NodeJS EventHub Triggers for local development

This project implements a bare-bones emulation of EventHubs for local development.

npm install --save-dev @openlearning/local-node-eventhub-trigger

yarn add --dev @openlearning/local-node-eventhub-trigger

This provides three scripts:

1. npx eventhub-local-init Initialising the project. This will create an eventhub-dev.json config file and an HTTP triggered utility function for triggering EventHub bindings (added to .funcignore as it is for local development only).
2. npx eventhub-local-dev Running a Redis Streams backed event queue with an AMQP interface. This interface emulates enough of the EventHubs protocol to use the NodeJS eventhubs library to query partition information and send events. The function runtime will not connect to this emulator so functions triggered by EventHub bindings will instead be triggered by an HTTP utility function (which exists only for local development).
3. npx eventhub-local-replay Replaying a Redis Stream into EventHub triggered functions (this removes all consumer groups and re-adds them, starting from the beginning of the stream).

Notes:

• This requires that your EventHub triggered functions are not provided a connection string (Azure Functions will not connect to this emulator). This will cause an error (of the effect: connection string cannot be null) and deactivate these functions. These functions will instead be triggered by the HTTP trigger utility.
• You may need to separate the connection string used for ingesting events (which will be this emulator on localhost) from the connection string used for triggering functions (not provided). These will be the same in production.

Requirements:

• NodeJS/Typescript Azure Functions runtime/core tools (v2.0)
• Redis >v5 (Redis Streams) is running

Example:

Start an Azure Functions Project:

1. Init the project with func init
2. Create a function which will receive and ingest EventHub events: func new and select "Azure Event Hub trigger", e.g. called "EventConsumer"

Send Events to an EventHub

1. Create a function (or other service) which will send events to EventHub: e.g. func new and select "HTTP trigger", called "EventApi"
2. Install the azure eventhub library to send events to EventHub from your API: npm install @azure/event-hubs
3. In "EventApi" (or other service) call the EventHubs library:

import { EventHubClient } from '@azure/event-hubs';

const localConnectionString = 'Endpoint=sb://localhost;SharedAccessKeyName=name;SharedAccessKey=key';
const eventHubClient = EventHubClient.createFromConnectionString(localConnectionString, 'myEventHub');
const partitionId = "0";

...

await eventHubClient.send(
  {
    body: event,
  },
  partitionId
);

This will send an event to the local eventhubs emulation, which will trigger the required "Azure Event Hub Trigger" functions (e.g. "EventConsumer").

General Azure Function Setup Notes

• tsconfig.json will likely require "esModuleInterop": true
• local.settings.json should be set up with "Values":
  • "AzureWebJobsStorage": "UserDevelopmentStorage=true" (which can use local Azure Storage emulation using azurite)
• Other local development NodeJS environment variables required:
  • "NODE_TLS_REJECT_UNAUTHORIZED": "0" (for sending to local self-signed TLS connections)