Event Grid for event routing in Azure - Deep Dive

Overview - Event Grid for event routing

What is it?

Event Grid is a cloud service that helps move messages called events from one place to another automatically. It listens for events from sources like storage or apps and sends them to destinations like functions or webhooks. This helps different parts of a system talk to each other without waiting or checking constantly. It works like a smart mail sorter for digital messages.

Why it matters

Without Event Grid, systems would need to check repeatedly if something new happened, wasting time and resources. Event Grid makes communication fast and efficient by sending messages only when needed. This saves money, reduces delays, and helps build apps that react instantly to changes, like new files uploaded or user actions.

Where it fits

Before learning Event Grid, you should understand basic cloud concepts like events, messaging, and serverless functions. After mastering Event Grid, you can explore advanced event-driven architectures, integrate with other Azure services, and design scalable, reactive systems.

Mental Model

Core Idea

Event Grid is a smart messenger that listens for events and delivers them instantly to the right place without delay or waste.

Think of it like...

Imagine a postal service that only delivers letters when something important happens, like a package arriving or a bill due, instead of checking every house all the time. Event Grid is like that postal service for digital messages.

┌───────────────┐       ┌───────────────┐       ┌───────────────┐
│ Event Source  │──────▶│  Event Grid   │──────▶│ Event Handler │
│ (e.g., Blob  )│       │ (Router/Hub)  │       │ (e.g., Azure  │
│               │       │               │       │ Function)     │
└───────────────┘       └───────────────┘       └───────────────┘

Build-Up - 6 Steps

1

Foundation

Understanding Events and Event Sources

Concept: Learn what events are and where they come from in cloud systems.

An event is a message that says something happened, like a file uploaded or a user signed in. Event sources are places or services that create these events, such as Azure Blob Storage or custom apps. Events are small, simple, and describe the change or action.

Result

You can identify events and their sources in a cloud environment.

Understanding events and sources is key because Event Grid depends on these to know when to send messages.

2

Foundation

What is Event Routing in Cloud

Concept: Learn how events move from sources to handlers using routing.

Event routing means sending events from where they happen to where they are needed. Without routing, events would get lost or ignored. Routing decides which event goes to which service based on rules or filters.

Result

You grasp the basic flow of events through a system.

Knowing routing helps you see why Event Grid is important—it automates this flow efficiently.

3

Intermediate

How Event Grid Routes Events

🤔Before reading on: do you think Event Grid sends all events to all handlers or only to specific ones? Commit to your answer.

Concept: Event Grid uses topics and subscriptions to route events selectively.

Event Grid organizes events into topics, which are like mailboxes for event types. Handlers subscribe to topics with filters to get only events they care about. This way, Event Grid sends each event only to the right handlers, saving resources and time.

Result

You understand selective event delivery using topics and subscriptions.

Understanding selective routing prevents overload and ensures handlers get relevant events only.

4

Intermediate

Event Grid Integration with Azure Services

🤔Before reading on: do you think Event Grid works only with Azure services or can it connect to custom apps? Commit to your answer.

Concept: Event Grid connects both Azure services and custom event sources or handlers.

Event Grid supports many Azure services as event sources and handlers, like Blob Storage, Event Hubs, and Functions. It also allows custom apps to send or receive events using HTTP endpoints. This flexibility helps build complex, reactive systems.

Result

You see how Event Grid fits into the Azure ecosystem and beyond.

Knowing Event Grid’s broad integration options helps design flexible, scalable systems.

5

Advanced

Event Filtering and Advanced Routing

🤔Before reading on: do you think Event Grid can filter events by content or only by event type? Commit to your answer.

Concept: Event Grid can filter events by properties inside the event, not just by type.

Event Grid supports advanced filters that look inside event data, like filtering events where file size is over a limit or a specific user triggered the event. This reduces unnecessary processing and improves efficiency.

Result

You can create precise event routing rules based on event content.

