rophy / nats-temporal-bridge

nats-temporal-bridge

A web service that connect Temporal signals with NATS events.

Temporal workflows are implemented as activities, the activities cannot be long-running services, as these activities are supposed to be steps of a distributed workflow.

While you can implement a repeating activity that polls for NATS events continuously, it's much more effective to have a long-running service that subscribe to NATS events.

This web service acts as the bridge between NATS events and Temporal workflows. It is a long-running web service that subscribes to NATS topics, and signals Temporal workflows as necssary.

Getting Started

Assuming both NATS and Temporal service are running on localhost with default ports.

First, start this bridge service:

npm install
node app.js

Then, you can create a temporal workflow like this:

import { proxyActivities } from '@temporalio/workflow';
import * as wf from '@temporalio/workflow';

// Only import the activity types
import type * as activities from './activities';

const { waitNatsEvent } = proxyActivities<typeof activities>({});

export const unblockSignal = wf.defineSignal<[string]>('unblock');
export const isBlockedQuery = wf.defineQuery<boolean>('isBlocked');

/** A workflow that simply calls an activity */
export async function example(name: string): Promise<string> {
  let isBlocked = true;
  let result = "";
  wf.setHandler(unblockSignal, (payload: string) => {
    isBlocked = false;
    result = payload;
  });
  wf.setHandler(isBlockedQuery, () => isBlocked);

  await waitNatsEvent(name, 'unblock');

  console.log('Blocked');
  try {
    await wf.condition(() => !isBlocked);
    console.log('Unblocked', result);
  } catch (err) {
    if (err instanceof wf.CancelledFailure) {
      console.log('Cancelled');
    }
    throw err;
  }
  return result;
}

With the waitNatsEvent activity as:

import { Context } from '@temporalio/activity'
import axios from 'axios';

export async function waitNatsEvent(subject: string, signal: string): Promise<string> {
  let info = Context.current().info;
  let resp = await axios.post('http://localhost:3000/subscribe', {
    subject: subject,
    namespace: info.activityNamespace,
    workflowId: info.workflowExecution.workflowId,
    signal: signal
  });
  return `response=${resp.status}`;
}