quickstarts/workflows/python/sdk

Dapr workflows

In this quickstart, you'll create a simple console application to demonstrate Dapr's workflow programming model and the workflow management API. The console app starts and manages an order processing workflow.

This quickstart includes one project:

• Python console app order-processor

The quickstart contains 1 workflow (order_processing_workflow) which simulates purchasing items from a store, and 5 unique activities within the workflow. These 5 activities are as follows:

• notify_activity: This activity utilizes a logger to print out messages throughout the workflow. These messages notify the user when there is insufficient inventory, their payment couldn't be processed, and more.
• process_payment_activity: This activity is responsible for processing and authorizing the payment.
• verify_inventory_activity: This activity checks the state store to ensure that there is enough inventory present for purchase.
• update_inventory_activity: This activity removes the requested items from the state store and updates the store with the new remaining inventory value.
• requst_approval_activity: This activity seeks approval from Manager, if payment is greater than 50000 USD.

Run the order processor workflow

1. Open a new terminal window and navigate to order-processor directory:

cd ./order-processor
pip3 install -r requirements.txt
cd ..

2. Run the console app with Dapr:

dapr run -f .

3. Expected output

==========Begin the purchase of item:==========
Starting order workflow, purchasing 10 of cars
INFO:NotifyActivity:Received order b903d749cd814e099f06ebf4a56a2f90 for 10 cars at $150000 !
INFO:VerifyInventoryActivity:Verifying inventory for order b903d749cd814e099f06ebf4a56a2f90 of 10 cars
INFO:VerifyInventoryActivity:There are 100 Cars available for purchase
INFO:RequestApprovalActivity:Requesting approval for payment of 150000 USD for 10 cars
INFO:NotifyActivity:Payment for order b903d749cd814e099f06ebf4a56a2f90 has been approved!
INFO:ProcessPaymentActivity:Processing payment: b903d749cd814e099f06ebf4a56a2f90 for 10 cars at 150000 USD
INFO:ProcessPaymentActivity:Payment for request ID b903d749cd814e099f06ebf4a56a2f90 processed successfully
INFO:UpdateInventoryActivity:Checking inventory for order b903d749cd814e099f06ebf4a56a2f90 for 10 cars
INFO:UpdateInventoryActivity:There are now 90 cars left in stock
INFO:NotifyActivity:Order b903d749cd814e099f06ebf4a56a2f90 has completed!
Workflow completed! Result: Completed
  Purchase of item is  Completed

4. Stop Dapr workflow with CTRL-C or:

dapr stop -f .

View workflow output with Zipkin

For a more detailed view of the workflow activities (duration, progress etc.), try using Zipkin.

1. View Traces in Zipkin UI - In your browser go to http://localhost:9411 to view the workflow trace spans in the Zipkin web UI. The order-processor workflow should be viewable with the following output in the Zipkin web UI. Note: the openzipkin/zipkin docker container is launched on running dapr init.

What happened?

When you ran dapr run --app-id order-processor --resources-path ../../../components/ -- python3 app.py

1. First the user inputs an order for 10 cars into the concole app.
2. A unique order ID for the workflow is generated (in the above example, b903d749cd814e099f06ebf4a56a2f90) and the workflow is scheduled.
3. The NotifyActivity workflow activity sends a notification saying an order for 10 cars has been received.
4. The VerifyInventoryActivity workflow activity checks the inventory data, determines if you can supply the ordered item, and responds with the number of cars in stock.
5. The RequestApprovalActivity workflow activity is triggered due to buisness logic for orders exceeding $50k and user is prompted to manually approve the purchase before continuing order.
6. The workflow starts and notifies you of its status.
7. The ProcessPaymentActivity workflow activity begins processing payment for order b903d749cd814e099f06ebf4a56a2f90 and confirms if successful.
8. The UpdateInventoryActivity workflow activity updates the inventory with the current available cars after the order has been processed.
9. The NotifyActivity workflow activity sends a notification saying that order b903d749cd814e099f06ebf4a56a2f90 has completed.
10. The workflow terminates as completed.