How to stop container app from scaling down after cooldown period?

Question

How to stop container app from scaling down after cooldown period?

Filipp Trigub 0

Hi there,

I got an app, which is scaled to 0. WHen I give it a task, this task might need to run for a while. How can I stop the app from scaling down to 0, if the task is not finished?

Best,

Filipp

Khadeer Ali 5,990 Reputation points Microsoft External Staff Moderator

2025-04-11T16:11:18.6233333+00:00

@Filipp Trigub ,

Thanks for reaching out. To prevent your container app from scaling down to zero while a long-running task is in progress, you can consider a couple of approaches.

One way is to proactively wake the app before it's needed — for example, using a scheduled trigger or warm-up request just before the task starts. This helps ensure the app stays active and doesn’t scale down right when work is about to begin. Microsoft's docs on scaling explain this behavior in detail.

Another important point: Azure Container Apps only scale down when there's no activity. So if the task runs inside an active request or event trigger, the container won't scale down until it's done. But if you're triggering the task asynchronously and the app becomes idle, it can still scale down. In such cases, increasing the cooldownPeriod or keeping minReplicas to at least 1 can help.

Also, while health probes (like liveness and readiness) are useful for stability, they don’t affect scaling directly. They're more about startup timing and making sure your app is healthy enough to receive traffic (ref).
Filipp Trigub 0 Reputation points

2025-04-11T16:34:39.26+00:00

Hi Khadeer,

thank you first of all!
Would you tell me: how can I run a task inside an active request? Does that simply mean that I should not run the task in a background process (thread of async loop)?

My current approach is to constantly ping the app. Crude, but seems to do the trick....
Praveen Kumar Gudipudi 1,805 Reputation points Microsoft External Staff Moderator

2025-04-11T20:05:05.8066667+00:00

Hello @Filipp Trigub ,

Yes — you're spot on. Running a task "inside an active request" means the task should be part of the actual request-response cycle. So ideally, you would not offload it to a background thread or fire-and-forget async task. Instead, the request should stay open and wait until the task completes before sending a response back to the client.Here’s why: Azure Container Apps look at whether there’s any active load (like an ongoing HTTP request or message). If the app quickly returns a response and then continues processing in the background, the platform may think it’s idle and start scaling it down — even if work is still happening behind the scenes.

If you’re using async/await properly and the task is awaited as part of the request, you’re good. But if you’re using something like Task.Run(...) or background timers that disconnect from the original request, that would be considered "out-of-band" and may not keep the container alive.

So yes — keeping the task tied directly to the request (and keeping the request open) is the best way to prevent scale-down in that scenario.
Filipp Trigub 0 Reputation points

2025-04-14T09:13:51.8233333+00:00

Ok, I see. The tasks are running for several hours though, so keeping a request open for such a long time is not a good practice.

Would be nice to have more control over the scaling down of apps, maybe via a specified endpoint.
Khadeer Ali 5,990 Reputation points Microsoft External Staff Moderator

2025-04-14T12:54:39.5466667+00:00

Keeping a request open for several hours isn’t really practical, and you're right, it would be nice if we had more fine-grained control over when the app scales down — like via a dedicated endpoint or some kind of “do not scale down” flag.

At the moment, one workaround I’ve seen work reasonably well is setting the minReplicas to 1 during long-running task windows. That way, the app won’t scale down to 0 and kill the process mid-way. Not the cleanest solution, but it’s reliable when tasks run for extended periods.
Khadeer Ali 5,990 Reputation points Microsoft External Staff Moderator

2025-04-15T10:00:51.9633333+00:00

@Filipp Trigub ,

Just following up again to see if there's anything else I can assist you with.
Khadeer Ali 5,990 Reputation points Microsoft External Staff Moderator

2025-04-16T14:59:29.2533333+00:00

@Filipp Trigub ,

Just following up to see if you were able to resolve the issue or if there's anything else I can assist you with.

Your answer

Khadeer Ali 5,990 Reputation points Microsoft External Staff Moderator

2025-04-11T16:11:18.6233333+00:00

@Filipp Trigub ,

Thanks for reaching out. To prevent your container app from scaling down to zero while a long-running task is in progress, you can consider a couple of approaches.

One way is to proactively wake the app before it's needed — for example, using a scheduled trigger or warm-up request just before the task starts. This helps ensure the app stays active and doesn’t scale down right when work is about to begin. Microsoft's docs on scaling explain this behavior in detail.

Another important point: Azure Container Apps only scale down when there's no activity. So if the task runs inside an active request or event trigger, the container won't scale down until it's done. But if you're triggering the task asynchronously and the app becomes idle, it can still scale down. In such cases, increasing the cooldownPeriod or keeping minReplicas to at least 1 can help.

Also, while health probes (like liveness and readiness) are useful for stability, they don’t affect scaling directly. They're more about startup timing and making sure your app is healthy enough to receive traffic (ref).
Filipp Trigub 0 Reputation points

2025-04-11T16:34:39.26+00:00

Hi Khadeer,

thank you first of all!
Would you tell me: how can I run a task inside an active request? Does that simply mean that I should not run the task in a background process (thread of async loop)?

My current approach is to constantly ping the app. Crude, but seems to do the trick....
Praveen Kumar Gudipudi 1,805 Reputation points Microsoft External Staff Moderator

2025-04-11T20:05:05.8066667+00:00

Hello @Filipp Trigub ,

Yes — you're spot on. Running a task "inside an active request" means the task should be part of the actual request-response cycle. So ideally, you would not offload it to a background thread or fire-and-forget async task. Instead, the request should stay open and wait until the task completes before sending a response back to the client.Here’s why: Azure Container Apps look at whether there’s any active load (like an ongoing HTTP request or message). If the app quickly returns a response and then continues processing in the background, the platform may think it’s idle and start scaling it down — even if work is still happening behind the scenes.

If you’re using async/await properly and the task is awaited as part of the request, you’re good. But if you’re using something like Task.Run(...) or background timers that disconnect from the original request, that would be considered "out-of-band" and may not keep the container alive.

So yes — keeping the task tied directly to the request (and keeping the request open) is the best way to prevent scale-down in that scenario.
Filipp Trigub 0 Reputation points

2025-04-14T09:13:51.8233333+00:00

Ok, I see. The tasks are running for several hours though, so keeping a request open for such a long time is not a good practice.

Would be nice to have more control over the scaling down of apps, maybe via a specified endpoint.
Khadeer Ali 5,990 Reputation points Microsoft External Staff Moderator

2025-04-14T12:54:39.5466667+00:00

Keeping a request open for several hours isn’t really practical, and you're right, it would be nice if we had more fine-grained control over when the app scales down — like via a dedicated endpoint or some kind of “do not scale down” flag.

At the moment, one workaround I’ve seen work reasonably well is setting the minReplicas to 1 during long-running task windows. That way, the app won’t scale down to 0 and kill the process mid-way. Not the cleanest solution, but it’s reliable when tasks run for extended periods.
Khadeer Ali 5,990 Reputation points Microsoft External Staff Moderator

2025-04-15T10:00:51.9633333+00:00

@Filipp Trigub ,

Just following up again to see if there's anything else I can assist you with.
Khadeer Ali 5,990 Reputation points Microsoft External Staff Moderator

2025-04-16T14:59:29.2533333+00:00

@Filipp Trigub ,

Just following up to see if you were able to resolve the issue or if there's anything else I can assist you with.

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How to stop container app from scaling down after cooldown period?

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