metrics: introduce metrics based on the NNS

[mkowalski]

This PR introduces a small set of metrics based on the NodeNetworkState, i.e. kubernetes_nmstate_network_interfaces and
kubernetes_nmstate_routes. Those track number of network interfaces and number of routes for every node in the cluster where nmstate handler pods are running.

This creates a skeleton for k-nmstate to create metrics based on the effective state of the network on the system and not only based on the content of NNCP.

In the future it may be used to create statistics about network topologies of clusters.

Is this a BUG FIX or a FEATURE ?:

Uncomment only one, leave it on its own line:

/kind bug
/kind enhancement

What this PR does / why we need it:

Special notes for your reviewer:

Release note:

New metrics `kubernetes_nmstate_network_interfaces` and `kubernetes_nmstate_routes` are introduced to track number of network interfaces and number of routes configured per node.

[kubevirt-bot]

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[gemini-code-assist]

Summary of Changes

Hello @mkowalski, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the observability of network configurations within the cluster by introducing new Prometheus metrics derived directly from the NodeNetworkState. These metrics provide a granular view of network interfaces by type and routes by IP stack and configuration type (static/dynamic) on each node. This foundational work lays the groundwork for future capabilities, such as analyzing network topologies and gaining deeper insights into the operational state of the network.

Highlights

• New Metrics Introduction: Two new Prometheus metrics, "kubernetes_nmstate_network_interfaces" and "kubernetes_nmstate_routes", have been introduced to provide detailed insights into the network configuration of nodes.
• NodeNetworkState-based Monitoring: A dedicated controller (NodeNetworkStateReconciler) now actively monitors NodeNetworkState objects to collect and update these new metrics, ensuring they reflect the current network reality.
• Interface and Route Counting Logic: New utility functions ("CountInterfacesByType", "CountRoutes") have been added to parse NodeNetworkState and accurately count network interfaces by type and routes by IP stack (IPv4/IPv6) and type (static/dynamic).
• Comprehensive Testing: Extensive unit tests for the new counting logic and end-to-end tests for the metrics themselves have been added to ensure accuracy and reliability.

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[gemini-code-assist]

Code Review

This pull request introduces new Prometheus metrics to track network interface counts by type and network route counts by node, IP stack, and type (static/dynamic). A new NodeNetworkStateReconciler controller was added to manage these metrics, watching NodeNetworkState objects and updating kubernetes_nmstate_network_interfaces and kubernetes_nmstate_routes gauges based on the node's current network state. The controller uses in-memory maps to track previous interface types and route keys, enabling the cleanup of stale metrics when network configurations change or are deleted. Helper functions for counting interfaces and routes were added to pkg/state/filter.go, necessitating updates to pkg/state/type.go for proper data unmarshaling. Extensive unit and E2E tests were included to validate the new metrics. A review comment highlighted that the in-memory state for tracking old metrics could lead to temporary inaccuracies after controller restarts, a common consideration for Prometheus controllers.

[mkowalski]

[mkowalski]

/test pull-kubernetes-nmstate-e2e-handler-k8s