WriteHttpResponse activity:

Controllers/RunWorkflowController.cs:

using Elsa.Http;
using Elsa.Workflows.Contracts;
using Microsoft.AspNetCore.Mvc;

namespace ElsaWeb.Controllers;

[ApiController]
[Route("run-workflow")]
public class RunWorkflowController(IWorkflowRunner workflowRunner) : ControllerBase
{
    [HttpGet]
    public async Task Get()
    {
        await workflowRunner.RunAsync(new WriteHttpResponse
        {
            Content = new("Hello ASP.NET world!")
        });
    }
}

Restart your app and navigate to https://localhost:5001/run-workflow. The browser should now display the message.

Example 3: Workflows as HTTP Endpoints

In addition to programmatically invoking workflows, you can also create workflows that themselves are routable via HTTP. To enable this, we need to add the WorkflowsMiddleware ASP.NET middleware component to the request pipeline.

In Program.cs, add the following line before app.Run();:

app.UseWorkflows();

Create a new workflow class with HTTP capabilities:

Workflows/HttpHelloWorld.cs:

using Elsa.Http;
using Elsa.Workflows;
using Elsa.Workflows.Activities;
using Elsa.Workflows.Contracts;

namespace ElsaWeb.Workflows;

public class HttpHelloWorld : WorkflowBase
{
    protected override void Build(IWorkflowBuilder builder)
    {
        builder.Root = new Sequence
        {
            Activities =
            {
                new HttpEndpoint
                {
                    Path = new("/hello-world"),
                    CanStartWorkflow = true
                },
                new WriteHttpResponse
                {
                    Content = new("Hello world of HTTP workflows!")
                }
            }
        };
    }
}

Update Program.cs to register this workflow:

using ElsaWeb.Workflows; // Add this line.

builder.Services.AddElsa(elsa =>
{
    elsa.AddWorkflow<HttpHelloWorld>();
    elsa.UseHttp();
});

Restart the app and visit https://localhost:5001/workflows/hello-world. You should see the corresponding message.

Summary

We've covered how to set up Elsa Workflows in an ASP.NET Core application, demonstrating various methods of workflow execution and integration. This approach allows for versatile and efficient handling of background processes and activities within your ASP.NET applications.

The complete code and additional resources are available here.