CODEWITHSUNDEEP
azureazure-web-app-service
wallismark
wallismark

Reputation: 1856

Exclude an Azure AppService instance from load balancing

Is there a way to exclude an AppService instance from the Load Balancer:

  1. Via the portal?
  2. Via the SDK?

Via the SDK would be ideal, then we could set the MakeVisibleToLoadBalance flag (if such a thing existed) once all initialization completed.

If it's only available via the portal, it would be good to set n seconds after an instance is loaded before it becomes visible to the load balancer.

Reason: When we restart an instance (e.g. via advanced restart), the metrics show a significant increase in response times, every time. I believe the cause is the load balancer thinks the machine is available but it really hasn't completed initialization, so requests that the load balancer sends to that instance are significantly delayed.

Another reason is we may observe an instance is performing poorly, it would be great if we could exclude that instance until either it recovered or was restarted.

Upvotes: 1

Views: 646

Answers (2)

AjayKumar
AjayKumar

Reputation: 3173

//As per the discussion with wallismark in the 'comments'. Copied the helpful comments to answer.

To fix the 'reason'/scenarios you have mentioned above, you could leverage ApplicationInitialization method. Every time your application starts, this can be because of a new worker coming online (horizontal scaling) or even just a cold start caused by a new deployment, config change etc. The ApplicationInitialization will be executed to warm up the site before accepting requests on that worker.

So the Application Initialization Module, handy feature that allows you to warm your app prior to the application receiving requests to help avoid the cold-start or slow initial load times when the app is restarted. Please checkout - https://ruslany.net/2015/09/how-to-warm-up-azure-web-app-during-deployment-slots-swap/ - It has also been implemented for all other operations in which a new worker is provisioned (such as auto scale, manual scale or Azure fabric maintenance). But, you cannot exclude the instance from the load balancer.

Upvotes: 1

AjayKumar
AjayKumar

Reputation: 3173

If your requirement fits, you could leverage ARR affinity; in a multi-instance deployment, ensures that the client is routed to the same instance for the life of the session. You can set this option to Off for stateless applications.

Typically, the Scale-out (trigger) -multiple running copies of your WebApps and handle the load balancing configurations necessary to distribute incoming requests across all instances. When you have more than one instance a request made to your WebApp can go to any of them using a load-balancer that will decide which instance to route the request based on how busy each instance is at the time.

To share more information on this feature - On load-balancer is that once a request from your browser is made to the site, it will add a ARRAffinity cookie to it (with the response) containing the specific instance id that will make the next request from this browser go to the same instance. You can use this feature to send a request to a specific instance of our site. You can find the setting in the App Service's Application Settings: When multiple apps are run in the same App Service plan, each scaled-out instance runs all the apps in the plan.

Upvotes: 0

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