Workflows

Workflows are orchestrated sequences of operations that coordinate multiple services and components to achieve complex business objectives. They provide a declarative way to define, execute, and monitor multi-step processes while handling failures, retries, and compensating actions.

Core Responsibilities

Process Orchestration

• Multi-Service Coordination: Coordinate operations across multiple microservices
• State Management: Maintain workflow state throughout execution lifecycle
• Decision Logic: Implement conditional branching and parallel execution paths
• Error Handling: Manage failures with retry policies and compensation strategies

Business Process Management

• Long-Running Processes: Support workflows that span minutes to months
• Human Tasks: Integrate manual approval steps and user interactions
• Event-Driven Execution: React to external events and triggers
• Process Monitoring: Provide visibility into workflow execution and performance

Architecture Patterns

Saga Pattern

Use Cases:

• Distributed transactions across microservices
• Order processing with inventory, payment, and shipping
• User registration with multiple validation steps

State Machine Pattern

interface WorkflowState {
  current: string;
  data: Record<string, any>;
  transitions: Record<string, string[]>;
}

const orderWorkflow = {
  states: ['pending', 'validated', 'paid', 'shipped', 'delivered'],
  transitions: {
    pending: ['validated', 'cancelled'],
    validated: ['paid', 'cancelled'],
    paid: ['shipped', 'refunded'],
    shipped: ['delivered', 'returned'],
    delivered: ['completed']
  }
};

Implementation Technologies

Temporal Workflow Engine

import { workflow, activity } from '@temporalio/workflow';

@workflow.defn()
export class OrderProcessingWorkflow {
  @workflow.handler()
  async execute(order: Order): Promise<OrderResult> {
    // Validate inventory
    await workflow.executeActivity(validateInventory, order.items);
    
    // Process payment
    const payment = await workflow.executeActivity(processPayment, order.payment);
    
    // Ship order
    const shipment = await workflow.executeActivity(shipOrder, {
      orderId: order.id,
      paymentId: payment.id
    });
    
    return { orderId: order.id, shipmentId: shipment.id };
  }
}

Zeebe/Camunda BPMN

<?xml version="1.0" encoding="UTF-8"?>
<bpmn:definitions xmlns:bpmn="http://www.omg.org/spec/BPMN/20100524/MODEL">
  <bpmn:process id="order-process" isExecutable="true">
    <bpmn:startEvent id="order-received" />
    <bpmn:serviceTask id="validate-order" name="Validate Order" />
    <bpmn:serviceTask id="process-payment" name="Process Payment" />
    <bpmn:serviceTask id="ship-order" name="Ship Order" />
    <bpmn:endEvent id="order-completed" />
  </bpmn:process>
</bpmn:definitions>

Workflow Types

Synchronous Workflows

• Request-Response: Immediate execution with real-time response
• API Orchestration: Coordinate multiple API calls for single request
• Data Transformation: Multi-step data processing pipelines

Asynchronous Workflows

• Event-Driven: Triggered by domain events and messages
• Scheduled: Time-based execution (cron-like scheduling)
• Long-Running: Processes that span extended time periods

Human-in-the-Loop

• Approval Workflows: Require manual approval steps
• Review Processes: Content moderation and quality assurance
• Exception Handling: Manual intervention for error resolution

Error Handling Strategies

Retry Policies

const retryPolicy = {
  maximumAttempts: 3,
  initialInterval: '1s',
  backoffCoefficient: 2.0,
  maximumInterval: '30s',
  nonRetryableErrorTypes: ['ValidationError']
};

Compensation Actions

class BookingWorkflow {
  async execute(booking: Booking) {
    const reservation = await this.reserveRoom(booking);
    
    try {
      const payment = await this.processPayment(booking);
      const confirmation = await this.confirmBooking(booking, payment);
      return confirmation;
    } catch (error) {
      // Compensate - cancel the reservation
      await this.cancelReservation(reservation.id);
      throw error;
    }
  }
}

Circuit Breaker Integration

@workflow.defn()
export class ResilientWorkflow {
  async callExternalService(data: any) {
    return await workflow.executeActivity(
      externalServiceCall,
      data,
      {
        retry: { maximumAttempts: 3 },
        timeout: '30s'
      }
    );
  }
}

Monitoring and Observability

Workflow Metrics

• Execution Time: Track workflow duration and performance
• Success Rate: Monitor completion vs. failure rates
• Step Performance: Identify bottlenecks in workflow steps
• Resource Usage: Monitor CPU, memory, and I/O consumption

Distributed Tracing

import { trace } from '@opentelemetry/api';

@workflow.defn()
export class TracedWorkflow {
  async execute(input: any) {
    const span = trace.getActiveSpan();
    span?.setAttributes({
      'workflow.id': workflow.workflowId(),
      'workflow.type': 'order-processing'
    });
    
    // Workflow logic with automatic trace propagation
    return await this.processSteps(input);
  }
}

Best Practices

Design Principles

• Idempotency: Ensure workflow steps can be safely retried
• Atomicity: Design compensatable operations
• Visibility: Provide clear workflow progress indicators
• Testability: Enable unit and integration testing

Performance Optimization

• Parallel Execution: Run independent steps concurrently
• Batch Processing: Group similar operations when possible
• Resource Pooling: Reuse connections and expensive resources
• Caching: Cache intermediate results when appropriate

Security Considerations

• Input Validation: Validate all workflow inputs and parameters
• Access Control: Implement proper authorization checks
• Audit Logging: Log all workflow executions and decisions
• Data Protection: Encrypt sensitive data in workflow state

Integration Patterns

Event Sourcing

class WorkflowEventStore {
  async appendEvent(workflowId: string, event: WorkflowEvent) {
    await this.eventStore.append(`workflow-${workflowId}`, event);
  }
  
  async getWorkflowHistory(workflowId: string): Promise<WorkflowEvent[]> {
    return await this.eventStore.getEvents(`workflow-${workflowId}`);
  }
}

Message Queue Integration

@workflow.defn()
export class MessageDrivenWorkflow {
  async waitForApproval(requestId: string): Promise<ApprovalResult> {
    // Wait for approval message with timeout
    return await workflow.condition(
      () => this.approvalReceived,
      '24h' // 24 hour timeout
    );
  }
}

Testing Strategies

Unit Testing

describe('OrderWorkflow', () => {
  it('should complete order processing', async () => {
    const { client, nativeConnection } = await WorkflowTestEnvironment.createLocal();
    
    const result = await client.workflow.execute(OrderProcessingWorkflow, {
      workflowId: 'test-order-123',
      taskQueue: 'test-queue',
      args: [mockOrder]
    });
    
    expect(result.status).toBe('completed');
  });
});

Integration Testing

describe('Workflow Integration', () => {
  it('should handle service failures gracefully', async () => {
    // Mock external service failure
    mockService.processPayment.mockRejectedValue(new Error('Payment failed'));
    
    const result = await executeWorkflow(testOrder);
    
    expect(result.status).toBe('compensated');
    expect(mockService.cancelReservation).toHaveBeenCalled();
  });
});

Related Components

• Orchestrators: Higher-level workflow coordination
• Services: Individual workflow steps and activities
• Tasks: Atomic units of work within workflows
• Routers: Message routing for workflow communication