Event Grid subscriptions and filters in Azure - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an Event Grid subscription in Azure?

An Event Grid subscription connects an event source to an event handler. It tells Azure where to send events when they happen.

beginner

What is the purpose of filters in Event Grid subscriptions?

Filters let you choose which events to receive based on event properties, so you only get the events you care about.

intermediate

Name two types of filters you can use in Event Grid subscriptions.

You can use subject filters (to filter by event subject) and advanced filters (to filter by event data or system properties).

intermediate

How does a subject filter work in Event Grid?

A subject filter matches the event's subject string with a prefix, suffix, or exact match to decide if the event should be sent.

beginner

What happens if no filters are set on an Event Grid subscription?

If no filters are set, the subscription receives all events from the event source.

What does an Event Grid subscription do?

A Creates virtual machines

B Stores event data permanently

C Manages user access

D Connects an event source to an event handler

An Event Grid subscription connects an event source to an event handler to deliver events.

Which filter type allows filtering events by event subject prefix or suffix?

A Subject filter

B Advanced filter

C Time filter

D Location filter

Subject filters match event subjects using prefix, suffix, or exact match.

If you want to receive only events where a property 'status' equals 'completed', which filter would you use?

A Subject filter

B Subscription filter

C Advanced filter

D No filter

Advanced filters allow filtering by event data properties like 'status'.

What happens if you create an Event Grid subscription without any filters?

A No events are delivered

B All events from the source are delivered

C Only error events are delivered

D Subscription is invalid

Without filters, the subscription receives all events from the event source.

Which of these is NOT a valid filter type in Event Grid subscriptions?

A Time filter

B Advanced filter

C Subject filter

D Prefix filter

Time filter is not a filter type in Event Grid; subject and advanced filters are valid.

Explain how Event Grid subscriptions use filters to control event delivery.

Think about how you pick only certain messages from a mailbox.

Describe the difference between subject filters and advanced filters in Event Grid subscriptions.

One filters by the event's name, the other by event details.

Practice

1. What is the main purpose of using filters in Azure Event Grid subscriptions?

easy

A. To receive only specific events based on criteria like event type or subject

B. To increase the number of events sent to subscribers

C. To block all events from being delivered

D. To change the event data before delivery

Solution

1. Step 1: Understand Event Grid subscriptions

   Subscriptions let you receive events from Azure services.

2. Step 2: Role of filters in subscriptions

   Filters help select only the events you want, based on event type or subject.

3. Final Answer:

   To receive only specific events based on criteria like event type or subject -> Option A

4. Quick Check:

   Filters select events = B [OK]

Hint: Filters pick events you want, ignoring others [OK]

Common Mistakes:

• Thinking filters increase event volume
• Believing filters block all events
• Assuming filters modify event data

2. Which of the following is the correct JSON snippet to filter events by subject prefix in an Event Grid subscription?

easy

A. "filter": { "subjectBeginsWith": "/blobServices/default/containers/images" }

B. "filter": { "subjectEndsWith": "/blobServices/default/containers/images" }

C. "filter": { "eventType": "Microsoft.Storage.BlobCreated" }

D. "filter": { "subjectContains": "images" }

Solution

1. Step 1: Identify subject prefix filter syntax

   The correct property to filter by subject prefix is "subjectBeginsWith".

2. Step 2: Match the correct JSON snippet

   "filter": { "subjectBeginsWith": "/blobServices/default/containers/images" } uses "subjectBeginsWith" with the correct path prefix.

3. Final Answer:

   "filter": { "subjectBeginsWith": "/blobServices/default/containers/images" } -> Option A

4. Quick Check:

   Prefix filter uses subjectBeginsWith = A [OK]

Hint: Prefix filters use subjectBeginsWith property [OK]

Common Mistakes:

• Confusing subjectEndsWith with subjectBeginsWith
• Using eventType instead of subject filter
• Using subjectContains which is not valid

3. Given this Event Grid subscription filter configuration:

{ "subjectBeginsWith": "/devices/", "subjectEndsWith": "/temperature" }

Which event subject will be delivered to the subscriber?

medium

A. /sensors/device123/temperature

B. /devices/device123/humidity

C. /devices/device123/temperature

D. /devices/temperature/device123

Solution

1. Step 1: Understand filter conditions

   The event subject must start with "/devices/" and end with "/temperature".

2. Step 2: Check each option

   /devices/device123/temperature matches both start and end. Others fail one condition.

3. Final Answer:

   /devices/device123/temperature -> Option C

4. Quick Check:

   Subject starts with /devices/ and ends with /temperature = A [OK]

Hint: Match both start and end strings exactly [OK]

Common Mistakes:

• Ignoring subjectEndsWith condition
• Confusing similar paths
• Assuming partial matches are enough

4. You wrote this filter in your Event Grid subscription:

{ "subjectBeginsWith": "/orders/", "subjectEndsWith": "/completed" }

But no events are received even though events exist. What is the likely issue?

medium

A. The subscription is disabled

B. The filter syntax is invalid JSON

C. Event Grid does not support subject filters

D. The subject filter is case-sensitive and event subjects differ in case

Solution

1. Step 1: Check filter syntax and support

   The JSON syntax is valid and Event Grid supports subject filters.

2. Step 2: Consider case sensitivity and subscription status

   Subject filters are case-sensitive; if event subjects differ in case, no match occurs. Subscription being disabled would stop all events, but question implies filter issue.

3. Final Answer:

   The subject filter is case-sensitive and event subjects differ in case -> Option D

4. Quick Check:

   Subject filters are case-sensitive = D [OK]

Hint: Remember filters are case-sensitive in Event Grid [OK]

Common Mistakes:

• Assuming filters ignore case
• Blaming JSON syntax without checking
• Ignoring subscription status

5. You want to create an Event Grid subscription that only receives events of type Microsoft.Storage.BlobCreated where the blob is in the container named images. Which filter configuration achieves this?

hard

A. { "eventType": "Microsoft.Storage.BlobDeleted", "subjectBeginsWith": "/blobServices/default/containers/images/" }

B. { "eventType": "Microsoft.Storage.BlobCreated", "subjectBeginsWith": "/blobServices/default/containers/images/" }

C. { "eventType": "Microsoft.Storage.BlobCreated", "subjectEndsWith": "/images" }

D. { "eventType": "Microsoft.Storage.BlobCreated" }

Solution

1. Step 1: Filter by event type

   The event type must be exactly "Microsoft.Storage.BlobCreated" to get blob creation events.

2. Step 2: Filter by subject prefix for container

   The subject prefix for blobs in the "images" container is "/blobServices/default/containers/images/".

3. Step 3: Combine filters correctly

   { "eventType": "Microsoft.Storage.BlobCreated", "subjectBeginsWith": "/blobServices/default/containers/images/" } combines both eventType and subjectBeginsWith correctly.

4. Final Answer:

   { "eventType": "Microsoft.Storage.BlobCreated", "subjectBeginsWith": "/blobServices/default/containers/images/" } -> Option B

5. Quick Check:

   Event type and subject prefix filter combined = C [OK]

Hint: Combine eventType and subjectBeginsWith for precise filtering [OK]

Common Mistakes:

• Using wrong event type
• Using subjectEndsWith instead of subjectBeginsWith
• Omitting container path in subject filter