Use protobuf encoding for core K8s APIs in external-attacher

[tosi3k]

What type of PR is this?
/kind feature

What this PR does / why we need it:
If not specified explicitly, JSON encoding is used by default when talking to kube-apiserver.

For core K8s API objects like Pods, Nodes, etc., we can use protobuf encoding which reduces CPU consumption related to (de)serialization, reduces overall latency of the API call, reduces memory footprint, reduces the amount of work performed by the GC and results in quicker propagation of objects to event handlers of shared informers.

Which issue(s) this PR fixes:
No issue is opened for that.

Special notes for your reviewer:
Standard system components of K8s default their serialization method to protobuf for some time already:

• kube-scheduler: link
• kubelet: link
• kube-proxy: link
• kube-controller-manager: link and method's contents

Some benchmarks comparing JSON vs. protobuf showcasing how the latter data format (de)serializes faster and uses less memory:

• https://medium.com/@akresling/go-benchmark-json-v-protobuf-4ec3c62ec8d4
• https://www.codingexplorations.com/blog/performance-comparison-protobuf-marshaling-vs-json-marshaling-in-go
• https://medium.com/@david_turner/protocol-buffers-just-how-fast-are-they-9ec19ea580db

Does this PR introduce a user-facing change?:

NONE

[k8s-ci-robot]

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[k8s-ci-robot]

Hi @tosi3k. Thanks for your PR.

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[tosi3k]

/assign @msau42

[jsafrane]

/ok-to-test

[jsafrane]

@tosi3k All the other Kubernetes components you linked have protobuf configurable, while your PR makes them hardcoded. Is there a case when a cluster admin or CSI driver vendor would need to switch back to JSON?

[tosi3k]

@tosi3k All the other Kubernetes components you linked have protobuf configurable, while your PR makes them hardcoded. Is there a case when a cluster admin or CSI driver vendor would need to switch back to JSON?

The only case coming up to my mind is when someone would use CSI-related sidecars in a K8s cluster which doesn't have protobuf encoding supported.

That theoretical case is not possible in practice, though, because CSI project is younger than protobuf support in K8s:

• CSI support was added as an alpha feature in K8s 1.9: https://kubernetes.io/blog/2019/01/15/container-storage-interface-ga/.
• Protobuf encoding support is embedded in kube-apiserver in K8s 1.3+ and can't be turned off.

[jsafrane]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jsafrane, tosi3k

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