About Uniform and Flexible Mode Instances in Azure Scale Sets I want to know the difference.

浩明島田 20

Uniform mode and flexible mode instances can be handled in the same way as normal VMs in flexible mode, but the uniform mode is treated as an instance within a scale set and the specifications are different from normal VMs. Availability of JIT function of Microsoft Defender for Cloud, availability of az ssh command

I would like to check the uniform mode and flexible mode for each.

浩明島田 20 Reputation points

2023-03-06T06:39:19.56+00:00

Thank you for your reply.

Please ask the following additional questions.

・How to set the uniform mode JIT function

・The reason why the JIT function cannot be used in flexible mode (because it should be available as a normal VM, and it is also displayed in the list of VMs that apply the JIT function in Microsoft Defender for Servers. Please answer if possible.)

・Whether it is possible to SSH into a uniform mode or flexible mode instance using Azure CLI.

・Is it possible to collect logs of scaled-out instances in uniform mode and flexible mode respectively?

・What is the reason for limited functionality in uniform mode instances?
vipullag-MSFT 24,441 Reputation points

2023-03-07T04:54:15.82+00:00

Hello 浩明島田

Please find responses:

・How to set the uniform mode JIT function

To set the JIT function in uniform mode, you need to enable the "Just-In-Time access" feature in the Azure Security Center. Once enabled, you can configure JIT policies for your scale set instances, which allows you to control the time window and the scope of the access for your VMs.

・The reason why the JIT function cannot be used in flexible mode (because it should be available as a normal VM, and it is also displayed in the list of VMs that apply the JIT function in Microsoft Defender for Servers. Please answer if possible.)

The JIT function is not available in flexible mode because each VM instance in a flexible mode scale set can have different sizes, configurations, and workloads. This makes it difficult to apply a consistent JIT policy to all VM instances in the scale set.

・Whether it is possible to SSH into a uniform mode or flexible mode instance using Azure CLI.

Yes, it is possible to SSH into a uniform mode or flexible mode instance using Azure CLI.

・Is it possible to collect logs of scaled-out instances in uniform mode and flexible mode respectively?

Yes, it is possible to collect logs of scaled-out instances in both uniform mode and flexible mode. In uniform mode, you can use the Azure Log Analytics workspace to collect and analyze logs from all VM instances in the scale set. In flexible mode, you can use the Azure Monitor agent to collect and send logs from each VM instance to a central log storage, such as Azure Blob storage or Azure Log Analytics workspace.

・What is the reason for limited functionality in uniform mode instances?

Due to their specialized nature as a part of a scale set. Uniform mode instances are designed to work as a group of identical VMs that can handle the same workload, which makes it easier to manage and scale them as a single unit.

Hope this helps.

3 answers

vipullag-MSFT 24,441 Reputation points

2023-03-07T04:54:26.2433333+00:00

Hello,

Welcome to Microsoft Q&A Platform, thanks for posting your query here.

The Flexible orchestration mode provides a unified experience across the Azure VM ecosystem. Flexible orchestration offers high availability guarantees (up to 1000 VMs) by spreading VMs across fault domains in a region or within an Availability Zone. This enables you to scale out your application while maintaining fault domain isolation that is essential to run quorum-based or stateful workloads. Flexible orchestration mode can be used with all VM sizes and provides the highest scale and configurability for VM sizes that support memory preserving updates or live migration.

Uniform mode instances are identical VMs that are created from the same image and have the same configuration settings. In uniform mode, all VM instances in the scale set have the same size, disk settings, and other configuration settings. This mode is useful when you need a group of identical VMs that can handle the same workload.

Both uniform and flexible mode instances can be managed in the same way as normal VMs, including using Azure Management Portal, Azure CLI, PowerShell, and other Azure management tools. However, there are some differences in terms of how you can configure and manage them. For example, some features may only be available for one mode or the other.

The Just-in-Time (JIT) function of Microsoft Defender for Cloud, you cannot set JIT on uniform VMSS but you can set JIT on Flex, while the availability of the "az ssh" command may vary depending on the mode and the specific VM configuration.

Hope this helps.
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1 person found this answer helpful.
浩明島田 20 Reputation points

2023-03-07T10:25:07.05+00:00

Please confirm additionally.

Could you tell me about the detailed setting method for using the JIT function for each scale set in uniform mode? Normally, when enabling the JIT function in a VM, it can be set from the "Configuration" tab, but for uniform mode instances, the "Configuration" tab cannot be checked and cannot be set. I would like to know how to set it up for each scale set instead of individual VMs.

Regarding the flexible mode, is it correct to understand that the JIT function can be used for individual VMs, although it cannot be used for each scale set? When I verified it in my environment, I was able to set it for each VM, so I confirmed it.

Although it is a duplicate of the above, please tell me whether the JIT function can be used for each scale set and each VM for uniform mode and flexible mode. Thank you.

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浩明島田 20 Reputation points

2023-03-07T10:45:25.1+00:00

excuse me. As shown in the image below, the scale set is not displayed in the first place.

vipullag-MSFT 24,441 Reputation points

2023-03-07T11:07:10.8933333+00:00

Hello 浩明島田

Thanks for responding back on this.

I am not able to understand the screenshot shared. However, Microsoft Q&A currently supports English only.

I would request you to open a support case for further assistance on this.

浩明島田 20 Reputation points

2023-03-07T12:49:51.7666667+00:00
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浩明島田 20 Reputation points

2023-03-07T12:49:06.92+00:00
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vipullag-MSFT 24,441 Reputation points

2023-03-07T16:29:43.0033333+00:00

Hello 浩明島田

Responding here with more details.

Apologies for confusion. You cannot set JIT on uniform VMSS however, looks like you can set JIT on Flex:

Yes, it is possible to SSH into a uniform mode or flexible mode instance using Azure CLI.

What is the reason for limited functionality in uniform mode instances?

I wouldn't say it is "limited functionality." Uniform is the legacy VMSS type. You can't do certain things because the VMSS instances are controlled from the VMSS model.

Hope this helps.

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