Azure Event Grid Simulator

A simple simulator which provides endpoints that mimic the functionality of Azure Event Grid topics and subscribers and is compatible with the Microsoft.Azure.EventGrid client library.

Configuration

Topics and their subscribers are configured in the appsettings.json file. Alternatively, you can specify the configuration file to use by setting the ConfigFile command line argument, e.g.

AzureEventGridSimulator.exe --ConfigFile=/path/to/config.json

You can add multiple topics. Each topic must have a unique port. Each topic can have multiple subscribers. An example of one topic with one subscriber is shown below.

{
  "topics": [
    {
      "name": "MyAwesomeTopic",
      "port": 60101,
      "key": "TheLocal+DevelopmentKey=",
      "subscribers": [
        {
          "name": "LocalAzureFunctionSubscription",
          "endpoint": "http://localhost:7071/runtime/webhooks/EventGrid?functionName=PersistEventToDb",
          "disableValidation": true
        }
      ]
    }
  ]
}

Topic Settings

• name: The name of the topic. It can only contain letters, numbers, and dashes.
• port: The port to use for the topic endpoint. The topic will listen on https://0.0.0.0:{port}/.
• key: The key that will be used to validate the aeg-sas-key or aeg-sas-token header in each request. If this is not supplied then no key validation will take place.
• subscribers: The subscriptions for this topic.

Subscriber Settings

• name: The name of the subscriber. It can only contain letters, numbers, and dashes.
• endpoint: The subscription endpoint url. Events received by topic will be sent to this address.
• disableValidation:
  • false (the default) subscription validation will be attempted each time the simulator starts.
  • true to disable subscription validation.

Subscription Validation

When a subscription is added to Azure Event Grid it first sends a validation event to the subscription endpoint. The validation event contains a validationCode which the subscription endpoint must echo back. If this does not occur then Azure Event Grid will not enable the subscription. Azure Event Grid also supports manual validation via a validationUrl which is sent with the validationCode in the initial validation message.

More information about subscription validation can be found at https://docs.microsoft.com/en-us/azure/event-grid/security-authentication.

The Azure Event Grid Simualator can mimick this behaviour using the validationRequired setting.

• false (the default), subscription validation will be disabled.
• true, a subscription validation event will be sent to the subscriber when the simulator starts. The subscription will not accept events until it is successfully validated.

Filtering Events

Event filtering is configurable on each subscriber using the filter model defined here: https://docs.microsoft.com/en-us/azure/event-grid/event-filtering. This page provides a full guide to the configuration options available and all parts of this guide are currently supported. For ease of transition, explicit limitations have also been adhered to. The restrictions mentioned have been further modified (https://azure.microsoft.com/en-us/updates/advanced-filtering-generally-available-in-event-grid/) and these new less restrictive filtering limits have been observed.

Extending the example above to include a basic filter which will only deliver events to the subscription if they are of a specific type is illustrated below.

{
  "topics": [
    {
      "name": "MyAwesomeTopic",
      "httpsPort": 60101,
      "key": "TheLocal+DevelopmentKey=",
      "subscribers": [
        {
          "name": "LocalAzureFunctionSubscription",
          "endpoint": "http://localhost:7071/runtime/webhooks/EventGrid?functionName=PersistEventToDb",
          "filter": {
            "includedEventTypes": ["my.eventType"]
          }
        }
      ]
    }
  ]
}

This can be extended to allow subject filtering:

"filter": {
  "subjectBeginsWith": "/blobServices/default/containers/mycontainer/log",
  "subjectEndsWith": ".jpg",
  "isSubjectCaseSensitive": true
}

or advanced filtering:

"filter": {
  "advancedFilters": [
    {
      "operatorType": "NumberGreaterThanOrEquals",
      "key": "Data.Key1",
      "value": 5
    },
    {
      "operatorType": "StringContains",
      "key": "Subject",
      "values": ["container1", "container2"]
    }
  ]
}

Using the Simulator

Once configured and running, requests are posted to a topic endpoint. The endpoint of a topic will be in the form: https://localhost:<configured-port>/api/events?api-version=2018-01-01.

