Hello @Joao Silva ,
Thanks for reaching out to Microsoft QnA. Happy to answer your question.
You can place the entire cluster consisting of your VMs under an existing or new resource group. All the VMs in the same cluster should be placed under the same resource group as far as I know.
Please check point 3 in this document for your reference, and let me know if you have questions. Please feel free to tag me in your reply. Thank You.
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