py-orchestrate 1.0.2

A Python workflow orchestrator with embedded SQLite database, similar to Durable Functions

py-orchestrate

A Python workflow orchestrator with durable recovery and pluggable persistence backends.

Features

• Workflow Orchestration: Define workflows that orchestrate multiple activities
• Persistent State: Persist workflow and activity state in SQLite or custom backends
• Fault Tolerance: Workflows can be resumed after application restart
• Activity Tracking: Track current activity execution and progress
• Background Execution: Workflows run asynchronously in background threads
• Simple API: Easy-to-use decorators for defining workflows and activities
• Extensible Storage: Built-in SQLite manager and optional Azure Cosmos DB manager

Installation

From PyPI (Recommended)

# Install using pip
pip install py-orchestrate

# Optional Cosmos DB support
pip install py-orchestrate[cosmos]

# Or using uv
uv add py-orchestrate

From Source

# Clone the repository
git clone https://github.com/your-username/py-orchestrate.git
cd py-orchestrate

# Install using uv
uv pip install -e .

# Or using pip
pip install -e .

Quick Start

1. Define Activities

Activities are individual units of work that can be orchestrated by workflows:

from py_orchestrate import activity

@activity("fetch_data")
def fetch_data(source: str) -> dict:
    # Your activity logic here
    return {"data": f"data_from_{source}", "count": 100}

@activity("process_data")  
def process_data(data: dict) -> dict:
    processed_count = data.get("count", 0) * 2
    return {"processed_data": data["data"] + "_processed", "processed_count": processed_count}

2. Define Workflows

Workflows orchestrate multiple activities:

from py_orchestrate import workflow

@workflow("data_processing_workflow")
def data_processing_workflow(source: str, destination: str) -> dict:
    # Step 1: Fetch data
    raw_data = fetch_data(source)
    
    # Step 2: Process data  
    processed_data = process_data(raw_data)
    
    # Step 3: Return result
    return {
        "workflow_completed": True,
        "total_processed": processed_data["processed_count"]
    }

3. Run the Orchestrator

from py_orchestrate import Orchestrator

# Create and start orchestrator
orchestrator = Orchestrator()
orchestrator.start()

try:
    # Invoke a workflow
    workflow_id = orchestrator.invoke_workflow(
        "data_processing_workflow",
        source="database", 
        destination="warehouse"
    )
    
    # Monitor progress
    status = orchestrator.get_workflow_status(workflow_id)
    print(f"Status: {status['status']}")
    print(f"Current activity: {status['current_activity']}")
    
finally:
    orchestrator.stop()

4. Use a Different Database Manager

from azure.identity import DefaultAzureCredential
from py_orchestrate import CosmosDatabaseManager, Orchestrator

db_manager = CosmosDatabaseManager(
    endpoint="https://<account>.documents.azure.com:443/",
    credential=DefaultAzureCredential(),
    database_id="py-orchestrate",
    workflow_container_id="workflows",
    activity_container_id="activity-executions",
)

orchestrator = Orchestrator(db_manager=db_manager)
orchestrator.start()

Core Concepts

Workflows

• State orchestrators that coordinate multiple activities
• Can have status: "processing", "done", or "failed"
• Run asynchronously in the background
• State is persisted and can resume after application restart

Activities

• Individual units of work executed by workflows
• Must use basic types (dict, list, str, int, etc.) for parameters and return values
• Cannot pass objects between activities
• Execution is tracked and persisted

Orchestrator Engine

• Manages workflow and activity execution
• Persists state through a database manager interface
• Provides APIs to invoke workflows and query status
• Handles fault tolerance and recovery

Database Managers

• SQLiteDatabaseManager: default file-based persistence
• CosmosDatabaseManager: Azure Cosmos DB backend with automatic database/container creation
• BaseDatabaseManager: interface for custom persistence implementations

Activity Signature Changes & Best Practices

⚠️ Important: Changing activity function signatures can cause workflow failures. This section explains the behavior and provides best practices.

How Recovery Works

py-orchestrate uses activity-level recovery with intelligent caching:

1. Workflow function restarts: The workflow function code begins executing from the top
2. Completed activities use cache: Activities that finished successfully return cached results instantly
3. Only incomplete work re-executes: Activities that were interrupted or failed run again
4. No completed work is lost: All successful activity results are preserved in the database

Example Recovery Flow:

@workflow("data_processing")
def data_processing(source: str) -> dict:
    data = fetch_data(source)          # ← If completed: returns cached result instantly
    processed = process_data(data)     # ← If interrupted here: re-executes normally  
    result = save_results(processed)   # ← Continues from interruption point
    return result

This provides efficient recovery - the workflow "replays" its execution path but skips completed work.

