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Resiliency & Compensation

This tutorial demonstrates how to improve resiliency when activities are executed and how to include compensation actions when activities return an error. For more on workflow resiliency read the Dapr docs.

Inspect the code

Open the resiliency_and_compensation_workflow.py file in the tutorials/workflow/python/resiliency-and-compensation/resiliency_and_compensation folder. This file contains the definition for the workflow. This workflow implements an activity retry policy on all the associated activities and compensating logic if an activity throws an exception.

graph LR
   SW((Start
   Workflow))
   A1[minus_one]
   A2[division]
   EX{Division
   Exception?}
   A3[plus_one]
   EW((End
   Workflow))
   SW --> A1
   A1 --> A2
   A2 --> EX
   EX -- yes --> A3
   EX -- no --> EW
   A3 --> EW

Run the tutorial

Use a terminal to navigate to the tutorials/workflow/python/resiliency-and-compensation/resiliency_and_compensation folder.
Install the dependencies using pip:
```
pip3 install -r requirements.txt
```
Navigate one folder back to resiliency-and-compensation and use the Dapr CLI to run the Dapr Multi-App run file
```
```bash
```
dapr run -f .
```

```
Use the POST request in the resiliency-compensation.http file to start the workflow with a workflow input value of 1, or use this cURL command:
```
curl -i --request POST \
--url http://localhost:5264/start/1
```
When the workflow input is 1, the minus_one activity will subtract 1 resulting in a 0. This value is passed to the division activity, which will throw an error because the divisor is 0. The division activity will be retried three times but all will fail the same way as the divisor has not changed. Finally the compensation action plus_one will be executed, increasing the value back to 1 before returning the result.

The app logs should output the following:
```
== APP - resiliency == minus_one: Received input: 1.
== APP - resiliency == division: Received divisor: 0.
== APP - resiliency == division: Received divisor: 0.
== APP - resiliency == division: Received divisor: 0.
== APP - resiliency == plus_one: Received input: 0.
```
Use the GET request in the resiliency-compensation.http file to get the status of the workflow, or use this cURL command:
```
curl --request GET --url http://localhost:3564/v1.0/workflows/dapr/<INSTANCEID>
```
Where <INSTANCEID> is the workflow instance ID you received in the instance_id property in the previous step.

Since 1 is used as the input, the expected serialized output of the workflow is:
```
"1"
```
The expected serialized custom status field of the workflow output is:
```
"\"Compensated minus_one activity with plus_one activity.\""
```
Stop the Dapr Multi-App run process by pressing Ctrl+C.

3.4 KiB Raw Blame History

Resiliency & Compensation

Inspect the code

Run the tutorial

3.4 KiB

Raw Blame History