cURL Example

curl -k -H "Content-Type: application/json" -H "aeg-sas-key: TheLocal+DevelopmentKey=" -X POST "https://localhost:60101/api/events?api-version=2018-01-01" -d @Data.json

Data.json

[
  {
    "id": "8727823",
    "subject": "/example/subject",
    "data": {
      "MyProperty": "This is my awesome data!"
    },
    "eventType": "Example.DataType",
    "eventTime": "2019-01-01T00:00:00.000Z",
    "dataVersion": "1"
  }
]

Postman

An example request that you can import into Postman can be found in the AzureEventGridSimulator repo here https://github.com/pmcilreavy/AzureEventGridSimulator/blob/master/src/Azure%20Event%20Grid%20Simulator.postman_collection.json.

EventGridClient

var client = new EventGridClient(new TopicCredentials("TheLocal+DevelopmentKey="));
await client.PublishEventsWithHttpMessagesAsync(
    topicHostname: "localhost:60101",
    events: new List<EventGridEvent> { <your event> });

Notes

HTTPs

Azure Event Grid only accepts connections over https and so the simulator only supports https too. The simulator uses the dotnet development certificate to secure each topic port. You can ensure that this certifcate is installed and trusted by running the following command.

dotnet dev-certs https --trust

Subscribers

A topic can have 0 to n subscribers. When a request is received for a topic, the events will be forwarded to each of the subscribers with the addition of an aeg-event-type: Notification header. If the message contains multiple events, they will be sent to each subscriber one at a time inline with the Azure Event Grid behaviour. "Event Grid sends the events to subscribers in an array that has a single event. This behavior may change in the future." https://docs.microsoft.com/en-us/azure/event-grid/event-schema

Key Validation

The simulator supports both: aeg-sas-key or aeg-sas-token request headers. Using aeg-sas-key is the simplest way. Just set the value of the aeg-sas-key to the same key value configured for the topic. Using an aeg-sas-token is more secure as the key is hashed but it's a bit trickier to set up. More information on sas token can be found here https://docs.microsoft.com/en-us/azure/event-grid/security-authentication#sas-tokens.

If the incoming request contains either an aeg-sas-token or an aeg-sas-key header and there is a Key configured for the topic then the simulator will validate the key and reject the request if the value in the header is not valid. If you want to skip the validation then set the Key to null in appsettings.json.

Size Validation

Azure Event Grid imposes certain size limits to the overall message body and to the each individual event. The overall message body must be <= 1Mb and each individual event must be <= 64Kb. These are the advertised size limits. My testing has shown that the actual limits are 1.5Mb and 65Kb.

Message Validation

Ensures that the properties of each event meets the minimum requirements.

Field	Description
Id	Must be a string. Not null or whitespace.
Subject	Must be a string. Not null or whitespace.
EventType	Must be a string. Not null or whitespace.
EventTime	Must be a valid date/time.
MetadataVersion	Must be null or 1.
Topic	Leave null or empty. Event Grid will populate this field.
DataVersion	Optional. e.g. 1.
Data	Optional. Any custom object.

Why?

There are a couple of similar projects out there. What I found though is that they don't adequately simulate an actual Event Grid Topic endpoint.

Azure Event Grid only excepts connections over https and the Microsoft.Azure.EventGrid client only sends requests over https. If you're posting events to an Event Grid topic using custom code then maybe this isn't an issue. If you are using the client library though then any test endpoint must be https.

Typically an event grid topic endpoint url is like so: https://topic-name.location-name.eventgrid.azure.net/api/events. Note that all the information needed to post to a topic is contained in the host part. The Microsoft.Azure.EventGrid client will essentially reduce the url you give it down to just the host part and prefix it with https (regardless of the original scheme).

It posts the payload to https://host:port and drops the query uri. All of the existing simulator/ emulator projects I found don't support https and use a the query uri to distinguish between the topics. This isn't compatible with the Microsoft.Azure.EventGrid client.

Future Development

• Subscriber retries & dead lettering. https://docs.microsoft.com/en-us/azure/event-grid/delivery-and-retry
• Ceritifcate cofiguration in appsettings.json.
• Docker support.
• Maybe a web based console?