Event Grid subscriptions and filters in Azure - Step-by-Step Execution

Process Flow - Event Grid subscriptions and filters

Event Published

↓

Event Grid Topic

↓

Subscription Filter Check

↓

Send Event

↓

Event Delivered to Subscriber

Events are published to a topic, then each subscription checks filters. If filters match, event is sent to subscriber; otherwise, it is dropped.

Execution Sample

Azure

1. Create Event Grid Topic
2. Create Subscription with filter on eventType = 'orderCreated'
3. Publish event with eventType 'orderCreated'
4. Event delivered to subscriber
5. Publish event with eventType 'orderCancelled'
6. Event dropped (filter mismatch)

This sequence shows how Event Grid delivers events only to subscriptions whose filters match the event.

Process Table

Step	Event Type	Filter Condition	Filter Match?	Action	Result
1	orderCreated	eventType == 'orderCreated'	Yes	Send Event	Event delivered to subscriber
2	orderCancelled	eventType == 'orderCreated'	No	Drop Event	Event not delivered

💡 No more events to process

Status Tracker

Variable	Start	After Step 1	After Step 2	Final
eventType	none	orderCreated	orderCancelled	orderCancelled
filterCondition	eventType == 'orderCreated'	unchanged	unchanged	unchanged
filterMatch	false	true	false	false

Key Moments - 2 Insights

Why does the event with type 'orderCancelled' not reach the subscriber?

Because the subscription filter only allows events where eventType equals 'orderCreated'. The execution_table row 2 shows filterMatch is No, so the event is dropped.

Can multiple subscriptions with different filters receive the same event?

Yes. Each subscription independently checks its filter. If multiple filters match the event, all those subscriptions receive it. This is implied by the filter check step in the concept_flow.

Visual Quiz - 3 Questions

Look at the execution_table, what is the filterMatch value at Step 1?

A Unknown

B No

C Yes

D False

💡 Hint

Check the 'Filter Match?' column in execution_table row for Step 1

At which step does the event get dropped due to filter mismatch?

A Step 1

B Step 2

C No event is dropped

D Both steps

💡 Hint

Look at the 'Action' column in execution_table to find when 'Drop Event' happens

If the filter condition changed to allow 'orderCancelled' events, what would happen at Step 2?

A Event would be delivered

B Event would be dropped

C No change

D Subscription would be deleted

💡 Hint

Refer to how filterMatch affects Action in execution_table rows

Concept Snapshot

Event Grid subscriptions receive events from topics.
Subscriptions use filters to decide which events to get.
If event matches filter, it is delivered.
If not, event is dropped.
Filters can be on eventType or other properties.
Multiple subscriptions can receive the same event if filters match.

Full Transcript

Event Grid works by sending events from a topic to subscribers. Each subscriber has a subscription with filters. When an event is published, Event Grid checks each subscription's filter. If the event matches the filter, it is sent to the subscriber. Otherwise, it is dropped. For example, a subscription filtering on eventType 'orderCreated' will receive only those events. Events with other types like 'orderCancelled' will be ignored by that subscription. This filtering helps subscribers get only relevant events.