DBOS Python Best Practices

Guide for building reliable, fault-tolerant Python applications with DBOS durable workflows.

When to Apply

Reference these guidelines when:

Adding DBOS to existing Python code
Creating workflows and steps
Using queues for concurrency control
Implementing workflow communication (events, messages, streams)
Configuring and launching DBOS applications
Using DBOSClient from external applications
Testing DBOS applications

Rule Categories by Priority

Priority	Category	Impact	Prefix
1	Lifecycle	CRITICAL	`lifecycle-`
2	Workflow	CRITICAL	`workflow-`
3	Step	HIGH	`step-`
4	Queue	HIGH	`queue-`
5	Communication	MEDIUM	`comm-`
6	Pattern	MEDIUM	`pattern-`
7	Testing	LOW-MEDIUM	`test-`
8	Client	MEDIUM	`client-`
9	Advanced	LOW	`advanced-`

Critical Rules

DBOS Configuration and Launch

A DBOS application MUST configure and launch DBOS inside its main function:

import os
from dbos import DBOS, DBOSConfig

@DBOS.workflow()
def my_workflow():
    pass

if __name__ == "__main__":
    config: DBOSConfig = {
        "name": "my-app",
        "system_database_url": os.environ.get("DBOS_SYSTEM_DATABASE_URL"),
    }
    DBOS(config=config)
    DBOS.launch()

Workflow and Step Structure

Workflows are comprised of steps. Any function performing complex operations or accessing external services must be a step:

@DBOS.step()
def call_external_api():
    return requests.get("https://api.example.com").json()

@DBOS.workflow()
def my_workflow():
    result = call_external_api()
    return result

Key Constraints

Do NOT call DBOS.start_workflow or DBOS.recv from a step
Do NOT use threads to start workflows - use DBOS.start_workflow or queues
Workflows MUST be deterministic - non-deterministic operations go in steps
Do NOT create/update global variables from workflows or steps

How to Use

Read individual rule files for detailed explanations and examples:

references/lifecycle-config.md
references/workflow-determinism.md
references/queue-concurrency.md

dbos-python