Why Event Grid for event-driven architecture in Azure? - Purpose & Use Cases

The Big Idea

What if your apps could instantly talk to each other without you writing endless connection code?

The Scenario

Imagine you have many different apps and services that need to talk to each other whenever something important happens, like a new file uploaded or a user signed up.

You try to connect each app directly to every other app by writing lots of code to check and send messages manually.

The Problem

This manual way is slow and confusing because you have to write and maintain tons of code for every connection.

If one app changes, you must update all the others too, which leads to mistakes and delays.

The Solution

Event Grid acts like a smart mailroom that automatically delivers messages (events) to the right apps without you writing extra code for each connection.

It listens for events and sends them instantly to any service that wants to know, making everything faster and simpler.

Before vs After

✗ Before

if new_file_uploaded:
    notify_service_a()
    notify_service_b()
    notify_service_c()

✓ After

event_grid.subscribe('new_file_uploaded', service_a)
event_grid.subscribe('new_file_uploaded', service_b)
event_grid.subscribe('new_file_uploaded', service_c)

What It Enables

It enables apps to react instantly and independently to events, creating flexible and scalable systems that grow easily.

Real Life Example

When a customer places an order online, Event Grid can instantly notify the billing system, the warehouse, and the shipping service without any extra coding for each step.

Key Takeaways

Manual event handling is complex and error-prone.

Event Grid automates event delivery to multiple services.

This creates faster, simpler, and scalable event-driven systems.

Practice

1. What is the main purpose of Azure Event Grid in event-driven architecture?

easy

A. To store large amounts of data for analytics

B. To connect event sources to event handlers for instant reactions

C. To create virtual machines automatically

D. To manage user identities and access

Solution

1. Step 1: Understand Event Grid's role

   Event Grid is designed to route events from sources to handlers quickly and efficiently.

2. Step 2: Compare options with Event Grid's function

   Only To connect event sources to event handlers for instant reactions describes connecting event sources to handlers for instant reactions, which matches Event Grid's purpose.

3. Final Answer:

   To connect event sources to event handlers for instant reactions -> Option B

4. Quick Check:

   Event routing = Connect sources to handlers [OK]

Hint: Event Grid routes events instantly between sources and handlers [OK]

Common Mistakes:

• Confusing Event Grid with data storage services
• Thinking Event Grid manages virtual machines
• Mixing Event Grid with identity management

2. Which Azure CLI command correctly creates an Event Grid subscription named mySub for a topic myTopic?

easy

A. az eventgrid event-subscription create --name mySub --source-resource-id /subscriptions/{subId}/resourceGroups/{rg}/providers/Microsoft.EventGrid/topics/myTopic

B. az eventgrid event-subscription create --name mySub --source-resource-id myTopic

C. az eventgrid topic create --name mySub --resource-group myTopic

D. az eventgrid subscription create --topic myTopic --name mySub

Solution

1. Step 1: Identify correct CLI syntax for event subscription creation

   The command requires the full resource ID for the source topic, not just the name.

2. Step 2: Analyze options for correct parameters

   az eventgrid event-subscription create --name mySub --source-resource-id /subscriptions/{subId}/resourceGroups/{rg}/providers/Microsoft.EventGrid/topics/myTopic uses the full resource ID format, which is required. az eventgrid event-subscription create --name mySub --source-resource-id myTopic uses only the topic name, which is invalid. Options C and D use incorrect commands or parameters.

3. Final Answer:

   az eventgrid event-subscription create --name mySub --source-resource-id /subscriptions/{subId}/resourceGroups/{rg}/providers/Microsoft.EventGrid/topics/myTopic -> Option A

4. Quick Check:

   Full resource ID needed for source in CLI [OK]

Hint: Use full resource ID for source in event-subscription create [OK]

Common Mistakes:

• Using only topic name instead of full resource ID
• Confusing topic creation with subscription creation
• Using wrong CLI commands like 'subscription create'

3. Given this Azure CLI command:

az eventgrid event-subscription create --name sub1 --source-resource-id /subscriptions/123/resourceGroups/rg1/providers/Microsoft.EventGrid/topics/topic1 --endpoint https://myapp.com/api/events

What happens after running this command?

medium

A. The endpoint URL is registered as a new event source

B. A new Event Grid topic named 'sub1' is created

C. An event subscription named 'sub1' is created to send events from 'topic1' to the specified endpoint

D. The command fails due to missing resource group parameter

Solution

1. Step 1: Understand the command purpose

   The command creates an event subscription named 'sub1' for the existing topic 'topic1'.

2. Step 2: Analyze the effect of parameters

   The endpoint URL is where events will be delivered. The command does not create a topic or register an endpoint as a source.

3. Final Answer:

   An event subscription named 'sub1' is created to send events from 'topic1' to the specified endpoint -> Option C

4. Quick Check:

   Event subscription sends events to endpoint [OK]

Hint: Event subscription links topic events to endpoint URL [OK]

Common Mistakes:

• Thinking the command creates a new topic
• Assuming endpoint is an event source
• Believing resource group is mandatory in this command

4. You wrote this Azure CLI command to create an Event Grid subscription:

az eventgrid event-subscription create --name sub2 --source-resource-id myTopic --endpoint https://myapp.com/api/events

But it fails with an error. What is the most likely cause?

medium

A. The source resource ID must be a full Azure resource ID, not just the topic name

B. The endpoint URL must be an Azure service URL

C. The subscription name cannot contain numbers

D. The command requires a resource group parameter

Solution

1. Step 1: Check the source-resource-id parameter format

   The source-resource-id must be the full Azure resource ID, not just the topic name.

2. Step 2: Validate other parameters

   The endpoint can be any valid HTTPS URL. Subscription names can include numbers. Resource group is not required here if full resource ID is used.

3. Final Answer:

   The source resource ID must be a full Azure resource ID, not just the topic name -> Option A

4. Quick Check:

   Full resource ID needed for source-resource-id [OK]

Hint: Always use full resource ID for source-resource-id [OK]

Common Mistakes:

• Using only topic name instead of full resource ID
• Thinking endpoint must be Azure URL
• Believing subscription names cannot have numbers

5. You want to build an app that reacts instantly when a new blob is uploaded to Azure Storage. Which Event Grid setup is best to achieve this?

hard

A. Create an Event Grid subscription on the Storage Account's blob deleted event

B. Create a Storage Queue and poll it every minute for new blobs

C. Use Azure Functions timer trigger to check blobs hourly

D. Create an Event Grid subscription on the Storage Account's blob created event, with your app's webhook as endpoint

Solution

1. Step 1: Identify event source and event type

   The Storage Account emits blob created events when new blobs upload.

2. Step 2: Choose subscription and endpoint

   Creating an Event Grid subscription for blob created events with your app's webhook endpoint enables instant reaction.

3. Step 3: Evaluate other options

   Polling or timer triggers cause delays. Subscribing to blob deleted events does not detect new uploads.

4. Final Answer:

   Create an Event Grid subscription on the Storage Account's blob created event, with your app's webhook as endpoint -> Option D

5. Quick Check:

   Blob created event subscription = instant reaction [OK]

Hint: Subscribe to blob created events for instant upload notifications [OK]

Common Mistakes:

• Using polling instead of event-driven subscription
• Subscribing to wrong event type like blob deleted
• Relying on timer triggers causing delays