Azure / Azure/Azure-Spring-Apps

Performance degradation during scale-out operations

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#45 2 comments 0 reactions 1 assignee Claimed by @qingc View on GitHub
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Description

**Describe the bug**
During scale out operations the performace of the application is degraded. It happens with auto-scale and also manual scale. It doesn't happen during scale-in operations.

**To Reproduce**
Steps to reproduce the behavior:
1. Given an application with constant workload.
2. In Azure portal go to apps. Select the application to be scaled-out.
3. Go to scale out settings.
4. Increase the number of instances of the application and save.
5. During the scale-out operation the application throughput is reduced significantly. For instance going from 500K Requests per Second (RPS) to less than 100K RPS. This can be measured using Application Insights.
6. When the scale-out operation completes the throughput recovers and work as expected, increasing accordingly to new number of instances.

**Expected behavior**
The expected behavior is that the performance of the application stays stable during the scale-out operation. Once the operation is complete, then throughput should improve.
That is specially important for systems under heavy load. If there is auto-scale in place usally is triggered when more performance is needed, but during this scale-out operation process the performance of the solution goes down.

**Screenshots**
![image](https://user-images.githubusercontent.com/52053185/235327318-8a1f75ce-3b3c-4701-87da-5a9ba29e49ae.png)

**Additional context**
To generate the load I was using Azure Load Testing and the load was constant, that is why it is possible to detect this situation.

**Can we contact you for additional details?** Y/N

If yes, please send us your contact information to AzureSpringCloud-Talk@service.microsoft.com and include the issue number in the email title.

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