pvsone / temporal-sagas

Sagas

Sagas are a protocol for implementing long-running processes. The Saga protocol ensures that a process is atomic, that is, a process executes observably equivalent to completely or not at all.

Overview

The booking saga workflow is responsible for coordinating the booking of a vacation package, consisting of a car, hotel, and flight reservation. In the event of a failure at any point during the booking process, the workflow will trigger compensating actions to undo any previous bookings.

Running

Prerequisites:

• Python >= 3.7
• Poetry
• Local Temporal server running

With this repository cloned, run the following at the root of the directory:

poetry install --no-root

That loads all required dependencies.

Then run the worker and workflow.

poetry run python run_worker.py
poetry run python run_workflow.py

Demo: Happy Path

Enter your booking information in the Flask app http://127.0.0.1:5000, then see the tasks in the Web UI at http://localhost:8233/.

Select your running or completed Workflow ID.

Under WorkflowExecutionCompleted car, hotel and flight are booked.

Notice each is executed via an activity.

Demo: Recover Forward (retries)

Modify Attempts = 1 to Attempts = 3 in UI, so that the booking activities attempt a retry 3 times. Render your booking information in the Flask app http://127.0.0.1:5000, then see the tasks in the Web UI at http://localhost:8233/.

Select your running or completed Workflow ID.

Under Recent events, select the failed Activity, book_flight (in compact view).

Under ActivityTaskStarted you'll see the Attempts (3), and the stack trace message letting you know the last failed attempt.

Then notice how the Workflow executes the compensations.

Demo: Recover Backward (rollback)

Modify Flight = Alaska Airlines 123 to Flight = invalid in the UI, so that the book_flight Activity fails and a rollback occurs. Render your booking information in the Flask app http://127.0.0.1:5000, then see the tasks in the Web UI at http://localhost:8233/.

Select your running or completed Workflow ID.

Under Recent events, select the failed Activity, book_flight (in compact view).

Under ActivityTaskStarted you'll see the Attempts (5), and the stack trace message letting you know the last failed attempt.

Under ActivityTaskFailed you'll see error Invalid flight booking, rolling back!. You will also see that since the booking cannot be completed, rollback (undo) is performed using compensation.

Design

The booking saga is implemented using the Temporal Workflow framework, which provides a robust and fault-tolerant platform for coordinating distributed transactions.

The saga workflow consists of three activities: book_car(), book_hotel)(), and book_flight)(), each of which is responsible for making a reservation with the corresponding service provider. If any of these activities fail, the workflow will trigger the corresponding compensating action (undo_book_car(), undo_book_hotel(), or undo_book_flight()) to undo any previous bookings.

The non_retryable_error_types parameter is used to specify a list of error types that should not be retried when a Workflow or Activity fails.