Azure Event Grid Domain vs Custom Topic for Scaling

AZ-204 By islever Editorial Last updated

Develop event-based solutions

Short answer

A Publishing events to an event domain meets the goal by providing a single endpoint for thousands of topics.

Question

Note: This question is part of a series of questions that present the same scenario. Each question in the series contains a unique solution that might meet the stated goals. Some question sets might have more than one correct solution, while others might not have a correct solution. After you answer a question in this section, you will NOT be able to return to it. As a result, these questions will not appear in the review screen. You are implementing an application by using Azure Event Grid to push near-real-time information to customers. You have the following requirements: • You must send events to thousands of customers that include hundreds of various event types. • The events must be filtered by event type before processing. • Authentication and authorization must be handled by using Microsoft Entra ID. • The events must be published to a single endpoint. You need to implement Azure Event Grid. Solution: Publish events to an event domain. Create a custom topic for each customer. Does the solution meet the goal?
  1. Yes Correct Answer
  2. No

Key Takeaways

The key insight is that Event Domains act as meta-topics providing a unified publishing endpoint, whereas creating a custom topic per customer would fail scalability and endpoint constraints.

This question tests the architectural decision between using Azure Event Domains and custom topics for high-scale event publishing. The solution meets the goal by leveraging domains to manage thousands of topics under a single endpoint.

Common mistake: Candidates often choose 'No' because they incorrectly believe that each customer requires a distinct custom topic or overlook the domain's ability to handle massive topic counts via its quota limits.

Expert Analysis

Why the Answer Is Correct

An Event Domain in Azure Event Grid is designed specifically to manage large numbers of related topics (up to 100,000) under a single management scope. It provides a single publishing endpoint for all topics within the domain, which satisfies the requirement to publish to a single endpoint while supporting thousands of customers. This architecture allows for efficient filtering and authorization at the topic or subscription level without needing separate endpoints per customer.

Why the Other Options Are Wrong

Choosing 'No' implies the solution is flawed, but the proposed design aligns with Microsoft's recommended pattern for scaling Event Grid. The alternative of creating a custom topic for each customer would be inefficient and harder to manage at scale, though technically possible; however, the domain approach explicitly solves the 'single endpoint' constraint more elegantly. Option B is incorrect because it fails to recognize the domain's purpose.

Community Comment Notes

Community feedback is split, with many users correctly identifying 'Yes' based on official documentation stating domains support up to 100,000 topics. Some users argue for 'No', citing that subscriptions are needed for filtering, but the solution description implies the necessary configuration exists. Others note that 'Domain Topics' are used within domains, not traditional custom topics, but this distinction does not invalidate the core benefit of the single endpoint and scalability.

Official Reference

https://learn.microsoft.com/en-us/azure/event-grid/event-domains?tabs=event-grid-event-schema

This link opens the official vendor documentation in a new tab.

Exam Strategy

When asked about scaling Event Grid for many customers, prioritize Event Domains over individual custom topics if a single publishing endpoint is required. Always check if the scenario mentions 'thousands' of entities or a need for centralized management.

Frequently Asked Questions

Why is an Event Domain better than a custom topic for this scenario?

Event Domains support up to 100,000 topics and provide a single publishing endpoint, making them ideal for managing thousands of customers efficiently.

Can I use Event Subscriptions for filtering with Event Domains?

Yes, you can create event subscriptions on domain topics to filter events by type before processing, meeting the filtering requirement.

More AZ-204 FAQ →

Community Votes

A
64%
B
36%

64% of anonymous learners picked answer A. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 11 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 11

  1. RDTAus 👍 8 Answered A
    https://learn.microsoft.com/en-us/azure/event-grid/event-domains?tabs=event-grid-event-schema An event domain is a management tool for large number of Event Grid topics related to the same application. You can think of it as a meta-topic that can have thousands of individual topics. It provides one publishing endpoint for all the topics in the domain. When publishing an event, the publisher must specify the target topic in the domain to which it wants to publish. The publisher can send an array or a batch of events where events are sent to different topics in the domain. See the Publishing events to an event domain section for details. Domains also give you authentication and authorization control over each topic so you can partition your tenants. This article describes how to use event domains to manage the flow of custom events to your various business organizations, customers, or applications.
  2. FeriAZ 👍 5 Answered B
    Creating a custom topic for each customer would be unnecessarily complex and not scalable for thousands of customers. It could also complicate the management and the goal of publishing events to a single endpoint.
  3. Junak 👍 4 Answered A
    Probably the answer is Yes. https://learn.microsoft.com/en-us/azure/event-grid/event-domains?tabs=event-grid-event-schema#example-use-case
  4. ProtossOR89144 👍 2 Answered A
    https://learn.microsoft.com/en-us/azure/event-grid/quotas-limits - "When the limit is reached, you can consider a different region or consider using domains, which can support 100,000 topics.", so the domain is a way to handle thousands of topics
  5. 5691024 👍 1 Answered B
    Event Domain is correct But I believe 'Custom Topic for each customer' is not. 1. Event Domains use "Domain Topics", not Custom Topics: See image: https://learn.microsoft.com/en-us/azure/event-grid/includes/media/domain-example-use-case/contoso-construction-example.png I don't think Domain Topics and Custom Topics are the same thing. It seems you can create an Event Subscription, which automatically creates the Domain Topic, or create Domain Topics manually, but these appear to be distinct from Custom Topics. See: https://learn.microsoft.com/en-us/azure/event-grid/event-domains?tabs=cloud-event-schema#subscribing-to-topics 2. Custom Topics are limited to 100 per Azure subscription, therefore the requirement of "thousands of customers" cannot be fufilled by Custom Topics. Therefore, the correct answer would be "use event domain" and "create Domain Topic for each customer" or "create Event Subscription for each customer"
Show 6 more comments
  1. Jobalos009 👍 1 Answered A
    The answer is A. An event domain provides an endpoint for thousands of individual topics related to the same application. You can think of it as a meta-topic that can have thousands of individual topics. It provides one publishing endpoint for all the topics in the domain. Ref: https://learn.microsoft.com/en-us/azure/event-grid/event-domains?tabs=cloud-event-schema
  2. overhill 👍 1 Answered B
    you create event domain, you create topics, but what about the subscriptions? they need to be subscribed I'm almost sure. so I would say this is a: NO
  3. overhill 👍 1
    you create event domain, you create topics, but what about the subscriptions? they need to be subscribed I'm almost sure. so I would say this is a no
  4. Vichu_1607 👍 1 Answered B
    No The correct approach is to use a single custom topic with event subscriptions and filters.
  5. examtopicsLogin123 👍 1 Answered A
    Got this question in February 2025. Went with "event domain"
  6. dom271219 👍 1 Answered B
    No. It sould be custom topic.

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