Workers Guide

Starting the worker

If you have defined a Faust app in the module

import faust

app = faust.App('proj', broker='kafka://localhost:9092')

async def process(stream):
    async for value in stream:

You can start the worker in the foreground by executing the command:

$ faust -A proj worker -l info

For a full list of available command-line options simply do:

$ faust worker --help

You can start multiple workers for the same app on the same machine, but be sure to provide a unique web server port to each worker, and also a unique data directory.

Start first worker:

$ faust --datadir=/var/faust/worker1 -A proj -l info worker --web-port=6066

Then start the second worker:

$ faust --datadir=/var/faust/worker2 -A proj -l info worker --web-port=6067

Stopping the worker

Shutdown should be accomplished using the TERM signal.

When shutdown is initiated the worker will finish all currently executing tasks before it actually terminates. If these tasks are important, you should wait for it to finish before doing anything drastic, like sending the KILL signal.

If the worker won’t shutdown after considerate time, for being stuck in an infinite-loop or similar, you can use the KILL signal to force terminate the worker. The tasks that did not complete will be executed again by another worker.

Starting subprocesses

For Faust applications that start subprocesses as a side effect of processing the stream, you should know that the “double-fork” problem on Unix means that the worker will not be able to reap its children when killed using the KILL signal.

To kill the worker and any child processes, this command usually does the trick:

$ pkill -9 -f 'faust'

If you don’t have the pkill command on your system, you can use the slightly longer version:

$ ps auxww | grep 'faust' | awk '{print $2}' | xargs kill -9

Restarting the worker

To restart the worker you should send the TERM signal and start a new instance.

Process Signals

The worker’s main process overrides the following signals:


Warm shutdown, wait for tasks to complete.


Cold shutdown, terminate ASAP


Dump traceback for all active threads.