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Troubleshoot ZonalAllocationFailed, AllocationFailed, or OverconstrainedAllocationRequest error code

This article describes how to identify and resolve the ZonalAllocationFailed, AllocationFailed, or OverconstrainedAllocationRequest error that might occur when you try to create, deploy, or update a Microsoft Azure Kubernetes Service (AKS) cluster.

Prerequisites

  • Azure CLI (optional), version 2.0.59 or a later version. If Azure CLI is already installed, you can find the version number by using az --version.

  • Azure PowerShell (optional).

Symptoms

When you try to create an AKS cluster, you receive the following error message:

Reconcile vmss agent pool error: VMSSAgentPoolReconciler retry failed:

Category: InternalError;

SubCode: ZonalAllocationFailed;

Dependency: Microsoft.Compute/VirtualMachineScaleSet;

OrginalError: Code="ZonalAllocationFailed"

Message="Allocation failed. We do not have sufficient capacity for the requested VM size in this zone. Read more about improving likelihood of allocation success at https://aka.ms/allocation-guidance";

AKSTeam: NodeProvisioning

Or, when you try to upgrade or scale up a cluster, you receive the following error message:

Code="OverconstrainedAllocationRequest"

Message="Allocation failed. VM(s) with the following constraints cannot be allocated, because the condition is too restrictive. Please remove some constraints and try again."

Or, when you use dedicated hosts in a cluster and try to create or scale up a node pool, you receive the following error message:

Code="AllocationFailed"

Message="Allocation failed. VM allocation to the dedicated host failed. Please ensure that the dedicated host has enough capacity or try allocating elsewhere."

Cause 1: Limited zone availability in a SKU

You're trying to deploy, upgrade or scale up a cluster in a zone that has limited availability for the specific SKU.

Solution 1: Use a different SKU, zone, or region

Try one or more of the following methods:

  • Redeploy the cluster in the same region by using a different SKU.
  • Redeploy the cluster in a different zone in that region.
  • Redeploy the cluster in a different region.
  • Create a new node pool in a different zone or use a different SKU.

For more information about how to fix this error, see Resolve errors for SKU not available.

Cause 2: Too many constraints for a virtual machine to accommodate

If you receive an OverconstrainedAllocationRequest error code, the Azure Compute platform can't allocate a new virtual machine (VM) to accommodate the required constraints. These constraints usually (but not always) include the following items:

  • VM size
  • VM SKU
  • Accelerated networking
  • Availability zone
  • Ephemeral disk
  • Proximity placement group (PPG)

Solution 2: Don't associate a proximity placement group with the node pool

If you receive an OverconstrainedAllocationRequest error code, you can try to create a new node pool that isn't associated with a proximity placement group.

Cause 3: Not enough dedicated hosts or fault domains

You're trying to deploy a node pool in a dedicated host group that has limited capacity or doesn't satisfy the fault domain constraint.

Solution 3: Ensure you have enough dedicated hosts for your AKS nodes/VMSS

As per Planning for ADH Capacity on AKS, you're responsible for planning enough dedicated hosts to span as many fault domains as required by your AKS VMSS. For example, if the AKS VMSS is created with FaultDomainCount=2, you need at least two dedicated hosts in different fault domains (FaultDomain 0 and FaultDomain 1).

More information

Ensuring capacity for users is a top priority for Microsoft, and we're working around the clock to reach this goal. The increasing popularity of Azure services emphasizes the need to scale up our infrastructure even more rapidly. With that in mind, we're expediting expansions and improving our resource deployment process to respond to strong customer demand. We're also adding a large amount of computing infrastructure monthly.

We have identified several methods to improve how we load-balance under a high-resource-usage situation and how to trigger the timely deployment of needed resources. Additionally, we're significantly increasing our capacity and will continue to plan for strong demand across all regions. For more information about the improvements that we're making toward delivering a resilient cloud supply chain, see Advancing reliability through a resilient cloud supply chain.

References

Contact us for help

If you have questions or need help, create a support request, or ask Azure community support. You can also submit product feedback to Azure feedback community.