Event Grid Custom Topic for Thousands of Customers: Does It Meet the Goal?

Develop event-based solutions

Answer Correct answer: B — Custom topics allow at most 500 event subscriptions, so one subscription per customer cannot scale to thousands; use Event Grid domains instead.

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 a custom topic. Create an event subscription for each customer. Does the solution meet the goal?

Yes
No Correct Answer

Community Votes

67%

33%

67% of anonymous learners picked answer B. Votes are pick records left by other test-takers — they are not the verified answer.

Community Insight

The question tests Event Grid scalability limits versus feature support; the trap is selecting Yes (A) because event-type filtering and Microsoft Entra ID authentication are satisfied while the 500-subscriptions-per-custom-topic quota is missed.

This AZ-204 scenario tests whether publishing to an Azure Event Grid custom topic with one event subscription per customer meets requirements for thousands of customers. Because a custom topic supports only 500 event subscriptions, the correct answer is No (B), and Event Grid domains are the recommended fix.

Choosing Yes (A) because custom topics can filter events by type and integrate with Microsoft Entra ID, overlooking that the 500 event-subscription limit per custom topic cannot handle thousands of customers.

Community Discussion (5 comments)

FeriAZ 👍 2

Azure Event Grid Domains Event subscriptions within the domain can then be configured for each customer or customer group, with filtering rules applied to ensure that subscribers only receive the events that are relevant to them. This architecture effectively addresses the need for event filtering before processing.

egaws 👍 4 Selected: B

Custom topics per Azure subscription: 100 When the limit is reached, you can consider a different region or consider using domains, which can support 100,000 topics.

raymond_abcd 👍 3 Selected: B

The number of subscriptions per custom topic is limited to 500. See: https://learn.microsoft.com/en-us/azure/event-grid/quotas-limits#custom-topic-system-topic-and-partner-topic-resource-limits You have thousands of customers so you will not manage with this solution

FeriAZ 👍 1 Selected: B

Scalability and Management: Managing an event subscription for each customer could become cumbersome as the number of customers grows. This approach might not efficiently scale or simplify the management of event types and customer-specific filtering. Single Endpoint Requirement: Publishing events to a custom topic does meet the requirement of a single endpoint for publishing. However, the management and scalability of subscriptions could pose challenges. Filtering by Event Type: While event subscriptions can be configured to filter events based on type, the proposed solution might not be the most efficient way to handle hundreds of event types, especially if the filtering needs are complex or highly dynamic.

vpsrini1981 👍 4 Selected: A

Yes, the proposed solution meets the requirements. Publishing events to a custom topic and creating an event subscription for each customer allows for filtering events by event type before processing. This way, each customer's subscription can specify the specific event types they are interested in receiving. Additionally, using Azure Event Grid provides built-in support for authentication and authorization through Microsoft Entra ID, ensuring secure access to the events. Furthermore, by having a separate subscription for each customer, events can be sent to multiple customers while directing them to a single endpoint, thus fulfilling the requirement to push near-real-time information to thousands of customers via a single endpoint.

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Expert Analysis

Why the Answer Is Correct

The proposed solution fails because an Azure Event Grid custom topic supports a maximum of 500 event subscriptions. With thousands of customers, each requiring its own subscription, the design immediately exceeds that hard quota. Although publishing to a single custom topic satisfies the single-endpoint requirement and subscriptions can filter by event type, the per-customer subscription model is not scalable. Event Grid domains are the documented multi-tenant construct that allows up to 100,000 topics and per-customer subscriptions within a domain. Therefore the proposed solution does not meet the goal, making No (B) correct.

Why the Other Options Are Wrong

Choosing Yes (A) overlooks the 500-subscription limit per custom topic. The other requirements — event-type filtering via subscription filters, Microsoft Entra ID authentication/authorization, and a single publishing endpoint — are indeed satisfied, which makes Yes tempting. However, a solution that cannot accommodate the stated scale of thousands of customers does not meet the goal. The question asks whether the solution meets the goal as a whole, and a quota violation is a decisive failure. Community voters who selected Yes generally focused on filtering and authentication while missing the subscription quota.

Community Comment Notes

Several commenters converge on the quota problem: raymond_abcd stated that "The number of subscriptions per custom topic is limited to 500" and linked the official quotas page. egaws noted the 100-custom-topics-per-subscription limit and suggested that "consider using domains, which can support 100,000 topics" when that limit is reached. FeriAZ recommended Event Grid domains so that "Event subscriptions within the domain can then be configured for each customer or customer group," with filtering rules applied per subscriber. vpsrini1981 argued for Yes based on filtering and Entra ID support, but did not address the 500-subscription cap. The majority vote and the comment consensus align with No (B).

Official Reference

Exam Strategy

In Event Grid design questions, always verify subscription and topic quotas before accepting a solution that scales to thousands of tenants. A custom topic's 500-subscription ceiling rules out one-subscription-per-customer, so reach for Event Grid domains when multi-tenancy is required.

Frequently Asked Questions

Why do per-customer event subscriptions fail on an Event Grid custom topic?

A custom topic supports a maximum of 500 event subscriptions, so thousands of customers would exceed that quota.

What is the recommended Event Grid alternative for thousands of customers?

Event Grid domains allow up to 100,000 topics with per-customer subscriptions and filtering, making them the documented multi-tenant pattern.

Related Analysis

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