Understanding content-based filtering helps build smarter, cost-effective event-driven apps.

6

Expert

Event Grid’s Scalability and Reliability Internals

🤔Before reading on: do you think Event Grid guarantees event delivery even if handlers are temporarily down? Commit to your answer.

Concept: Event Grid is designed to scale massively and ensure reliable event delivery with retries and dead-lettering.

Event Grid uses a distributed architecture to handle millions of events per second. It retries sending events if handlers fail and can store undelivered events in dead-letter queues for later inspection. This design ensures no event is lost and systems stay responsive.

Result

You appreciate Event Grid’s robustness and how it supports large, critical systems.

Knowing Event Grid’s reliability mechanisms helps design fault-tolerant, production-ready event systems.

Under the Hood

Event Grid works by receiving events from sources via HTTP or SDK calls. It stores events temporarily and matches them against subscriptions with filters. Then it pushes events to handlers using HTTP POST requests. It tracks delivery status and retries failed deliveries. Internally, it uses a distributed, multi-tenant system to scale and isolate workloads.

Why designed this way?

Event Grid was built to solve the inefficiency of polling and the complexity of custom event routing. Using a push model with filtering and retries balances speed, reliability, and cost. Alternatives like polling waste resources, and simpler routers lack filtering or scale.

┌───────────────┐       ┌───────────────┐       ┌───────────────┐
│ Event Source  │──────▶│  Event Grid   │──────▶│ Event Handler │
│ (HTTP/SDK)   │       │ (Filter &     │       │ (HTTP POST)   │
│               │       │  Routing)     │       │               │
└───────────────┘       └───────────────┘       └───────────────┘
         │                      │                      ▲
         │                      │                      │
         │                      ▼                      │
         │               ┌───────────────┐            │
         │               │ Dead-letter   │────────────┘
         │               │ Storage       │
         │               └───────────────┘

Myth Busters - 4 Common Misconceptions

Quick: Does Event Grid guarantee event order delivery? Commit to yes or no before reading on.

Common Belief: Event Grid always delivers events in the exact order they were generated.

Reality: Event Grid does not guarantee strict ordering of events; events may arrive out of order.

Why it matters: Assuming order can cause bugs in systems that depend on sequence, leading to incorrect processing or data corruption.

Quick: Can Event Grid replace all messaging systems like queues? Commit to yes or no before reading on.

Common Belief: Event Grid can be used as a full replacement for all message queue systems.

Reality: Event Grid is designed for event routing and notification, not for message queuing or complex workflows requiring message persistence and ordering.

Why it matters: Using Event Grid where queues are needed can cause loss of messages or processing errors.

Quick: Is Event Grid free to use without limits? Commit to yes or no before reading on.

Common Belief: Event Grid is unlimited and free to use for any volume of events.

Reality: Event Grid has pricing based on the number of events and operations, with limits on throughput per region.

Why it matters: Ignoring costs can lead to unexpected charges and scaling issues.

Quick: Can Event Grid deliver events to any protocol like FTP or SMTP? Commit to yes or no before reading on.

Common Belief: Event Grid can send events to any protocol or service directly.

Reality: Event Grid delivers events only via HTTP endpoints or Azure services; other protocols require additional integration.

Why it matters: Expecting unsupported protocols causes integration failures and delays.

Expert Zone

1

Event Grid’s retry policy uses exponential backoff with jitter to avoid overwhelming handlers during outages.

2

Dead-lettering stores undelivered events separately, allowing manual inspection and replay, critical for debugging production issues.

3

Event Grid supports custom event schemas and CloudEvents standard, enabling interoperability across diverse systems.

When NOT to use

Avoid Event Grid when you need guaranteed message ordering, complex workflows, or transactional message processing. Use Azure Service Bus or Event Hubs instead for those scenarios.