Signature Change Behavior

✅ Safe Changes (No Issues)

# ✅ Adding optional parameters (backward compatible)
@activity("process_data")
def process_data(data: str, mode: str = "default") -> dict:
    return {"processed": data, "mode": mode}

# ✅ Using different activity names (versioning)
@activity("process_data_v2")  
def process_data_v2(data: str, enhanced: bool = True) -> dict:
    return {"processed": data, "enhanced": enhanced}

❌ Unsafe Changes (Will Cause Errors)

# ❌ Removing parameters
@activity("process_data")
def process_data(data: str) -> dict:  # Removed 'mode' parameter
    return {"processed": data}

# ❌ Changing parameter types
@activity("process_data") 
def process_data(data: dict) -> dict:  # Changed str -> dict
    return {"processed": data}

# ❌ Adding required parameters
@activity("process_data")
def process_data(data: str, required_param: str) -> dict:  # No default value
    return {"processed": data, "required": required_param}

Error Examples

When signature mismatches occur, you'll see clear error messages:

# Error: "too many positional arguments"
# Caused by: Workflow calls activity(param1, param2) but activity only accepts activity(param1)

# Error: "missing required positional argument"  
# Caused by: Workflow calls activity(param1) but activity requires activity(param1, param2)

# Error: "argument of type 'dict' is not iterable"
# Caused by: Type mismatch between expected and actual parameter types

Best Practices

1. Version Your Activities

# Good: Use versioned activity names
@activity("fetch_data_v1")
def fetch_data_v1(source: str) -> dict:
    return {"data": f"v1_{source}"}

@activity("fetch_data_v2") 
def fetch_data_v2(source: str, timeout: int = 30) -> dict:
    return {"data": f"v2_{source}", "timeout": timeout}

# Update workflows to use new versions
@workflow("data_processing_v2")
def data_processing_v2(source: str) -> dict:
    data = fetch_data_v2(source, timeout=60)  # Use new version
    return {"result": data}

2. Only Add Optional Parameters

# Good: Backward compatible changes
@activity("process_item")
def process_item(item: dict, 
                validation: bool = True,    # Added optional
                timeout: int = 30) -> dict: # Added optional
    result = {"processed": item}
    if validation:
        result["validated"] = True
    return result

3. Use Defensive Programming

# Good: Handle different signatures gracefully
@activity("flexible_processor")
def flexible_processor(*args, **kwargs) -> dict:
    # Handle both old and new calling patterns
    if len(args) == 1:
        # Old signature: flexible_processor(data)
        data = args[0]
        options = {}
    elif len(args) == 2:
        # New signature: flexible_processor(data, options)
        data, options = args
    else:
        # Keyword arguments
        data = kwargs.get('data')
        options = kwargs.get('options', {})
    
    return {"processed": data, "options": options}

4. Test Signature Changes

# Always test workflows after activity changes
def test_signature_compatibility():
    orchestrator = Orchestrator("test.db")
    orchestrator.start()
    
    try:
        # Test new signature
        workflow_id = orchestrator.invoke_workflow("my_workflow", input="test")
        status = orchestrator.get_workflow_status(workflow_id)
        
        if status['status'] == 'failed':
            print(f"Signature error: {status['error_message']}")
            
    finally:
        orchestrator.stop()

Activity Implementation Changes During Recovery

Important: py-orchestrate uses activity-level caching during recovery, which has important implications for activity changes:

✅ Safe Scenarios (No Issues)

1. Activity logic changes after completion:

   # Original implementation (already completed and cached)
   @activity("process_data")
   def process_data(data: str) -> dict:
       return {"result": f"old_logic_{data}"}
   
   # New implementation (won't affect cached result)
   @activity("process_data")  
   def process_data(data: str) -> dict:
       return {"result": f"new_logic_{data}"}
   

   Result: Workflow uses cached result from original implementation

2. Missing activities after completion:

   # If activity was deleted but already completed
   # Result: Workflow uses cached result, doesn't try to re-execute
   

⚠️ Risky Scenarios (Will Cause Failures)

1. Missing activities for incomplete work:

   # If workflow was interrupted during this activity
   # and then activity is deleted/renamed
   # Result: "Activity 'process_data' not found" error
   

2. Signature changes for incomplete work:

   # If workflow was interrupted during this activity
   # and then signature changes incompatibly  
   # Result: Signature mismatch errors (as documented above)
   

🔧 Best Practices for Activity Changes

1. Wait for workflows to complete before making breaking changes
2. Use activity versioning for major changes:

   @activity("process_data_v1")  # Keep old version
   @activity("process_data_v2")  # Add new version
   

3. Check for running workflows before deployments:

   # Check for processing workflows
   processing_workflows = orchestrator.list_workflows()
   active = [wf for wf in processing_workflows if wf['status'] == 'processing']
   if active:
       print(f"Warning: {len(active)} workflows still processing")
   

Recovery from Signature Errors

If you encounter signature mismatch errors:

1. Check the error message - it tells you exactly what's wrong
2. Fix the activity signature - make it backward compatible
3. Or create a new versioned activity - safer approach
4. Test the fix - ensure existing workflows can complete

Migration Strategy

When you need to change activity signatures:

# Step 1: Create new versioned activity
@activity("process_data_v2")
def process_data_v2(data: str, new_param: str = "default") -> dict:
    return {"processed": data, "new_param": new_param}

# Step 2: Keep old activity for compatibility (optional)
@activity("process_data_v1") 
def process_data_v1(data: str) -> dict:
    # Delegate to new version with defaults
    return process_data_v2(data, "legacy_default")

# Step 3: Update new workflows to use v2
@workflow("new_workflow")
def new_workflow(input: str) -> dict:
    result = process_data_v2(input, "enhanced")  # Use new version
    return {"result": result}

# Step 4: Migrate existing workflows gradually

API Reference

Decorators

@workflow(name=None)

Marks a function as a workflow.

