Workleap Azure Event Grid Emulator

This is an open source emulator for Azure Event Grid that supports both the push delivery and the pull delivery models. Based on ASP.NET Core, this emulator provides a cross-platform experience for developers wanting to try Azure Event Grid easily in a local environment without having to deploy to Azure.

The emulator supports two Events delivery formats: Push and Pull.

This project is not affiliated, associated, authorized, endorsed by, or in any way officially connected with Microsoft.

Features

• Support publishing events to Custom Topics (EventGridEvents/CloudEvents) and Namespace Topics (only CloudEvents)
• Support Push & Pull Delivery Models
• Push delivery to configured webhooks defined in the emulator configuration file (more details below).
• Pull delivery API client commands supported in the emulator (more details below).
• Simple but durable message delivery and retry based on the Azure Event Grid documentation.
• Ability to add and remove topics and webhooks at runtime without having to restart the emulator.
• As the emulator is built on top of ASP.NET Core, you can follow this Microsoft documentation to run on HTTPS.

Prerequisites

You must have Docker installed. This Event Grid emulator is only distributed as a Docker image.

Getting started

The first step is to create a configuration file for the emulator to know the topics, and for each topic, the webhooks to call when an event is published. Create a configuration file named appsettings.json somewhere on your computer, for instance: C:\eventgridemulator\appsettings.json.

Push Delivery configuration

{
  "Topics": {
    "topic1": [
      "https://host.docker.internal:5122/my-webhook",
      "http://host.docker.internal:7221/eventgrid"
    ],
    "topic2": [
      "https://mydockercontainer:5122/eventgrid/domainevents"
    ],
  }
}

In the example for push delivery, we have two topics, topic1 and topic2. If an event is sent to the emulator on this URL http://127.0.0.1:6500/topic1/api/events, the emulator would forward the events to https://host.docker.internal:5122/my-webhook and http://host.docker.internal:7221/eventgrid on your host machine. As the emulator runs on Docker, you must use the host.docker.internal (emulator must make an http ) host whenever you want to call a webhook on your host machine.

Pull delivery configuration

{
  "Topics": {
    "topicfoobar": [
      "pull://foo-subscription",
      "pull://bar-subscription"
    ]
  }
}

In the example for pull delivery, we have a topics, topicfoobar. If an event is sent to the emulator on this URL http://127.0.0.1:6500/topics/topicfoobar:publish, the emulator would make the events available to pull at pull://foo-subscription and pull://bar-subscription on your host machine.

Run the Event Grid emulator with docker run

docker run -p 6500:6500 -v "C:/eventgridemulator/appsettings.json:/app/appsettings.json" --add-host=host.docker.internal:host-gateway workleap/eventgridemulator

--add-host=host.docker.internal:host-gateway is required for the emulator to be able to reach the webhooks on the host machine.

Run the Event Grid emulator with Docker Compose

Create a file named docker-compose.yaml and add this content:

version: '3'

services:
  eventgridemulator:
    image: workleap/eventgridemulator:latest
    ports:
      - "6500:6500"
    volumes:
      - "C:/eventgridemulator/appsettings.json:/app/appsettings.json"
    extra_hosts:
      - "host.docker.internal:host-gateway"

From the directory in which the file resides, run the docker compose up command.

Publish and Receive Events using Push Delivery for Custom Topic

Push Delivery: Now that the emulator is running, you can send both EventGridEvents and CloudEvents to the endpoint and receive them in your webhooks. If you're using C#, follow these steps from the Microsoft documentation:

// Change "my-topic" to the name of your topic.
// The authentication mechanism is actually ignored by the emulator.
// If you must provide a TokenCredential instead of an access key, the emulator must be running on HTTPS.
var client = new EventGridPublisherClient(
    new Uri("http://127.0.0.1:6500/my-topic/api/events"),
    new AzureKeyCredential("fakeAccessKey"));

// Create and send a CloudEvent to EventGrid
var cloudEvent = new new CloudEvent("<source>", "<type>", data);
await client.SendEventAsync(cloudEvent);

// Create and send an EventGridEvent to EventGrid
var eventGridEvent = new EventGridEvent(
    subject: "<source>",
    eventType: "<type>",
    dataVersion: "<version>",
    data: data);
await client.SendEventAsync(eventGridEvent);

// An url with the correct url would need to be exposed to process the push delivery events
[HttpPost("<my-topic endpoint defined in config>")]
public IActionResult Post([FromBody]EventGridEvent[] value)
{
...
}

Publish and Receive Events using Pull Delivery Model for Namespace Topic

Pull Delivery: Once the emulator is running, we can send CloudEvents to the endpoint and pull/acknowledge events with api calls.

We support the following Queue delivery APIs:

• PublishCloudEventsAsync: publishes an event from the queue.
• ReceiveCloudEventsAsync: receives an event from the queue.
• AcknowledgeCloudEventsAsync: acknowledges that the received event is processed successfully and delete from the queue.
• ReleaseCloudEventsAsync: releases the received event and requeues the event.
• RejectCloudEventsAsync: rejects the received event and delete from the queue.

// The authentication mechanism is actually ignored by the emulator.
// If you must provide a TokenCredential instead of an access key, the emulator must be running on HTTPS.
var client = new EventGridClient(
    new Uri("http://127.0.0.1:6500"),
    new AzureKeyCredential("fakeAccessKey"));

// Example of how to can publish an event with EventGridClient
client.PublishCloudEventsAsync(topicName, new CloudEvent("<source>", "<type>", data));

// Example of how to receive an event with EventGridClient
var events = await client.ReceiveCloudEventsAsync(topicName, eventSubscriptionName);

//  Example of how to can acknowledge an event from queue
// Reject/Release would be the same format except with RejectCloudEventsAsync/RejectOptions and ReleaseCloudEventsAsync/ReleaseOptions
await client.AcknowledgeCloudEventsAsync(topicName, eventSubscriptionName, new AcknowledgeOptions([<lock token obtained from the received cloud event>]));

Additional information

• As mentioned above, the EventGridPublisherClient requires an authentication mechanism, but the actual value is ignored by the emulator. You can use any value you want.
• Using TokenCredential (Azure Identity) instead of an access key requires the emulator to be running on HTTPS. The EventGridPublisherClient will throw an exception otherwise.
• The Event Grid validation mechanism is not implemented in the emulator. You can send events without having to validate your webhooks. This is because the emulator is not meant to be used in a production environment.
• The emulator tries to replicate the original Event Grid behavior when it comes to retry and HTTP header values. However, it is not guaranteed to be 100% accurate. If you find a bug, please open an issue.
• There's no persistence layer in the emulator, the messages are stored in memory. If you restart the emulator, all pending messages will be lost.

License

This code is licensed under the Apache License, Version 2.0. You may obtain a copy of this license at https://github.com/gsoft-inc/workleap-license/blob/main/LICENSE.