The AEG provides durable delivery for each event message at least once to each subscriber based on its subscription. More details can be found in the docs.
In the case, when the AEG can not successfully deliver a message after retrying, the dead-lettering feature (configured for each subscriber) can be used for notification and/or analyzing process via a storage eventing, where a dead-letter message is stored.
On the publisher side, the publisher received a standard Http response from the event domain endpoint immediately after its posting, see more details in the docs.
The current version of the AEG is not integrated to the Diagnostic settings (for instance, like it is done for Event Hubs) which will be enabled to push the metrics and/or logs to the stream pipeline for their analyzing process.
However, as a workaround for that, the Azure Monitoring REST API can help you.
Using Lists the metrics values for event domain, we can obtained the metrics for topics such as Publish Succeeded, Publish Failed and Unmatched.
the following is an example of the REST Get:
https://management.azure.com/subscriptions/{myId}/resourceGroups/{myRG}/providers/Microsoft.EventGrid/domains/{myDomain}/providers/Microsoft.Insights/metrics?api-version=2018-01-01&interval=PT1M&aggregation=none&metricnames=PublishSuccessCount,PublishFailCount,PublishSuccessLatencyInMs,DroppedEventCount
Based on the polling technique, you can push the event domain metrics values to the stream pipeline for their analyzing, monitoring, alerting, etc. using an Azure Stream Analytics job. Your management requirements (for instance, publisher_topic1 is disabled, etc.) can be referenced to the input stream job.
Note, that the event domain metrics didn't give a topic granularity and also there is no an activity event log at that level. I do recommend to use the AEG feedback page.
