Why Event Grid subscriptions and filters in Azure? - Purpose & Use Cases

The Big Idea

What if your system could instantly ignore noise and only hear what truly matters?

The Scenario

Imagine you have many different devices sending alerts to your system, and you want to respond only to specific types of alerts. Without filters, you have to check every alert manually to decide what to do.

The Problem

Manually sorting through all alerts is slow and tiring. It's easy to miss important messages or waste time on irrelevant ones. As the number of alerts grows, this becomes overwhelming and error-prone.

The Solution

Event Grid subscriptions with filters automatically send only the alerts you care about to the right place. This means your system reacts faster and only to relevant events, without extra work.

Before vs After

✗ Before

Receive all events
Check event type in code
Process or ignore manually

✓ After

Create subscription with filter
Only matching events are delivered
Process events directly

What It Enables

You can build smart, efficient systems that respond instantly to just the right events, saving time and reducing mistakes.

Real Life Example

A company uses Event Grid filters to send only "order placed" events to their billing system, while "order shipped" events go to the shipping team automatically.

Key Takeaways

Manual event handling is slow and error-prone.

Filters in Event Grid subscriptions automate event delivery.

This leads to faster, more reliable, and focused event processing.

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