Function Apps responding with 503 Service Unavailable after a certain number of active instances

Pedro Rodrigues 31 Reputation points


I'm doing a study where I'm collecting data from 100 different Function App instances deployed within the same Region, for the same Resource Group and Subscription.

I've read that the Consumption Plan supports up until 100 Function Apps, however, I noticed during my testing that when I try to trigger 100 functions sequentially (one per function app), at around the app number 60 it responds with a 503 Service Unavailable status code. All the remaining apps respond with the same status code. The first half of the apps I don't encounter any issues.

The function apps are using the exact same source code and were deployed using the ZIP package upload method.

Is there a limitation for the Consumption Plan that I'm missing?

Thanks in advance!

Kind Regards.

Azure Functions
Azure Functions
An Azure service that provides an event-driven serverless compute platform.
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  1. MayankBargali-MSFT 67,001 Reputation points

    @Pexers Thanks for reaching out. Can you please confirm if all your 100 function app is running on the consumption plan? In case if it the same consumption plan then there might be case where there may be high resource utilization at the same second for the same consumption instance which yields to 503 error during that time there the general recommendation is for each function app to have its own Consumption plan.
    Yes, there is limit of 100 consumption plan per region as documented here.

    You can refer to Diagnose and solve problems blade to get more details/insights what would have caused the 503 errors.

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