Not enough available reserved instance servers to satisfy this request.

Bäcker 21 Reputation points
2020-05-18T09:21:28.51+00:00

Hi. Three hours before bigger events we scale-out a SignalR “App Services” application. The 17:th of May however we got this issue:

“Not enough available reserved instance servers to satisfy this request. Currently 18 instances are available. If you are changing instance size you can reserve up to 18 instances at this moment. If you are increasing instance count then you can add extra 18 instances at this moment. Please get available machines and retry later.”

Sadly, we didn’t get the resources needed to the event and it got a big impact on end consumer experience.

Question:
How can we be sure to get the resources needed? We are using scale-out to keep costs down, only needing 1 instance as default (events are one day a week). If the cluster is busy, how long time does it take to add more power? Would it help to scale-out more than 3 hours in advance (and what would that timeframe be)?

Azure App Service
Azure App Service
Azure App Service is a service used to create and deploy scalable, mission-critical web apps.
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  1. brtrach-MSFT 15,791 Reputation points Microsoft Employee
    2020-07-24T21:00:00.867+00:00

    Yes, there is logic that resizes instances within Azure Web Apps every couple of hours based on need. Since this sounds business critical, I would suggest scaling at least 6 hours before. In the above error message, you should have been able to ingest at least 18 additional instances. You should always take whatever is available at the time so the internal logic will add more instances when it runs again.

    The best practice for large scaling in the cloud is to give yourself enough time. You may find that you need even more than 6 hours if you're doing very large scaling. Basically, the more instances you plan on needing, the earlier you should start your scaling requests.

    The above is best practices for short term. Long term, you should look into using Azure Traffic Manager (ATM) and setting up your web app in multiple regions. This way, if a region is getting hit hard, you can scale your apps out in other regions that will likely have better availability. ATM will also allow you to place instances closer to each customer for better overall performance as well.

    Please let us know if there are any other questions we can assist you with.

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