CNI should respect eniConfig label if it already exists.

[backjo]

What happened:

We currently have a set of nodes that use custom networking. As part of a new application being deployed, we want to give the pods on these nodes an ENIConfig that is different from the ENIConfig for other nodes in the cluster (which is set based on AZ). To try and achieve this, we provided userdata to this set of nodes to have the kubelet set an initial eniConfig label.

When the nodes start up, they are re-labeled by the CNI with the value of the label specified in ENI_CONFIG_LABEL_DEF (which ends up mapping to an AZ)

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What you expected to happen:
I'd expect the CNI to respect the eniConfig label if it already set on the node.
How to reproduce it (as minimally and precisely as possible):
Set the eniConfig label in the kubelet configuration. Start and join the node to a K8S cluster with the CNI installed. Notice that the label is modified.
Anything else we need to know?:

I noticed that a workaround for this is possible by specifying the annotation, but from a user perspective, that's much harder to control/set compared to labels - labels can be set via kubelet options, whereas the annotation would need to be set by some controller or other component.

Environment:

• Kubernetes version (use kubectl version): 1.21
• CNI Version: 1.9.0
• OS (e.g: cat /etc/os-release): BottleRocket 1.2.0
• Kernel (e.g. uname -a):