Production Patterns

In production, Event Grid is often paired with Azure Functions for serverless processing, Logic Apps for orchestration, and Azure Monitor for event tracking. It is used to build reactive microservices, automate workflows, and integrate SaaS apps.

Connections

Publish-Subscribe Messaging

Event Grid implements a publish-subscribe pattern where sources publish events and handlers subscribe to them.

Understanding publish-subscribe helps grasp how Event Grid decouples event producers and consumers for scalable systems.

Reactive Programming

Event Grid enables reactive programming by pushing events to handlers that react immediately.

Knowing reactive programming concepts clarifies how Event Grid supports real-time, event-driven applications.

Postal Delivery Systems

Event Grid’s event routing is similar to postal systems sorting and delivering mail based on addresses and rules.

Studying postal logistics reveals principles of routing, filtering, and retrying that apply to Event Grid’s design.

Common Pitfalls

#1 Assuming Event Grid guarantees event order and building logic that depends on it.

Wrong approach:

Process events in the order received without checking timestamps or sequence numbers.

Correct approach:

Design event handlers to be idempotent and handle out-of-order events gracefully using event metadata.

Root cause:

Misunderstanding Event Grid’s delivery model and lack of ordering guarantees.

#2 Using Event Grid for long-term message storage or complex workflows.

Wrong approach:

Rely on Event Grid to hold events until processed, expecting guaranteed delivery and ordering.

Correct approach:

Use Azure Service Bus or Event Hubs for durable messaging and workflow management.

Root cause:

Confusing event routing with message queuing and workflow orchestration.

#3 Not setting up dead-lettering or monitoring for failed event deliveries.

Wrong approach:

Ignore failed event deliveries and assume all events are processed successfully.

Correct approach:

Configure dead-letter destinations and monitor Event Grid metrics to catch and handle failures.

Root cause:

Overlooking the need for operational visibility and error handling in event-driven systems.

Key Takeaways

Event Grid is a cloud service that routes events from sources to handlers efficiently and selectively.

It uses topics and subscriptions with filters to deliver only relevant events, saving resources.

Event Grid supports many Azure services and custom apps, enabling flexible event-driven architectures.

It does not guarantee event order and is not a replacement for message queues or workflows.

Understanding its design and limitations helps build reliable, scalable, and reactive cloud systems.

Practice

1. What is the main purpose of Azure Event Grid in cloud applications?

easy

A. To route events from sources to event handlers automatically

B. To store large amounts of data for analytics

C. To create virtual machines for compute power

D. To manage user identities and access control

Solution

1. Step 1: Understand Event Grid's role

   Event Grid is designed to route events from sources to handlers automatically, enabling reactive applications.

2. Step 2: Compare with other services

   Other options describe different Azure services: storage, compute, and identity management, not event routing.

3. Final Answer:

   To route events from sources to event handlers automatically -> Option A

4. Quick Check:

   Event routing = To route events from sources to event handlers automatically [OK]

Hint: Event Grid moves events, not data or users [OK]

Common Mistakes:

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

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

easy

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

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

C. az eventgrid topic create --name mySub --source myTopic

D. az eventgrid event-subscription create --name mySub --source-resource-id /subscriptions/.../resourceGroups/.../providers/Microsoft.EventGrid/topics/myTopic

Solution

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

   The command requires the full resource ID for the source topic using --source-resource-id.

2. Step 2: Evaluate options

   az eventgrid event-subscription create --name mySub --source-resource-id /subscriptions/.../resourceGroups/.../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 lacks full resource ID, C creates a topic not subscription, D uses wrong command.