Parameters:

• name (str, optional): Name for the workflow. Defaults to function name.

@activity(name=None)

Marks a function as an activity.

Parameters:

• name (str, optional): Name for the activity. Defaults to function name.

Orchestrator Class

Orchestrator(db_path="py_orchestrate.db", max_workers=5, db_manager=None)

Creates a new orchestrator instance.

Parameters:

• db_path (str): Path to SQLite database file used when db_manager is not provided
• max_workers (int): Maximum number of concurrent workflow threads
• db_manager (BaseDatabaseManager, optional): Inject a custom database manager implementation

Methods

start()

Starts the orchestrator engine.

stop()

Stops the orchestrator engine and waits for workflows to complete.

invoke_workflow(name: str, **kwargs) -> str

Invokes a workflow by name with input parameters.

Returns: Workflow ID for tracking execution

get_workflow_status(workflow_id: str) -> dict

Gets the current status of a workflow.

Returns: Dictionary with workflow status information:

{
    "id": "workflow-id",
    "name": "workflow-name", 
    "status": "processing|done|failed",
    "current_activity": "activity-name or None",
    "error_message": "error message or None",
    "output": "workflow output or None",
    "created_at": "ISO timestamp",
    "updated_at": "ISO timestamp" 
}

list_workflows(name: str = None) -> List[dict]

Lists workflows, optionally filtered by name.

Database Schema

The built-in persistence layer stores two logical collections of data:

• workflows: Workflow instances and their current state
• activity_executions: Individual activity runs for each workflow

SQLite stores these as tables. Cosmos DB stores them in two containers, which should use separate container IDs for better partitioning:

• workflow_container_id
• activity_container_id

Examples

See main.py for a complete working example.

Troubleshooting

Common Issues

Workflow Stuck in "processing" Status

# Check current activity and error message
status = orchestrator.get_workflow_status(workflow_id)
print(f"Status: {status['status']}")
print(f"Current Activity: {status.get('current_activity')}")
print(f"Error: {status.get('error_message')}")

Possible causes:

• Activity is taking longer than expected
• Activity crashed without proper error handling
• Database connection issues

"too many positional arguments" Error

Cause: Activity signature was reduced (fewer parameters) Solution: Add back removed parameters or create new versioned activity

"missing required positional argument" Error

Cause: Activity signature was expanded (more required parameters) Solution: Make new parameters optional with default values

Workflows Not Resuming After Restart

Possible causes:

• Activity functions not registered (missing imports)
• Activity names changed
• Database file moved or deleted

Solution:

# Ensure all activities are imported and registered
from my_activities import fetch_data, process_data  # Import activities
from py_orchestrate import Orchestrator

orchestrator = Orchestrator()  
orchestrator.start()  # Recovery happens automatically

Database Corruption

Prevention:

• Don't modify the SQLite database manually
• Use proper shutdown: orchestrator.stop()
• Backup database files in production

Recovery:

# Check database integrity
import sqlite3
conn = sqlite3.connect("my_workflows.db")
conn.execute("PRAGMA integrity_check;")

Debugging Tips

Enable Detailed Logging

import logging
logging.basicConfig(level=logging.DEBUG)

# Now you'll see detailed orchestrator logs
orchestrator = Orchestrator()

Inspect Database State

# Check workflow status directly
workflows = orchestrator.list_workflows("my_workflow_name")
for wf in workflows:
    print(f"ID: {wf['id']}, Status: {wf['status']}")

Test Activities in Isolation

# Test activity functions directly before using in workflows
@activity("test_activity")
def test_activity(param: str) -> dict:
    return {"result": param}

# Test directly
result = test_activity("test_input")
print(result)  # Should work before putting in workflow

Requirements

• Python 3.12+
• SQLite (included with Python)
• azure-cosmos only when using CosmosDatabaseManager

Development

Setting up for Development

# Clone the repository
git clone https://github.com/your-username/py-orchestrate.git
cd py-orchestrate

# Install development dependencies
uv sync --dev

# Run the example
uv run python py_orchestrate/example.py

# Run automated tests
uv run pytest tests

# Run type checking
uv run mypy py_orchestrate --ignore-missing-imports

# Format code
uv run black py_orchestrate

# Build package
uv run python -m build

Release Process

This project uses GitHub Actions for automated building and publishing to PyPI.

License

MIT License