ProcessCube ETW Library

Build External Task Workers (ETW) for ProcessCube, featuring health checks, typed handlers, and environment-based configuration.

Installation

uv add processcube-etw-library

Configuration

Environment Variables

The library uses environment variables for configuration. You can set these in your environment or in a .env file in your project root.

Example .env File

PROCESSCUBE_ENGINE_URL=http://localhost:56000
PROCESSCUBE_ETW_CLIENT_ID=my_etw_client
PROCESSCUBE_ETW_CLIENT_SECRET=my_secret_key
PROCESSCUBE_ETW_CLIENT_SCOPES=engine_etw
ENVIRONMENT=production

Extending Settings

You can extend the base settings class to add your own environment variables:

from pydantic import Field
from processcube_etw_library.settings import ETWSettings, load_settings

class MyAppSettings(ETWSettings):
    database_url: str = Field(default="sqlite:///app.db")
    api_key: str = Field(default="")

# Load settings with your custom class
settings = load_settings(MyAppSettings)

Usage

Start the ETW Application

from processcube_etw_library import new_external_task_worker_app

# Create the application
app = new_external_task_worker_app()

# Run the application
app.run()

Subscribe to External Task Topics

from processcube_etw_library import new_external_task_worker_app

app = new_external_task_worker_app()

def my_handler(task):
    # Process the task
    result = {"processed": True}
    return result

# Subscribe to a topic
app.subscribe_to_external_task_for_topic("my-topic", my_handler)

app.run()

Typed Handlers

Use typed handlers for automatic payload validation with Pydantic models:

from pydantic import BaseModel
from processcube_etw_library import new_external_task_worker_app

class MyInput(BaseModel):
    name: str
    value: int

class MyOutput(BaseModel):
    result: str

app = new_external_task_worker_app()

def my_typed_handler(payload: MyInput) -> MyOutput:
    return MyOutput(result=f"Processed {payload.name} with value {payload.value}")

app.subscribe_to_external_task_for_topic_typed("my-typed-topic", my_typed_handler)

app.run()

Add a Custom Health Check

from processcube_etw_library import new_external_task_worker_app
from processcube_etw_library.health import HealthCheck, create_url_health_check

app = new_external_task_worker_app()

# Add a URL-based health check
app.add_health_check(
    HealthCheck(
        create_url_health_check("http://my-service:8080/health"),
        service_name="My Service",
        tags=["backend", "api"],
        comments=["Checks if My Service is reachable"],
    )
)

# Add a custom health check function
def check_database():
    # Return True if healthy, False otherwise
    try:
        # Your database check logic here
        return True
    except Exception:
        return False

app.add_health_check(
    HealthCheck(
        check_database,
        service_name="Database",
        tags=["backend", "database"],
        comments=["Checks database connectivity"],
    )
)

app.run()

Managing Health Checks

# Get all registered health checks
checks = app.get_health_checks()

# Get a specific health check by service name
db_check = app.get_health_check("Database")

# Remove a health check
app.remove_health_check("Database")

Disabling Built-in Health Checks

By default, the library registers health checks for the ProcessCube Engine and Authority. You can disable these:

app = new_external_task_worker_app(built_in_health_checks=False)

Health Endpoints

The application exposes health endpoints at /healthyz and /readyz that return the status of all registered health checks. To check if the application is running without performing health checks, use /livez.

Server Configuration

The server configuration is determined by the ENVIRONMENT variable: