Multiple virtual clusters in managed instance subnet?

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Multiple virtual clusters in managed instance subnet?

David C 191

Is it OK to deploy more than one MI per subnet?

When adding 2nd, 3rd, etc. MI's to one subnet, is a new virtual cluster created, or the original one used? I'll try adding multiple MI's and observe for myself, but at the moment, waiting another team's collaboration before I can proceed.

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Answer 1

GeethaThatipatri-MSFT 29,542 Microsoft Employee Moderator

Hi, @David C Thanks for posting your question in the Microsoft forum.

Thanks, @Alberto Morillo for your contribution and for providing the detailed information.

Yes, you can as long as you have enough IP addresses. This outlines how to calculate how many you need and unless you are using pools it will spin up clusters under the covers Determine required subnet size & range - Azure SQL Managed Instance | Microsoft Learn

Regards
Geetha

David C 191 Reputation points

2022-02-08T23:19:57.54+00:00

Thank you Geetha. We don't have any MI's in production yet. But I have one in test where I gave the subnet the entire 256 IPs. My concern with adding multiple MI's in one subnet, is whether there would be cross-MI performance hit or outage during maintenance operations because of virtual cluster expansion.
GeethaThatipatri-MSFT 29,542 Reputation points Microsoft Employee Moderator

2022-02-09T22:01:33.293+00:00

Hi, @DavidC-7877There are many users who put multiple MI's in a subnet without any issues. each instance has its own resource governance. Also as this is not a pool, the resources are allocated at the instance level so they are not shared across the instances. Each instance has its own underlying nodes etc.

Please don't forget to click on or upvote button whenever the information provided helps you. Original posters help the community find answers faster by identifying the correct answer.

Regards
Geetha
GeethaThatipatri-MSFT 29,542 Reputation points Microsoft Employee Moderator

2022-02-10T17:27:31.463+00:00

Thank you @David C for visiting Microsoft QA forums! Have a great day!

Regards
Geetha

Answer 2

Alberto Morillo 34,671 MVP Volunteer Moderator

Creating a dedicated VNET for each managed instance is optional. If you want to have only one subnet in your Virtual Network (Virtual Network blade will enable you to define first subnet called default ), you need to know that Managed Instance subnet can have between 16 and 256 addresses. Therefore, use subnet masks /28 to /24 when defining your subnet IP ranges for default subnet. If you know how many instances you will have make sure that you have at least 2 addresses per instance + 5 system addresses in the default subnet.

Subnet is dedicated to Managed Instance and cannot contain any other resource (i.e. Azure VMs should not be placed in that subnet.)

David C 191 Reputation points

2022-02-08T23:31:14.4+00:00

Thank you Alberto. I have a MI in one subnet of 256 IPs in one vnet in a test subscription. I gave the subnet all 256 for fear of running out of IPs with a smaller range and multiple MI's. Been a while since I deployed my test MI. As i recall, I deleted the "default" subnet, and created a new one with my preferred naming convention. I just hope deleting "default" didn't break anything. I would think that Azure would have stopped me from deploying MI in other than "default" if it wasn't allowed. Bottom line, does the first default subnet need to be left?
Alberto Morillo 34,671 Reputation points MVP Volunteer Moderator

2022-02-09T00:14:44.147+00:00

No. You can delete the VNET if not needed on your deployments.

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Multiple virtual clusters in managed instance subnet?

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