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Azure Event Grid is an eventing backplane that enables event-driven, reactive programming.
It uses the publish-subscribe model.
Publishers emit events, but have no expectation about how the events are handled.
Subscribers decide on which events they want to handle.
It is strongly recommended to use available messaging products and services that support a publish-subscribe model, rather than building your own.
In Azure, consider using Service Bus, Event Hubs or Event Grid.
Other technologies that can be used for pub/sub messaging include Redis, RabbitMQ, and Apache Kafka.
First, select the Azure resource you would like to subscribe to, and then give the event handler or WebHook endpoint to send the event to.
Event Grid has built-in support for events coming from Azure services, like storage blobs and resource groups.
Event Grid also has support for your own events, using custom topics.
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Events - What happened.
An event is the smallest amount of information that fully describes something that happened in the system.
Every event has common information like: source of the event, time the event took place, and unique identifier.
Every event also has specific information that is only relevant to the specific type of event.
An event of size up to 64 KB is covered by General Availability (GA) Service Level Agreement (SLA).
The support for an event of size up to 1 MB is currently in preview. Events over 64 KB are charged in 64-KB increments.
Event sources - Where the event took place.
Your application is the event source for custom events that you define.
Event sources are responsible for sending events to Event Grid.
Topics - The endpoint where publishers send events.
The publisher creates the event grid topic, and decides whether an event source needs one topic or more than one topic.
A topic is used for a collection of related events.
System topics are built-in topics provided by Azure services.
You don't see system topics in your Azure subscription because the publisher owns the topics, but you can subscribe to them.
To subscribe, you provide information about the resource you want to receive events from.
As long as you have access to the resource, you can subscribe to its events.
Custom topics are application and third-party topics.
When you create or are assigned access to a custom topic, you see that custom topic in your subscription.
Event subscriptions - The endpoint or built-in mechanism to route events, sometimes to more than one handler.
Subscriptions are also used by handlers to intelligently filter incoming events.
A subscription tells Event Grid which events on a topic you're interested in receiving.
When creating the subscription, you provide an endpoint for handling the event.
You can filter the events that are sent to the endpoint. You can filter by event type, or subject pattern.
Event handlers - The app or service reacting to the event.
From an Event Grid perspective, an event handler is the place where the event is sent.
The handler takes some further action to process the event.
You can use a supported Azure service or your own webhook as the handler.
Depending on the type of handler, Event Grid follows different mechanisms to guarantee the delivery of the event.
For HTTP webhook event handlers, the event is retried until the handler returns a status code of
200 – OK.For Azure Storage Queue, the events are retried until the Queue service successfully processes the message push into the queue.
You can authenticate clients that publish events to Azure Event Grid topics, domains, partner namespaces using access key or Shared Access Signature (SAS) token.
For more information, see Using access keys or using Shared Access Signatures (SAS).
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Event schemas
Events consist of a set of four required string properties.
The properties are common to all events from any publisher.
The data object has properties that are specific to each publisher.
Event sources send events to Azure Event Grid in an array, which can have several event objects.
When posting events to an event grid topic, the array can have a total size of up to 1 MB.
Each event in the array is limited to 1 MB.
If an event or the array is greater than the size limits, you receive the response
413 Payload Too Large.Operations are charged in 64 KB increments though.
So, events over 64 KB will incur operations charges as though they were multiple events.
Event Grid sends the events to subscribers in an array that has a single event.
You can find the JSON schema for the Event Grid event and each Azure publisher's data payload in the Event Schema store
Properties that are used by all event publisher
For custom topics, the event publisher determines the data object.
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you can manually validate the subscription by sending a GET request to the validation URL.
The event subscription stays in a pending state until validated.
The validation Url uses port 553. If your firewall rules block port 553 then rules may need to be updated for successful manual handshake.
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Azure Service Bus to Event Grid integration overview
Service Bus can now emit events to Event Grid when there are messages in a queue or a subscription when no receivers are present.
You can create Event Grid subscriptions to your Service Bus namespaces, listen to these events, and then react to the events by starting a receiver.
With this feature, you can use Service Bus in reactive programming models.
The key scenario of this feature is that Service Bus queues or subscriptions with a low volume of messages do not need to have a receiver that polls for messages continuously.
To enable the feature, you need the following items:
A Service Bus Premium namespace with at least one Service Bus queue or a Service Bus topic with at least one subscription.
Contributor access to the Service Bus namespace.
An Event Grid subscription for the Service Bus namespace.
This subscription receives a notification from Event Grid that there are messages to be picked up.
Typical subscribers could be the Logic Apps feature of Azure App Service, Azure Functions, or a webhook contacting a web app.
The subscriber then processes the messages.
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Microsoft.EventGrid eventSubscriptions Template
| Code Block |
|---|
"destination": {
"endpointType": "string"
// For remaining properties, see EventSubscriptionDestination objects
}, |
endpointType: