Is there a limit on simultaneous clients for Event Grid? We can consistently run about 500 simultaneously, but after 700 the connects get rejected. A reference URL to the limit would be appreciated.

Hi, From your description I'm unsure which limit you are hitting. Each topic can have a maximum of 500 subscribers, perhaps that is what you are seeing? You mentioned 500, but then you mentioned 700, so I was unsure if you are having success between 500 and 700. What response status code and error description are you receiving from the REST API when connection is rejected? How many throughput units (TUs) do you have? Please review article below for Event Grid limitations: Event Grid limits https://learn.microsoft.com/en-us/azure/azure-resource-manager/management/azure-subscription-service-limits#event-grid-limits Please click Accept Answer if the above was useful. Thanks. -TP

Azure Event limit on clients

Accepted answer

TP 83,971 Reputation points

2023-07-17T17:17:17.9333333+00:00

Hi,

From your description I'm unsure which limit you are hitting. Each topic can have a maximum of 500 subscribers, perhaps that is what you are seeing? You mentioned 500, but then you mentioned 700, so I was unsure if you are having success between 500 and 700.

What response status code and error description are you receiving from the REST API when connection is rejected?

How many throughput units (TUs) do you have?

Please review article below for Event Grid limitations:

Event Grid limits

https://learn.microsoft.com/en-us/azure/azure-resource-manager/management/azure-subscription-service-limits#event-grid-limits

Please click Accept Answer if the above was useful.

Thanks.

-TP
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Uwe Zimmermann 30 Reputation points

2023-07-17T17:38:39.7766667+00:00

This is many MQTT PUBLISHER clients to a single topic namespace (but unique topics).

Small set of subscribers (1 or 2).

Here is a video of 500 successful

https://www.youtube.com/watch?v=S7Zh-rBlfPQ

After about 700, furter socket connects time out even after waiting 50 seconds.

We seem to be way below "10,000 clients per TU".

Still guessing, because there is a circular reference between

https://learn.microsoft.com/en-us/azure/event-grid/concepts-pull-delivery#throughput-units

and

https://learn.microsoft.com/en-us/azure/event-grid/quotas-limits

TP 83,971 Reputation points

2023-07-17T18:28:05.1133333+00:00

@Uwe Zimmermann So far nothing (in documented limits) is standing out to me as the issue either. Have you looked at all the Event Grid metrics to see if any indicate a problem when you see the socket timeouts? Just for testing you may want to bump up TUs, run test again and see if it changes number you can reach in any significant way. This way at least you would know it is capacity related.

Uwe Zimmermann 30 Reputation points

2023-07-17T18:44:40.01+00:00

I have doubled the TUs from 1 to 2, and no change in behavior.

I now consistently can make it fail:

get to 500 clients publishing at combined 50 msgs / sec

start 2 more, it works

cannot start any more, no matter what I try

UPDATE: neither does 4 TUs

UPDATE: the problem has been solved. 1000 clients work.
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Azure Event limit on clients

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