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Troubleshoot Node Not Ready failures if there are expired certificates

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This article helps you troubleshoot Node Not Ready scenarios within a Microsoft Azure Kubernetes Service (AKS) cluster if there are expired certificates.

Prerequisites

Symptoms

You discover that an AKS cluster node is in the Node Not Ready state.

Cause

There are one or more expired certificates.

Prevention: Run OpenSSL to sign the certificates

Check the expiration dates of certificates by invoking the openssl-x509 command, as follows:

  • For virtual machine (VM) scale set nodes, use the az vmss run-command invoke command:

    az vmss run-command invoke \
    --resource-group <resource-group-name> \
    --name <vm-scale-set-name> \
    --command-id RunShellScript \
    --instance-id 0 \
    --output tsv \
    --query "value[0].message" \
    --scripts "openssl x509 -in /etc/kubernetes/certs/apiserver.crt -noout -enddate"

  • For VM availability set nodes, use the az vm run-command invoke command:

    az vm run-command invoke \
    --resource-group <resource-group-name> \
    --name <vm-availability-set-name> \
    --command-id RunShellScript \
    --output tsv \
    --query "value[0].message" \
    --scripts "openssl x509 -in /etc/kubernetes/certs/apiserver.crt -noout -enddate"

You might receive certain error codes after you invoke these commands. For information about error codes 50, 51, and 52, see the following links, as necessary:

If you receive error code 99, this indicates that the apt-get update command is being blocked from accessing one or more of the following domains:

  • security.ubuntu.com
  • azure.archive.ubuntu.com
  • nvidia.github.io

To allow access to these domains, update the configuration of any blocking firewalls, network security groups (NSGs), or network virtual appliances (NVAs).

Solution: Rotate the certificates

You can apply certificate auto rotation to rotate certificates in the nodes before they expire. This option requires no downtime for the AKS cluster.

If you can accommodate cluster downtime, you can manually rotate the certificates instead.

Note

Starting in the July 15, 2021, release of AKS, an AKS cluster upgrade automatically helps to rotate the cluster certificates. However, this behavioral change doesn't take effect for an expired cluster certificate. If an upgrade takes only the following actions, the expired certificates won't be renewed:

  • Upgrade a node image.
  • Upgrade a node pool to the same version.
  • Upgrade a node pool to a more recent version.

Only a full upgrade (that is, an upgrade for both the control plane and the node pool) helps renew the expired certificates.

More information