Integration Event routing

Event Grid custom topic

Event Grid custom topic is a user-created Azure Event Grid topic that gives custom applications an endpoint for publishing business or application events. In Azure, it shows up when custom applications publish shipment, order, payment, device, or workflow events that subscribers need to process independently. Teams use it to review topic name, region, access keys or managed identity options, input schema, event subscriptions, filters, retry policy, dead-letter destination, and monitoring before changing production behavior. It is not an Azure system topic, Event Grid domain, Event Hub, or Service Bus topic.

Source: Microsoft Learn - Custom topics in Azure Event Grid Reviewed 2026-05-14

Exam trap: Treating Event Grid custom topic as a diagram label instead of checking the exact source resource ID, handler, identity, and event subscription.
Production check: Verify source resource ID, subscription name, destination type, delivery schema, filters, retry policy, and dead-letter settings.

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Article details and learning context

Aliases: Azure Event Grid custom topic, custom Event Grid topic
Difficulty: intermediate
CLI mappings: 5
Last verified: 2026-05-14

Related context No curated learning path mapped yet; use the category trail.

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Understand the concept

Why it matters

Event Grid custom topic matters because Event Grid workflows fail in ways that are easy to misread: a publisher can succeed while a handler never receives the event, a filter can exclude the right payload, or an identity change can turn delivery into repeated failures. Clear vocabulary keeps architects, developers, operators, security reviewers, and business owners aligned on the exact routing behavior. It also improves change review because teams can ask who owns the setting, which events are affected, which handler depends on it, and what evidence proves the current state before a release, incident, audit, or cost review. This keeps ownership, evidence, change control, and customer impact visible before the next production decision.

Official wording and source

Event Grid custom topic is a user-created Azure Event Grid topic that gives custom applications an endpoint for publishing business or application events. Microsoft Learn places it in Custom topics in Azure Event Grid; operators confirm scope, configuration, dependencies, and production impact.

Open Microsoft Learn

Technical context

Technically, Event Grid custom topic sits inside the Azure Event Grid control plane and runtime delivery path. The main moving parts are topic endpoint, access keys, publisher application, event schema, event subscriptions, filters, handlers, delivery retry, dead-letter storage, and Azure Monitor metrics. It is usually created or inspected through the Azure portal, ARM or Bicep, REST, and Azure CLI. Production teams should connect the configured resource ID, schema choice, endpoint behavior, identity, logs, and metrics so troubleshooting can move from an architecture diagram to verifiable Azure evidence.

Exam context

Compare with

Event Grid domain Event Grid system topic Event Hub Service Bus topic Storage queue

Where it is used

Where you see it

Event Grid Topics portal blade, topic endpoint, access keys, input schema, system-assigned identity settings, and topic metrics show whether a custom publisher has a governed event entry point.
Application code, IaC templates, and deployment parameters reveal topic names, regions, schema choices, access settings, and event subscriptions that connect publishers to independent handlers during production review.
Azure Monitor metrics, delivery failures, Activity Log writes, and dead-letter storage prove whether published custom events are matched, delivered, retried, or dropped after production changes.

Common situations

Publish custom application events from a line-of-business system.
Confirm which handlers subscribe to a custom event source.
Check topic health, endpoint settings, and delivery metrics before release.

Illustrative Azure scenarios

These examples show how the concept can affect design and operations. They are illustrative scenarios, not customer claims.

Scenario 01 Event Grid custom topic in action for logistics Scenario, objectives, solution, measured impact, and takeaway.

Scenario

Northline Freight, a logistics organization, needed to solve a concrete production challenge: shipment status applications needed to notify customer portals, warehouse screens, and billing services without point-to-point integrations. The platform team focused on Event Grid custom topic so the event-driven workflow could be changed with measurable evidence instead of guesswork.

Goals

Reduce custom integration changes by 60 percent
Deliver milestone events within five seconds
Add new subscribers without publisher code changes
Expose failed deliveries to support

Approach using Event Grid custom topic

Architects configured a custom topic as the governed publishing endpoint for application events. They tied the design to Event Grid topics or domains, event subscriptions, filters, delivery schema, destination handlers, Azure Monitor metrics, and approved runbooks. The implementation recorded the source resource ID, responsible owner, expected event types, sample payloads, identity or key choice, retry behavior, dead-letter plan, and rollback steps. Engineers first captured read-only CLI output and portal evidence, then deployed the approved configuration through infrastructure as code. During validation, the team tested successful delivery, endpoint failure, authorization failure, and payload mismatch so operators knew exactly which signal to check before making production changes.

