How to scale up an AppService plan with non-disruptive service

Question

How to scale up an AppService plan with non-disruptive service

Kenji Kagei 5

I would like to scale up the AppService plan that the AppService and function apps are tied to from S2:2 to P0V3:2 with no service interruption.

If I change the AppServiuce plan tied to the production slots to simple, it will result in an application restart and a service outage, right?

Therefore, I have the following response plan.

Proposal 1: Prepare a deployment slot with a different plan for P0V3:2 in advance and switch to the slot of the new plan by slot swapping. (We are concerned that this may cause an application restart.)

Proposal 2: Create a deployment slot with a different plan and the same settings as the production slot and set the traffic % on the [deployment slot] screen to Deployment slot is set to 100 (production slot is 0) while the AppServiuce plan associated with the production slot is scaled up.

What is the best way to do this with no service interruption, including Proposal 1, 2, and other methods?

Alekhya Vaddepally 495 Reputation points Microsoft External Staff

2025-04-09T11:09:13.7133333+00:00
Hi Kenji Kagei,

Make a new app service plan (P0V3: 2)

Make provision of a new app service scheme with the desired level (P0V3: 2).

Clon your existing app service (or function app) to the new app service scheme. To ensure settings, configurations, and deployment slots, you can do this using the azure portal, azure CLI or ARM template.

In this new plan, deploy the latest version of your app, and test it well.

When ready, indicate your DNS or Azure Front Door / Application Gateway on the new app, or if you are using one then switch to traffic using a load balancer or traffic manager.

This approach ensures that, No downtime for existing users during the setup.

When you prepare the new, the existing production environment leads to zero restart.

A smooth transition once the new environment is ready.

If DNS is used for routing, you can use low TTL (Time-to-Live) to make the switchover faster.

https://learn.microsoft.com/en-us/azure/app-service/manage-scale-up
https://learn.microsoft.com/en-us/azure/app-service/deploy-staging-slots?tabs=portal#route-traffic
if you have any further concerns or queries, please feel free to reach out to us.
Kenji Kagei 5 Reputation points

2025-04-09T23:50:49.15+00:00

Thank you for your answer.

As an alternative to a load balancer or traffic manager, is there a problem with the

Proposal 2 to set the deploy slot to 100 (production slot is 0) in the traffic % on the [deploy slot] screen in AppService?

Please tell us what the problem is.

Also, will the application have to be restarted in case of Proposal 1?

Are there any conditions under which an application restart may or may not occur?

If there is no application restart, I would be willing to accept a small blink of an eye and choose the method of proposal 1.
Alekhya Vaddepally 495 Reputation points Microsoft External Staff

2025-04-11T10:53:36.07+00:00

Hi Kenji Kagei,
We haven’t heard from you on the last response and was just checking back to see if you have a resolution yet. In case if you have any resolution, please do share that same with the community as it can be helpful to others. Otherwise, will respond with more details and we will try to help.
Alekhya Vaddepally 495 Reputation points Microsoft External Staff

2025-04-14T07:15:48.0233333+00:00

Hi Kenji Kagei, We haven’t heard from you on the last response and was just checking back to see if you have a resolution yet. In case if you have any resolution, please do share that same with the community as it can be helpful to others. Otherwise, will respond with more details and we will try to help.

1 answer

Your answer

Alekhya Vaddepally 495 Reputation points Microsoft External Staff

2025-04-09T11:09:13.7133333+00:00

Hi Kenji Kagei,

Make a new app service plan (P0V3: 2)

Make provision of a new app service scheme with the desired level (P0V3: 2).

Clon your existing app service (or function app) to the new app service scheme. To ensure settings, configurations, and deployment slots, you can do this using the azure portal, azure CLI or ARM template.

In this new plan, deploy the latest version of your app, and test it well.

When ready, indicate your DNS or Azure Front Door / Application Gateway on the new app, or if you are using one then switch to traffic using a load balancer or traffic manager.

This approach ensures that, No downtime for existing users during the setup.

When you prepare the new, the existing production environment leads to zero restart.

A smooth transition once the new environment is ready.

If DNS is used for routing, you can use low TTL (Time-to-Live) to make the switchover faster.

https://learn.microsoft.com/en-us/azure/app-service/manage-scale-up
https://learn.microsoft.com/en-us/azure/app-service/deploy-staging-slots?tabs=portal#route-traffic
if you have any further concerns or queries, please feel free to reach out to us.
Kenji Kagei 5 Reputation points

2025-04-09T23:50:49.15+00:00

Thank you for your answer.

As an alternative to a load balancer or traffic manager, is there a problem with the

Proposal 2 to set the deploy slot to 100 (production slot is 0) in the traffic % on the [deploy slot] screen in AppService?

Please tell us what the problem is.

Also, will the application have to be restarted in case of Proposal 1?

Are there any conditions under which an application restart may or may not occur?

If there is no application restart, I would be willing to accept a small blink of an eye and choose the method of proposal 1.
Alekhya Vaddepally 495 Reputation points Microsoft External Staff

2025-04-11T10:53:36.07+00:00

Hi Kenji Kagei,
We haven’t heard from you on the last response and was just checking back to see if you have a resolution yet. In case if you have any resolution, please do share that same with the community as it can be helpful to others. Otherwise, will respond with more details and we will try to help.
Alekhya Vaddepally 495 Reputation points Microsoft External Staff

2025-04-14T07:15:48.0233333+00:00

Hi Kenji Kagei, We haven’t heard from you on the last response and was just checking back to see if you have a resolution yet. In case if you have any resolution, please do share that same with the community as it can be helpful to others. Otherwise, will respond with more details and we will try to help.

Answer 1

Hi Kenji Kagei,
Proposal 2:

You asked if setting the deployment slot 100% traffic (with a production slot at 0%) can serve as a workaround to avoid downtime during a scale-up.

While it seems that it can separate production, deployment slots cannot spread to various app service schemes.

So if you are scaling from S2 to P0V3, you cannot assign your deployment slot in a separate app service plan as compared to your production slot.

In other words, both the production slots and all the purposeless slots share the same app service plan. So even if you direct 100% traffic to a slot, the underlying infrastructure is still affected when you scale - and it means:

All slots will restart, in which a traffic is obtained.

Users can experience a brief disruption, even if it is just an eye.

Unfortunately, slot swapping works within only one app service scheme. You cannot swap one slot from one app service plan to another, so the proposal 1 is not viable

Creating a new app service in a separate plan (P0V3),

Posting your app there with the same settings,

And then users root it (perhaps through DNS or similar),

Then it is not really a slot swap, but a blue-green deployment, and it is a valid and recommended zero-downtime strategy.

https://learn.microsoft.com/en-us/azure/app-service/deploy-staging-slots?tabs=portal#how-swapping-works

Yes, when you score an app service plan, the azure will restart all the applications running on it, as the underlying VM SKU and calculation environment change.

This is true, even if you remove the traffic using a deployment slot, as the slots still live under the same plan.

To avoid the restart application, create new azure service plan
if you have any further concerns or queries, please feel free to reach out to us.

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How to scale up an AppService plan with non-disruptive service

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