Event Grid for event-driven architecture in Azure - Step-by-Step Execution

Process Flow - Event Grid for event-driven architecture

Event Source emits event

↓

Event Grid receives event

↓

Event Grid filters and routes event

↓

Event Handler receives event

↓

Event Handler processes event

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Optional: Event Handler sends response or triggers next event

Events are sent from a source to Event Grid, which routes them to subscribed handlers for processing.

Execution Sample

Azure

1. Event Source sends event
2. Event Grid receives and routes
3. Event Handler processes event

This flow shows how an event moves from source through Event Grid to a handler.

Process Table

Step	Action	Event State	Routing Decision	Handler Response
1	Event Source emits event	Event created	Not yet routed	No response
2	Event Grid receives event	Event received	Evaluates filters	No response
3	Event Grid routes event	Event routed to handler	Matches subscription	No response
4	Event Handler receives event	Event in handler	Processing started	No response yet
5	Event Handler processes event	Event processed	Handled successfully	Response or trigger sent
6	End	No new events	No routing	Process complete

💡 Event processed and handled; no further routing needed.

Status Tracker

Variable	Start	After Step 2	After Step 3	After Step 5	Final
Event State	Created	Received	Routed	Processed	Handled
Routing Decision	None	Evaluating	Matched	Handled	Complete
Handler Response	None	None	None	Sent	Complete

Key Moments - 3 Insights

Why does Event Grid evaluate filters before routing?

Event Grid uses filters to decide which handlers should receive the event, as shown in step 2 and 3 of the execution_table.

What happens if no subscription matches the event?

If no subscription matches, Event Grid does not route the event to any handler, so processing stops after step 2 or 3.

Does the event handler send a response back to Event Grid?

Typically, the handler processes the event and may trigger other actions, but Event Grid does not require a response; see step 5.

Visual Quiz - 3 Questions

Look at the execution_table, what is the event state after Event Grid routes the event?

A Created

B Routed

C Received

D Processed

💡 Hint

Check the 'Event State' column at step 3 in the execution_table.

At which step does the event handler start processing the event?

A Step 4

B Step 3

C Step 2

D Step 5

💡 Hint

Look at the 'Action' column in the execution_table where processing starts.

If no subscription matches the event, what would change in the execution_table?

A Event handler processes event anyway

B Event would be routed to a default handler

C Routing Decision would be 'No match' and no handler response

D Event Grid retries routing

💡 Hint

Refer to the 'Routing Decision' and 'Handler Response' columns in steps 2 and 3.

Concept Snapshot

Event Grid routes events from sources to handlers.
It filters events based on subscriptions.
Handlers process events asynchronously.
No response is required back to Event Grid.
This enables scalable event-driven apps.

Full Transcript

Event Grid acts as a central hub for events. An event source sends an event to Event Grid. Event Grid receives the event and checks filters to decide which handlers should get it. If a subscription matches, Event Grid routes the event to the handler. The handler processes the event and may trigger further actions. This flow allows building scalable, loosely coupled applications where components communicate via events.

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