Expose read-only DiscoverReadOnly() API for library consumers

[mchmarny]

Context

We are integrating k8s-launch-kit into NVIDIA/aicr as a Go library — see tracking epic NVIDIA/aicr#827 and Phase 1 NVIDIA/aicr#828.

AICR's snapshot pipeline has a strict Collector contract: read-only, bounded, no cluster mutation, no required RBAC beyond list/get on standard objects. Today's l8k discovery flow does not fit this contract.

Problem

(*NetworkOperatorPlugin).DiscoverClusterConfig (pkg/networkoperatorplugin/discovery.go:99-260) is a mutating operation:

1. Patches/creates NicClusterPolicy to stand up nic-configuration-daemon.
2. Execs into those daemon pods to read /sys/module, nvidia-smi, etc.
3. Reads NicDevice CRs.
4. Patches node labels (nvidia.kubernetes-launch-kit.machine=…).
5. Defer-cleanup of the patch.

Even ignoring the cluster-state changes, downstream collectors that import this code would inherit pod-exec RBAC and a hard dependency on network-operator being installed first.

The good news: discovery.go:112-126 already contains a reuseExisting short-circuit that does exactly the right thing when nic-configuration-daemon is already running — it skips the CR patch and proceeds straight to reading the daemons.

Request

Expose a stable, read-only entry point, e.g.:

// Package: github.com/nvidia/k8s-launch-kit/pkg/networkoperatorplugin

// DiscoverReadOnly inspects an existing nic-configuration-daemon DaemonSet
// (and the NicDevice CRs it has populated) and returns the discovered
// cluster topology. It does NOT create or modify any cluster resources.
//
// Returns ErrNotInstalled if network-operator's nic-configuration-daemon
// is not running in the cluster.
func DiscoverReadOnly(ctx context.Context, c client.Client) (*config.LaunchKubernetesConfig, error)

Behavior:

• Use the existing reuseExisting branch when daemons are present.
• Return a sentinel ErrNotInstalled (or similar) when not.
• Never patch NicClusterPolicy. Never patch node labels. Never create CRs.
• Pod-exec is acceptable (it's read-only against a pre-existing daemon), but document the RBAC requirement clearly.

Why this helps l8k

• Clean library contract for downstream tools beyond AICR.
• Decouples "discovery" from "deployment of the nic-configuration-daemon" — a useful separation in its own right.
• Existing CLI flow can call DiscoverReadOnly first, fall back to today's mutating flow if it returns ErrNotInstalled.

Open questions

• Naming / package placement: pkg/networkoperatorplugin.DiscoverReadOnly keeps it close to the existing code. A leaf package (pkg/discovery/readonly) with thinner deps would be even better for downstream library users — willing to discuss.
• Module dep cost for library consumers: importing pkg/networkoperatorplugin today pulls Mellanox/network-operator, Mellanox/nic-configuration-operator, controller-runtime, etc. If the read-only path could live in a leaf package without the Mellanox CRD type imports, that would meaningfully reduce vendor cost downstream.
• Versioning: any plan for a v1.0.0 tag? Library consumers would prefer to pin by semver rather than by SHA.

Happy to contribute the implementation if the API shape is acceptable.