zeebe-rest-api

How do I wrap a workflow with a single REST request-response in Zeebe? That is to say: create an instance on the request, and send some final output of the workflow in the response. Here are two different ways to do that.

Prerequisites

Node.js
Zeebe - Docker compose config here

To Install

npm i -g ts-node
npm i

1. Synchronous Response

Uses an event emitter to pass a result from a workflow execution to a HTTP response.

To Run:

Start the Zeebe broker.
Start the REST Server (starts workers and deploys workflow): ts-node src/synchronous-response/index.ts.
Open 127.0.0.1:3000 (or curl it).

You'll see output like this:

zeebe-rest-api on  master [?] is 📦 v1.0.0 via ⬢ v10.9.0
➜ curl 127.0.0.1:3000
{"number":0.7504228909151884}%

This relies on workers running in a single Node process for affinity. To extend this to a scalable pool of workers, you would need to use a distributed pub/sub broker like Redis or Hazelcast.

2. Callback Route

Cache the outcome of a workflow, and send the client a results URL that it can poll.

To Run:

Start the Zeebe broker.
Start the REST Server (starts workers and deploys workflow): ts-node src/synchronous-response/index.ts.
Open 127.0.0.1:3000 (or curl it).

You'll see output like this:

zeebe-rest-api on  master [!?] is 📦 v1.0.0 via ⬢ v10.9.0
➜ curl 127.0.0.1:3000
{"resultsUrl":"http://127.0.0.1:300/results/9685"}%

Now, curl the resultsUrl to collect the result:

zeebe-rest-api on  master [!?] is 📦 v1.0.0 via ⬢ v10.9.0
➜ curl http://127.0.0.1:3000/results/9685
{"status":"Done","result":0.8547789402934958}%

Scaling the workers

Note that this will only work when you have a single worker, running in the same process as the REST server. With more than one worker, you cannot guarantee affinity. To do that, you need to implement distributed pub/sub using Redis or similar. You can see a proof-of-concept that uses a singleton affinity process on the network and websockets, here: https://github.com/jwulf/zeebe-affinity-service