An External Worker Task in BPMN or CMMN is a task where the custom logic of that task is executed externally to Flowable, i.e. on another server. When the process or case engine arrives at such a task, it will create an external job, which is exposed over the REST API. Through this REST API, the job can be acquired and locked. Once locked, the custom logic is responsible for signalling over REST that the work is done and the process or case can continue.
This project makes implementing such custom logic in Python easy by not having the worry about the low-level details of the REST API and focus on the actual custom business logic. Integrations for other languages are available, too.
The different ways to authenticate are explained in the documentation of the underlying requests HTTP library which is used to connect to Flowable.
The ExternalWorkerClient accepts as a parameter auth an implementation of requests.auth.AuthBase.
There are default implementations for example for basic authentication e.g. HTTPBasicAuth("admin", "test").
Flowable offers a bearer token implementation FlowableCloudToken which allows to specify an access token to the Flowable Cloud offering.
To install the external worker library, execute the following command:
pip install flowable.external-worker-client
The usage with Flowable Cloud is simpler, since everything is pre-configured. However, it's required to either use the user credentials or to pre-configure a personal access token.
from flowable.external_worker_client import ExternalWorkerClient
from flowable.external_worker_client.cloud_token import FlowableCloudToken
client = ExternalWorkerClient(auth=FlowableCloudToken("<personal-access-token>"))
def my_callback(job, worker_result_builder):
print('Executed job: ' + job.id)
return worker_result_builder.success()
subscription = client.subscribe('myTopic', my_callback)The following is an example how you can connect to a Flowable instance running at http://localhost:8090 and process all messages retrieved on the topic myTopic:
from flowable.external_worker_client import ExternalWorkerClient
from requests.auth import HTTPBasicAuth
client = ExternalWorkerClient('http://localhost:8090/flowable-work', auth=HTTPBasicAuth("admin", "test"))
def my_callback(job, worker_result_builder):
print('Executed job: ' + job.id)
return worker_result_builder.success()
subscription = client.subscribe('myTopic', my_callback)