3. Final Answer:

   az eventgrid event-subscription create --name mySub --source-resource-id /subscriptions/.../resourceGroups/.../providers/Microsoft.EventGrid/topics/myTopic -> Option D

4. Quick Check:

   Full resource ID needed for subscription creation [OK]

Hint: Use full resource ID with --source-resource-id for subscriptions [OK]

Common Mistakes:

• Using topic creation command instead of subscription
• Omitting full resource ID in source
• Using incorrect command names

3. Given this Azure CLI command output snippet for an Event Grid subscription:

{
  "destination": {
    "endpointType": "WebHook",
    "properties": {
      "endpointUrl": "https://myapp.com/api/events"
    }
  },
  "filter": {
    "subjectBeginsWith": "orders/",
    "subjectEndsWith": ".json"
  }
}

Which events will be delivered to the webhook endpoint?

medium

A. Only events with subjects exactly 'orders/.json'

B. All events regardless of subject

C. All events with subjects starting with 'orders/' and ending with '.json'

D. Events with subjects containing 'orders/' anywhere

Solution

1. Step 1: Understand subject filters in Event Grid

   The filter uses subjectBeginsWith and subjectEndsWith to select events whose subject starts with 'orders/' and ends with '.json'.

2. Step 2: Analyze options

   All events with subjects starting with 'orders/' and ending with '.json' matches the filter exactly. Only events with subjects exactly 'orders/.json' is too strict (exact match), C ignores filters, D is incorrect because 'contains' is not used.

3. Final Answer:

   All events with subjects starting with 'orders/' and ending with '.json' -> Option C

4. Quick Check:

   Subject filters = startsWith + endsWith [OK]

Hint: Filters combine start and end patterns, not exact or contains [OK]

Common Mistakes:

• Assuming exact subject match required
• Ignoring subject filters and expecting all events
• Confusing contains with beginsWith or endsWith

4. You created an Event Grid subscription but your webhook endpoint is not receiving events. Which of these is the most likely cause?

medium

A. The Event Grid topic does not exist

B. The webhook endpoint URL is incorrect or unreachable

C. You forgot to create an Azure Storage account

D. The subscription filter matches all events

Solution

1. Step 1: Check webhook endpoint accessibility

   If the webhook URL is wrong or the endpoint is down, events cannot be delivered.

2. Step 2: Evaluate other options

   Topic existence is important but usually checked at creation; storage account is unrelated; a filter matching all events would not block delivery.

3. Final Answer:

   The webhook endpoint URL is incorrect or unreachable -> Option B

4. Quick Check:

   Endpoint must be reachable for event delivery [OK]

Hint: Check webhook URL and network access first [OK]

Common Mistakes:

• Assuming storage account is needed for Event Grid
• Ignoring endpoint network issues
• Thinking filters block all events by default

5. You want to route events from multiple Azure Blob Storage accounts to a single Azure Function using Event Grid. What is the best approach to achieve this?

hard

A. Create an Event Grid subscription for each storage account, all pointing to the same Azure Function endpoint

B. Create one Event Grid subscription on one storage account and expect it to receive events from all accounts

C. Use Azure Logic Apps to poll each storage account and forward events to the function

D. Configure the Azure Function to listen directly to all storage accounts without Event Grid

Solution

1. Step 1: Understand Event Grid subscription scope

   Event Grid subscriptions are scoped to a single resource, so each storage account needs its own subscription.

2. Step 2: Evaluate options

   Create an Event Grid subscription for each storage account, all pointing to the same Azure Function endpoint correctly creates multiple subscriptions pointing to one function. Create one Event Grid subscription on one storage account and expect it to receive events from all accounts is invalid because one subscription cannot cover multiple accounts. Use Azure Logic Apps to poll each storage account and forward events to the function adds unnecessary polling. Configure the Azure Function to listen directly to all storage accounts without Event Grid is not supported as functions rely on Event Grid for event routing.

3. Final Answer:

   Create an Event Grid subscription for each storage account, all pointing to the same Azure Function endpoint -> Option A

4. Quick Check:

   One subscription per source resource [OK]

Hint: Each source needs its own subscription to route events [OK]

Common Mistakes:

• Assuming one subscription covers multiple sources
• Using polling instead of event-driven routing
• Expecting Azure Function to listen without Event Grid