Workers

A worker connects to the Cadence server, polls a task list for workflow and activity tasks, and executes them. Three objects work together: Client, Registry, and Worker.

Client

Client connects to the Cadence frontend over gRPC. It is an async context manager.

from cadence.client import Client

CADENCE_TARGET = "localhost:7833"  # replace with your Cadence frontend address

async with Client(domain="my-domain", target=CADENCE_TARGET) as client:
    # client is ready here
    ...

Option	Description
domain	Cadence domain (required)
target	Cadence frontend address, host:port (default: localhost:7833)
identity	Identity string shown in workflow history (default: auto-generated)
data_converter	Custom data converter for serializing workflow arguments

Registry

Registry holds workflow and activity definitions. Create one per worker process (or share one across multiple workers).

from cadence.worker import Registry

registry = Registry()

Register workflows and activities on the registry using decorators:

@registry.workflow()
class MyWorkflow:
    @workflow.run
    async def run(self, name: str) -> str:
        ...

@registry.activity()
async def my_activity(input: str) -> str:
    ...

You can also register definitions imperatively:

registry.register_activity(my_activity)

Worker

Worker is an async context manager that polls the task list and dispatches tasks.

from cadence.worker import Worker

async with Client(domain="my-domain", target=CADENCE_TARGET) as client:
    async with Worker(client, "my-task-list", registry):
        # Worker is polling; keep alive until interrupted
        await asyncio.Event().wait()

Worker runs two pollers internally: one for decision (workflow) tasks and one for activity tasks. Both run concurrently.

Disabling one poller

Worker(client, "my-task-list", registry, disable_activity_worker=True)
Worker(client, "my-task-list", registry, disable_workflow_worker=True)

Full example

import asyncio
from cadence.client import Client
from cadence.worker import Worker, Registry
from cadence import workflow

CADENCE_TARGET = "localhost:7833"  # replace with your Cadence frontend address

registry = Registry()

@registry.workflow()
class GreetingWorkflow:
    @workflow.run
    async def run(self, name: str) -> str:
        return f"Hello, {name}!"

async def main():
    async with Client(domain="my-domain", target=CADENCE_TARGET) as client:
        print("Worker running, press Ctrl-C to stop")
        async with Worker(client, "my-task-list", registry):
            await asyncio.Event().wait()

if __name__ == "__main__":
    try:
        asyncio.run(main())
    except KeyboardInterrupt:
        pass