Troubleshoot the "UnsatisfiablePDB" error during an AKS cluster upgrade

2024-04-10

This article discusses how to identify and resolve the "UnsatisfiablePDB" error that might occur when you try to upgrade an Azure Kubernetes Service (AKS) cluster.

Prerequisites

This article requires Azure CLI version 2.53.0 or a later version. Run az --version to find your installed version. If you need to install or upgrade the Azure CLI, see How to install the Azure CLI.

Symptoms

An AKS cluster upgrade operation fails with the following error message:

Code: UnsatisfiablePDB
Message: 1 error occurred:
* PDB <pdb-namespace>/<pdb-name> has maxunavailble == 0 can't proceed with put operation

Cause

Before starting an upgrade operation, AKS checks the cluster for any existing Pod Disruption Budgets (PDBs) that have the maxUnavailable parameter set to 0. Such PDBs are likely to block node drain operations. If node drain operations are blocked, the cluster upgrade operation can't complete successfully. This might potentially cause the cluster to be in a failed state.

After receiving the "UnsatisfiablePDB" error, you can confirm the PDB's status by running the following command:

$ kubectl get pdb <pdb-name> -n <pdb-namespace>

The output of this command should be similar to the following one:

NAME         MIN AVAILABLE   MAX UNAVAILABLE   ALLOWED DISRUPTIONS   AGE
<pdb-name>   N/A             0                 0                     49s

If the value of MAX UNAVAILABLE is 0, the node drain fails during the upgrade process.

To resolve this issue, use one of the following solutions.

Solution 1: Adjust the PDB's "maxUnavailable" parameter

Note

Use this solution if you can edit the PDB resource directly.

Set the PDB's maxUnavailable parameter to 1 or a greater value. For more information, see Specifying a PodDisruptionBudget.
Retry the AKS cluster upgrade operation.

Solution 2: Back up, delete, and redeploy the PDB

Note

Use this solution if directly editing the PDB resource isn't viable.

Back up the PDB using the following command:

$ kubectl get pdb <pdb-name> -n <pdb-namespace> -o yaml > pdb_backup.yaml

Delete the PDB using the following command:

$ kubectl delete pdb <pdb-name> -n <pdb-namespace>

Retry the AKS cluster upgrade operation.
If the AKS cluster upgrade operation succeeds, redeploy the PDB using the following command:
```
$ kubectl apply -f pdb_backup.yaml
```

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.

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