fn-zeebe

Fn Server with a built-in Zeebe.io extension

This is a prototype for a POC - it is not production ready!

Features of the Zeebe extension:

• Connects Fn functions to Zeebe to handle jobs. Each Fn function can be configured to handle a specific Zeebe job type.
• Starts Zeebe job workers which subscribe to the configured Zeebe job types and invoke the configured Fn functions
• Listens to the function deployment events to starts and stop the Zeebe job workers dynamically
• Provides a minimal REST endpoint to show the overview of registered Zeebe job workers

Requirements

• Zeebe (tested using version 0.20.0)
• Fn CLI (testet using version 0.5.65)
• Docker (tested using Engine version 18.09 and 19.03)

How to install the extension?

The Zeebe extension is built in to this fork of the Fn Repository. Build a new custom docker image of the Fn Server including the Zeebe extension:

docker build -t artunsubasi/fnserver .

The intended way of installing Fn extensions is building an Fn Server using the Fn CLI and an ext.yaml file referencing the public repository of the Fn extension. There is a public repository of the Zeebe extension here. However, this method currently does not work at this time because of Go dependency conflicts.

Starting the Fn server with the extension

Start the server using docker.

docker run --rm -i --name fnserver \
    -e FN_LB_URL=http://localhost:8080 \
    -e FN_API_SERVER_URL=http://localhost:8080 \
    -e FN_ZEEBE_GATEWAY_URL=http://localhost:26500 \
    -v ./fn/data:/app/data  \
    -v /var/run/docker.sock:/var/run/docker.sock  \
    -p 8080:8080  \
    imageuser/imagename

Environment variables

• FN_LB_URL: URL of the Fn Load Balancer. If using the all-in-one-mode, just point to the Fn server.
• FN_API_SERVER_URL: URL of the Fn API Server. If using the all-in-one-mode, just point to the Fn server.
• FN_ZEEBE_GATEWAY_URL: URL of the Zeebe Gateway (gRPC-Port)

Docker-Volumes

• /app/data ist the database storing the deployed apps, functions, etc.
• /var/run/docker.sock points to the Unix-Socket of the Docker-Daemon so that the Fn server can manage internal docker containers. This is needed because the Fn functions are startet within their own docker containers.

Configuring Fn functions to handle Zeebe jobs

Functions are configured to handle Zeebe jobs using the configuration parameter zeebe_job_type within the function configuration file func.yaml. An example of a function configuration:

schema_version: 20180708
name: collectmoney
version: 0.0.4
runtime: go
entrypoint: ./func
format: http-stream
config:
  zeebe_job_type: payment-service
triggers:
- name: payment-service-trigger
  type: http
  source: /payment-service

In the above example, the function collectmoney is configured to handle Zeebe jobs with the type payment-service. As soon as the function is deployed to the Fn, the extension launches Zeebe job workers and starts listening for available Zeebe jobs of the payment-service.

Restrictions

Fn functions which are configured to handle Zeebe jobs must return a Json object as a response. The POC does not provide an automatic output mapping. Therefore, other return types, including Json arrays as a root, lead to an incident in the corresponding Zeebe workflow instance.

fn-zeebe depends on the HTTP trigger of the Fn functions. Therefore, a worker is started only if a HTTP trigger is configured for the function.

Fn Server modes

Fn server can be built in different modes: all-in-one, load balancer, API server and Fn runner. The following documentation describes the usage for the all-in-one mode.