Azure / Azure/bicep-registry-modules
[AVM Module Issue]: Instance Mix for Virtual Machine Scale Sets
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Description
### Check for previous/existing GitHub issues
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### Issue Type?
Feature Request
### Module Name
avm/res/compute/virtual-machine-scale-set
### (Optional) Module Version
_No response_
### Description
On April 22, 2025, Microsoft announced [General Availability of Instance Mix for Virtual Machine Scale Sets (VMSS) with Flexible Orchestration Mode](https://techcommunity.microsoft.com/blog/azurecompute/general-availability-instance-mix-for-virtual-machine-scale-sets-with-flexible-o/4406386/)—a highly anticipated feature enabling users to define a mix of VM sizes in flexible orchestration mode for better cost and performance optimization.
Currently, this feature is not supported in the Azure Verified Modules (AVM) for virtual machine scale sets, which limits adoption of this capability via infrastructure as code (IaC) using the AVM ecosystem.
**Expected Behavior:**
AVM modules (e.g., [avm-res-compute-virtualmachinescaleset](https://github.com/Azure/bicep-registry-modules/tree/main/avm/res/compute/virtual-machine-scale-set) should allow configuration of [instanceMix](https://learn.microsoft.com/en-us/azure/virtual-machine-scale-sets/instance-mix-overview).
**Use Case:**
Organizations using AVM modules for deploying production workloads would benefit from:
- Greater flexibility in workload placement
- Cost optimization by mixing on-demand and spot instances
- Better resiliency using diverse VM SKUs
**References:**
- [Azure Update - GA: Instance Mix for VMSS Flexible Orchestration Mode (April 22, 2025)](https://techcommunity.microsoft.com/blog/azurecompute/general-availability-instance-mix-for-virtual-machine-scale-sets-with-flexible-o/4406386)
- [Azure Docs: Use instance mix in flexible orchestration](https://learn.microsoft.com/en-us/azure/virtual-machine-scale-sets/instance-mix-overview)
**Request:**
Please add support for this capability in the AVM VMSS module.
Thanks in advance for considering this request!
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