Potential outcomes

Shipment integrations dropped from twelve direct calls to one topic route.
Median event delivery was 2.8 seconds during peak scans.
A returns handler was added in one sprint without changing the publisher.
Support used metrics and dead-letter storage to resolve three carrier endpoint failures.

What to learn

Event Grid custom topic is valuable when teams connect event-routing design to live Azure configuration, observable evidence, and an accountable operating model.

Scenario 02 Event Grid custom topic in action for healthcare claims Scenario, objectives, solution, measured impact, and takeaway.

Scenario

HarborStone Health, a healthcare claims organization, needed to solve a concrete production challenge: claims adjudication events had to notify case management, document indexing, and member messaging while preserving audit evidence. The platform team focused on Event Grid custom topic so the event-driven workflow could be changed with measurable evidence instead of guesswork.

Goals

Separate claim publishers from downstream services
Keep regulated event data on approved handlers
Detect delivery failures within fifteen minutes
Support independent handler releases

Approach using Event Grid custom topic

The team designed the solution around custom topic as an explicit production control, not just a diagram term. They mapped publisher responsibilities, subscription settings, handler ownership, filters, schema expectations, retry handling, dead-letter storage, and security permissions. Azure Monitor dashboards tracked published, matched, delivered, failed, and dead-lettered events. The change package included sample events, CLI evidence, access review notes, and an incident procedure. Mutating commands were blocked without approval, while read-only commands became the first step for support engineers validating whether Event Grid, the handler, or a downstream dependency caused the issue.

Potential outcomes

Claim event fan-out no longer required publisher redeployment.
Security reviewers approved scoped access and monitored delivery evidence.
Failure alerts fired within nine minutes during testing.
Handler release windows became independent and reduced change conflicts by 40 percent.

What to learn

Event Grid custom topic is valuable when teams connect event-routing design to live Azure configuration, observable evidence, and an accountable operating model.

Scenario 03 Event Grid custom topic in action for manufacturing Scenario, objectives, solution, measured impact, and takeaway.

Scenario

Fabrikam Robotics, a manufacturing organization, needed to solve a concrete production challenge: factory applications needed a shared event entry point for quality alerts, work-order updates, and maintenance notifications. The platform team focused on Event Grid custom topic so the event-driven workflow could be changed with measurable evidence instead of guesswork.

Goals

Route plant events to multiple operational systems
Keep event ownership visible by line and application
Avoid polling for quality exceptions
Measure publish and delivery health daily

Approach using Event Grid custom topic

Engineers implemented Event Grid custom topic with a small reference architecture before rolling it into production. The reference included a source event, configured subscription, approved handler, test payload, monitored metric, and documented failure path. Security reviewed identity and payload access. Operations reviewed alert thresholds, dead-letter handling, and replay ownership. Developers updated handler tests to match the selected event schema and filter behavior. After deployment, daily checks compared expected event volume with matched and delivered counts so the team could catch drift before customers noticed missing or delayed automation.

Potential outcomes

Polling jobs were retired for three production lines.
Quality alert latency fell from fifteen minutes to under one minute.
Each subscription had a named owner and dashboard.
Maintenance teams added a handler without MES code changes.

What to learn

Event Grid custom topic is valuable when teams connect event-routing design to live Azure configuration, observable evidence, and an accountable operating model.

Azure CLI

Azure CLI is useful for Event Grid custom topic because it gives operators reproducible evidence for the source, subscription, handler, schema, filter, retry, identity, and metrics before any mutating change is approved.

Useful for

Publish custom application events from a line-of-business system.
Confirm which handlers subscribe to a custom event source.
Check topic health, endpoint settings, and delivery metrics before release.

Before you run a command

Confirm the tenant, subscription, resource group, source resource ID, handler, and environment are the intended production or nonproduction scope.
Capture read-only evidence first, including current event subscriptions, filters, schema, retry, dead-letter, identity, and recent delivery metrics.
Get approval before create, update, delete, key, identity, role assignment, or endpoint changes because those actions can reroute or stop events.

What the output tells you

Resource IDs, endpoints, schemas, filters, identities, and retry settings show what Event Grid is configured to do right now.
Metrics and logs show whether events are being published, matched, delivered, failed, retried, or dead-lettered after recent changes.
Role assignment and identity output shows whether delivery failures are likely authorization problems rather than application defects.

