Azure function: limit the number of calls per second

Question

I have an Azure function triggered by queue messages. This function makes a request to third-party API. Unfortunately this API has limit - 10 transactions per second, but I might have more than 10 messages per second in service bus queue. How can I limit the number of calls of Azure function to satisfy third-party API limitations?

Answer 1

Unfortunately there is no built-in option for this.

The only reliable way to limit concurrent executions would be to run on a fixed App Service Plan (not Consumption Plan) with just 1 instance running all the time. You will have to pay for this instance.

Then set the option in host.json file:

"serviceBus": {
    // The maximum number of concurrent calls to the callback the message
    // pump should initiate. The default is 16.
    "maxConcurrentCalls": 10
}

Finally, make sure your function takes a second to execute (or other minimal duration, and adjust concurrent calls accordingly).

As @SeanFeldman suggested, see some other ideas in this answer. It's about Storage Queues, but applies to Service Bus too.