🏁 Azure Event Grid

Serverless event routing at scale — react to state changes across Azure and custom sources

Table of Contents

  1. Product Overview
  2. Core Concepts
    1. Events vs Messages
    2. Topics
    3. Subscriptions
    4. Delivery Guarantee
  3. Event Schema
  4. Filtering
  5. SKU / Tiers
  6. SLA
  7. Security
  8. Integration with Azure Services
  9. Common Exam Scenarios

Product Overview

Azure Event Grid is a fully managed event routing service that uses a publish/subscribe model to deliver events (lightweight notifications of state changes) to subscribers in near real time. Unlike Service Bus and Storage Queues — which deal with messages containing data to be processed — Event Grid deals with events that announce something has happened.

Event Grid is the backbone of event-driven architecture on Azure, enabling serverless triggers, reactive automation, and integration between Azure services without polling.

flowchart LR
    subgraph Sources["Event Sources (Publishers)"]
        BS["Blob Storage\n(BlobCreated)"]
        RG["Resource Groups\n(ResourceWriteSuccess)"]
        CT["Custom Topic\n(your application)"]
        EH["Event Hubs\n(Capture complete)"]
    end
    subgraph EG["Azure Event Grid"]
        T1["System Topic\n(Azure service events)"]
        T2["Custom Topic\n(app events)"]
        D["Event Domain\n(multi-tenant topics)"]
    end
    subgraph Handlers["Event Handlers (Subscribers)"]
        F["Azure Functions"]
        WH["Webhook / Logic Apps"]
        SB["Service Bus Queue/Topic"]
        EHO["Event Hubs"]
        SQ["Storage Queue"]
        APIM["Azure API Management"]
    end
    BS --> T1
    RG --> T1
    CT --> T2
    T1 --> F
    T1 --> WH
    T2 --> SB
    T2 --> EHO
    T2 --> SQ

Core Concepts

Events vs Messages

  Event Message
Definition Lightweight notification of a state change Data to be processed or transferred
Payload Small (default max 1 MB) Larger (Service Bus up to 100 MB)
Consumption Any number of subscribers react Typically one consumer per message
Examples BlobCreated, VM deleted, custom order placed Order body, file content, payment details

⚠️ Exam Caveat: Event Grid sends events, not full message payloads. If the scenario involves large data transfer or guaranteed processing by exactly one consumer, the answer is Service Bus or Storage Queues, not Event Grid.

Topics

Topic Type Description
System Topics Built-in topics for Azure services (Blob, Resource Groups, Event Hubs, etc.)
Custom Topics User-defined topics for application-generated events
Partner Topics Events from third-party SaaS partners (e.g., Auth0, SAP, Tribal)
Event Domains Namespace for managing thousands of topics (multi-tenant SaaS scenarios)

Subscriptions

An event subscription defines:

  1. Endpoint (handler) — where to deliver events
  2. Filter rules — which events to receive (by type, subject prefix/suffix, or advanced JSON filter)
  3. Retry policy — how many retries and for how long
  4. Dead-lettering — where to send undeliverable events (a Storage Blob container)

Delivery Guarantee

Property Detail
Delivery model At-least-once
Ordering NOT guaranteed
Retry policy Exponential backoff, up to 24 hours / 30 retries
Dead-lettering ✅ To a Storage Blob container (not a queue)

⚠️ Exam Caveat: Event Grid delivers at-least-once with no ordering guarantee. Dead-lettered events go to a Storage Blob container — not a Service Bus DLQ.

Event Schema

Events conform to a standard schema (Event Grid Schema or CloudEvents 1.0):

{
  "id": "abc-123",
  "eventType": "Microsoft.Storage.BlobCreated",
  "subject": "/blobServices/default/containers/mycontainer/blobs/myfile.txt",
  "eventTime": "2026-03-01T12:00:00Z",
  "data": {
    "api": "PutBlob",
    "url": "https://mystorage.blob.core.windows.net/mycontainer/myfile.txt"
  },
  "dataVersion": "1.0"
}
Field Purpose
id Unique event identifier
eventType Routing and filtering key
subject Resource path (supports prefix/suffix filters)
data Event-specific payload (up to 1 MB total event size)

Filtering

Event Grid supports three filter types on subscriptions:

Filter Type Example
Event type Microsoft.Storage.BlobCreated only
Subject prefix/suffix Subject starts with /blobServices/default/containers/images/
Advanced filters JSON path comparisons (data.size > 1000)

SKU / Tiers

Tier Notes
Basic Per-event pricing; default for custom topics and system topics
Standard (namespace topics) Higher throughput, pull delivery model, MQTT support (preview)
Premium (namespace topics) VNet injection, private endpoints

⚠️ Exam Caveat: Classic Event Grid resources (system topics, custom topics) use a per-operation pricing model with no dedicated tier. The newer namespace topics (part of the Event Grid namespace resource) introduce Standard/Premium with pull delivery and MQTT — the exam may distinguish between these two resource models.

SLA

Resource Uptime SLA
Custom Topics 99.99%
System Topics 99.99%
Event Domains 99.99%

Event Grid has a higher baseline SLA (99.99%) than Service Bus Standard (99.9%) without requiring a premium tier.

Security

Mechanism Notes
Access keys Shared key for publishing to custom topics
SAS tokens Time-limited publish tokens
Microsoft Entra ID Preferred for event publishing from managed identities
Webhook validation Event Grid validates webhook endpoints via a handshake before delivering events
Private Endpoints Available on Event Grid namespace (Standard/Premium)
IP filtering Restrict inbound events to specific IP ranges
Managed Identity for delivery Event Grid can deliver events using a managed identity to downstream handlers

Integration with Azure Services

Event Source Events Published
Azure Blob Storage BlobCreated, BlobDeleted, BlobTierChanged
Azure Resource Manager Resource write/delete success/failure
Azure Container Registry Image pushed, image deleted, chart pushed
Azure Event Hubs Capture file created
Azure IoT Hub Device created, device deleted, telemetry
Azure Machine Learning Run completed, model registered
Azure Maps Geofence events
Azure Service Bus Active message count threshold (via Monitor)

Common Exam Scenarios

Scenario Answer
Trigger a Function when a blob is uploaded Event Grid system topic (BlobCreated → Function)
React to Azure resource changes (e.g., VM deleted) Event Grid (Resource Group system topic)
Route different events to different handlers Event Grid with subscription filters
Fan-out one event to many subscribers Event Grid topic with multiple subscriptions
Guaranteed ordering of events required NOT Event Grid → use Service Bus with Sessions
Event payload > 1 MB NOT Event Grid → use Service Bus or Event Hubs
Multi-tenant SaaS app sending per-customer events Event Domains
High-throughput telemetry stream (millions/sec) NOT Event Grid → use Event Hubs
Audit all resource changes across a subscription Event Grid (Azure Resource Manager system topic → Storage)
← 02 — Azure Storage Queues 04 — Azure Event Hubs →