Mapped commands

Event Grid operational checks

direct

az eventgrid topic list --resource-group <resource-group> --output table

az eventgrid topicdiscoverIntegration

az eventgrid topic show --name <topic-name> --resource-group <resource-group>

az eventgrid topicdiscoverIntegration

az eventgrid topic create --name <topic-name> --resource-group <resource-group> --location <region>

az eventgrid topicprovisionIntegration

az eventgrid event-subscription list --source-resource-id <topic-resource-id> --output table

az eventgrid event-subscriptiondiscoverIntegration

az monitor metrics list --resource <topic-resource-id> --interval PT1H

az monitor metricsdiscoverIntegration

Architecture context

Event Grid custom topic belongs in the Event Grid routing architecture with explicit publishers, subscriptions, handlers, filters, schemas, retry policy, dead-lettering, identity, monitoring, and rollback ownership.

Security: Security for Event Grid custom topic starts with knowing which identity, key, role assignment, endpoint, or storage resource can publish, configure, receive, or recover events. Avoid anonymous delivery paths where a managed identity, Microsoft Entra protected endpoint, or least-privilege Azure RBAC role is appropriate. Protect event payloads because metadata and data fields can expose tenant IDs, object names, user activity, or business workflow details. Review Activity Log changes, role assignments, private endpoint requirements, and diagnostic settings before production updates. For regulated data, document who can view dead-letter payloads and who may replay or reprocess them. This keeps ownership, evidence, change control, and customer impact visible before the next production decision.
Cost: Cost for Event Grid custom topic usually comes from event operations, handler executions, downstream queue or stream processing, storage for dead-letter payloads, logging, alerting, and repeated retry activity. A small event route can become expensive when noisy publishers, broad filters, duplicate subscriptions, or failing handlers multiply delivery attempts. Review expected event rate, matched event count, failed delivery count, log retention, and downstream execution cost together. Use tags, budgets, and ownership labels so cost analysis can distinguish planned integration volume from accidental fan-out or retry storms. Retire unused subscriptions and test topics before they become permanent background spend. This keeps ownership, evidence, change control, and customer impact visible before the next production decision.
Reliability: Reliability for Event Grid custom topic depends on accurate source routing, compatible event schema, healthy handlers, retry behavior, dead-letter handling, and clear monitoring. Event Grid can accept an event while downstream processing still fails, so success must be measured across publish, match, delivery, and handler processing stages. Test endpoint outage, authorization failure, malformed payload, noisy publisher, and filter drift scenarios before relying on the workflow. Keep replay and cleanup procedures documented. During incidents, compare recent Activity Log entries, handler logs, Event Grid metrics, and dead-letter contents before changing routing or retry settings. This keeps ownership, evidence, change control, and customer impact visible before the next production decision.
Performance: Performance for Event Grid custom topic is about how quickly relevant events move from publisher to handler without creating avoidable fan-out, parsing, or retry delay. Broad filters, slow endpoints, oversized payloads, schema mismatches, cold-starting functions, or throttled downstream services can turn near-real-time routing into delayed processing. Measure publish latency, matched event rate, delivery success, handler duration, and retry patterns together. Design handlers to acknowledge events quickly, offload long work where needed, and scale independently. Use Event Hubs, Service Bus, or queues when buffering is more important than immediate handler execution. This keeps ownership, evidence, change control, and customer impact visible before the next production decision.
Operations: Operations for Event Grid custom topic should be runbook-driven. The runbook needs the resource ID, owner, environment, publisher, handler, schema, filter, retry policy, dead-letter location, dashboards, and first read-only CLI commands. Operators should know which metric proves publish volume, which metric proves matching, and which log proves delivery failure. Change tickets should include expected event types, sample payloads, rollback instructions, and who can approve mutating commands. When support receives an alert, the first task is to locate the exact subscription or topic, not to restart every dependent service. This keeps ownership, evidence, change control, and customer impact visible before the next production decision.

Common mistakes

Treating Event Grid custom topic as a diagram label instead of checking the exact source resource ID, handler, identity, and event subscription.
Changing filters, retry, schema, or destination settings before saving read-only evidence and confirming the approved rollback path.
Assuming publisher success means end-to-end success even when the handler is failing, throttled, unauthorized, or receiving the wrong schema.