Integrating C# Logic with Camunda Workflows: A Comprehensive Guide

Introduction

Camunda is a powerful, open-source workflow and decision automation platform designed to orchestrate processes. While it natively supports Java for scripting and execution, there are scenarios where integrating with other languages like C# becomes essential, especially in environments heavily invested in .NET. This blog post will walk you through the process of incorporating C# logic into Camunda workflows, leveraging REST APIs, and external task patterns.

Why Integrate C# with Camunda?

Organizations might choose to integrate C# with Camunda for several reasons:

• Existing .NET Infrastructure: Many enterprises have significant investments in .NET infrastructure, making it beneficial to reuse existing C# libraries and business logic.
• Skill Sets: Teams may have more expertise in C#, necessitating the need to integrate it into their workflow solutions.
• Performance and Security: Certain performance-critical or security-sensitive components might already be developed in C#.

Overview of the Integration Approach

To integrate C# logic within Camunda, we will use the following components:

1. Camunda BPMN Engine: To design and manage workflows.
2. External Task Pattern: To allow C# applications to fetch and complete tasks from the workflow.
3. REST API: For communication between Camunda and the C# application.

Setting Up Camunda

First, ensure you have a running instance of Camunda. You can download it from the Camunda official website.

Designing the BPMN Workflow

1. Create a BPMN Model:
   Use the Camunda Modeler to create a BPMN diagram. Include an external task that will be handled by the C# application.

   <bpmn:serviceTask id="ServiceTask_1" name="Call C# Service" camunda:type="external" camunda:topic="csharpTopic">
     <bpmn:extensionElements>
       <camunda:properties>
         <camunda:property name="serviceUrl" value="http://localhost:5000/api/execute"/>
       </camunda:properties>
     </bpmn:extensionElements>
   </bpmn:serviceTask>

2. Deploy the BPMN Model:
   Deploy the BPMN model to the Camunda engine using the REST API or through the Camunda Cockpit.

Setting Up the C# Application

1. Create a .NET Core Application:
   Use the .NET CLI or Visual Studio to create a new ASP.NET Core Web API project.

   dotnet new webapi -n CamundaCSharpIntegration
   cd CamundaCSharpIntegration

2. Install Necessary Packages:
   Install RestSharp for handling HTTP requests and responses.

   dotnet add package RestSharp

3. Implement the Camunda Client:
   Create a service to interact with the Camunda REST API.

   using RestSharp;
   using System;
   using System.Threading.Tasks;

   public class CamundaClient
   {
       private readonly RestClient _client;

       public CamundaClient(string baseUrl)
       {
           _client = new RestClient(baseUrl);
       }

       public async Task FetchAndCompleteTaskAsync()
       {
           var request = new RestRequest("external-task/fetchAndLock", Method.POST);
           request.AddJsonBody(new
           {
               workerId = "csharpWorker",
               maxTasks = 1,
               topics = new[]
               {
                   new { topicName = "csharpTopic", lockDuration = 10000 }
               }
           });

           var response = await _client.ExecuteAsync<ExternalTaskResponse[]>(request);
           if (response.Data.Length > 0)
           {
               var task = response.Data[0];
               Console.WriteLine($"Fetched task {task.Id}");

               // Execute business logic here
               var result = ExecuteBusinessLogic(task.Variables);

               // Complete the task
               var completeRequest = new RestRequest($"external-task/{task.Id}/complete", Method.POST);
               completeRequest.AddJsonBody(new
               {
                   workerId = "csharpWorker",
                   variables = new
                   {
                       result = new { value = result }
                   }
               });
               await _client.ExecuteAsync(completeRequest);
               Console.WriteLine($"Completed task {task.Id}");
           }
       }

       private string ExecuteBusinessLogic(dynamic variables)
       {
           // Implement your C# business logic here
           return "result from C# logic";
       }
   }

   public class ExternalTaskResponse
   {
       public string Id { get; set; }
       public dynamic Variables { get; set; }
   }

4. Run the C# Application:
   Ensure your application is running and capable of fetching and completing tasks.

   dotnet run

Configuring the Camunda Workflow to Use the C# Service

1. Set Up Task Fetching:
   Configure the Camunda BPMN workflow to use the csharpWorker for tasks related to csharpTopic.
2. Trigger the Workflow:
   Use the Camunda REST API to start a process instance.

   curl -X POST "http://localhost:8080/engine-rest/process-definition/key/yourProcessDefinitionKey/start"

3. Monitor the Workflow:
   Monitor the workflow execution in the Camunda Cockpit. You should see the tasks being fetched and completed by the C# application.

Conclusion

Integrating C# logic with Camunda workflows enables organizations to leverage their existing .NET investments while benefiting from Camunda’s powerful workflow capabilities. By using the external task pattern and REST APIs, we can seamlessly connect C# applications with Camunda, ensuring a robust and flexible workflow automation solution.

This guide provides a foundational approach to achieve this integration. Depending on your specific requirements, you may need to expand on this by adding error handling, security, and scalability considerations. Happy coding!