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If app service plan has multiple instances and one of the instance crashes for some reason. the other instances will continue to run without impacting app?

Avinash patil
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  • If you mean web app and its slots. Yes, of course. – Joy Wang Sep 19 '18 at 08:27
  • @JoyWang - Suppose ASP is scaled to 3 instances and it has single web app in it. if one of the instance from ASP is crashed then, is the web app still work without any impact? – Avinash patil Sep 19 '18 at 08:31
  • Yes, they will not affect each other. – Joy Wang Sep 19 '18 at 08:36
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    Refer to this [post](https://stackoverflow.com/questions/12361941/azure-instances-and-web-role),as mentioned in the answer, `If you have an application deployed with 2 instances, even if 1 instance goes down, your 2nd instance will be able to serve your clients` – Joy Wang Sep 19 '18 at 08:48
  • The post https://stackoverflow.com/questions/12361941/azure-instances-and-web-role you sent is for cloud service, where i am looking for App service. – Avinash patil Sep 19 '18 at 08:52
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    The app service instance is also VM, refer to this [doc](https://learn.microsoft.com/en-us/Azure/app-service/web-sites-scale), `Scale out:Increase the number of VM instances that run your app.` – Joy Wang Sep 19 '18 at 08:54

1 Answers1

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If you have an application deployed with 2 instances, even if 1 instance goes down, your 2nd instance will be able to serve your clients

Assuming that you create a website (a windows server with IIS), then your website would has the App Pool which defines the available resources for your website. Each instance could handle a limited number of requests, in order to reduce the response time, you could scale out your website into multiple instances, then each web-server could split the work load

When you scale out you create more PaaS instances of the VM's hosting your App, so when you scale out you are not getting another App Pool in the same IIS, you are getting another App Pool on the other IIS on the other VM. To clarify the comment, the App Service Plan is a collection of Windows VM's with IIS installed on them. All the Apps assigned to that App Service Plan are hosted on ALL the instances of those VM's

the scale out would create multiple copies of your web app and add a Load Balance to distribute the requests between them automatically. And you don't need to configure the load balance separately by yourself.

The home directory contains an app's content, and application code can write to it. If an app runs on multiple instances, the home directory is shared among all instances so that all instances see the same directory. So, if an app saves uploaded files to the home directory, those files are immediately available to all instances.

Refer below links for more details :

  1. Azure instances and web role
  2. https://learn.microsoft.com/en-us/Azure/app-service/web-sites-scale
Avinash patil
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