## What this PR does
Adds an opt-in `publishing.exposure=loadBalancer` mode for the
ingress-nginx Service as a migration path away from
`Service.spec.externalIPs`, which is deprecated upstream in Kubernetes
v1.36
([KEP-5707](https://github.com/kubernetes/enhancements/issues/5707),
[kubernetes#137293](https://github.com/kubernetes/kubernetes/pull/137293)).
The `AllowServiceExternalIPs` feature gate is expected to default to off
around v1.40 and the implementation to be removed around v1.43.
Stacked on top of #2464 (cilium v1.19.3 bump) — depends on it for the
`CiliumLoadBalancerIPPool` at `cilium.io/v2`.
### Behavior
- New platform value `publishing.exposure` — enum `externalIPs |
loadBalancer`, default `externalIPs` (current behavior unchanged on
upgrade).
- Plumbed through `cozystack-values` into each tenant's ingress
HelmRelease via the new `expose-mode` key.
- When `exposure=loadBalancer` and the current namespace matches
`publishing.ingressName`, the Service becomes `type: LoadBalancer` with
`externalTrafficPolicy: Local` and a `CiliumLoadBalancerIPPool`
announces the addresses from `publishing.externalIPs` via Cilium LB
IPAM.
- The pool uses a namespace-only `serviceSelector`
(`io.kubernetes.service.namespace: <ns>`) — any LoadBalancer Service in
the tenant namespace draws from it. See "Pool ownership" below.
- IPv4 addresses get `/32` CIDRs, IPv6 addresses get `/128`. Mixed
families supported. Pre-CIDR entries (`192.0.2.10/32`) are accepted
without double-suffixing.
- Unknown values, `loadBalancer` with empty externalIPs, and stray empty
entries from `publishing.externalIPs` are rejected at render time with
explicit error messages.
### Pool ownership
The `CiliumLoadBalancerIPPool` is rendered from
`packages/apps/tenant/templates/cilium-lb-pool.yaml`, not from the
ingress chart. The tenant chart is the per-tenant owner of cross-cutting
resources (Namespace, `cozystack-values` Secret, HelmReleases for
ingress and gateway), so one pool per tenant lives there.
Cilium LB IPAM rejects overlapping CIDRs across pools regardless of
`serviceSelector` — the last-added pool gets `cilium.io/PoolConflict`
and stops allocating. Keeping the pool in the ingress chart would
collide with the Gateway-API PR (#2470), which materialises its own
LoadBalancer Service from the same `publishing.externalIPs` range when
`tenant.spec.gateway=true`. Moving the pool to the tenant chart with a
namespace-only selector lets a single pool back both services
(ingress-nginx today, a Cilium Gateway Service once #2470 lands).
Only the ingress-loadBalancer signal is wired here
(`_cluster.expose-mode=loadBalancer` + `.Values.ingress=true` +
publishing tenant). #2470 rebases on top of this PR, drops its own
`packages/extra/gateway/templates/cilium-lb-pool.yaml`, and adds an OR
branch for `.Values.gateway` in the tenant template.
### Scope
Only the ingress-nginx Service is migrated by this setting. Other
cozystack components that still write `Service.spec.externalIPs`
directly (notably the `vpn` app at
`packages/apps/vpn/templates/service.yaml`) need separate follow-up
before Kubernetes v1.40.
### Tests
- `packages/extra/ingress/tests/exposure_test.yaml` — 10 helm-unittest
cases on the ingress-nginx Service: type / externalTrafficPolicy /
externalIPs assertion for both modes, unknown-mode rejection
(case-sensitive enum), empty-IPs failure, empty-entry filtering,
non-publishing-tenant fallback.
- `packages/apps/tenant/tests/exposure_test.yaml` — 9 cases on the pool
itself: IPv4, IPv6, mixed, pre-CIDR input, empty-entry filtering,
`ingress=false` in publishing tenant (no pool), non-publishing tenant
(no pool), empty externalIPs (no pool).
- Both suites are auto-discovered by `hack/helm-unit-tests.sh` via the
`test:` target in each package's Makefile.
### Caveats (copied from the inline `values.yaml` comment)
- `loadBalancer` mode uses `externalTrafficPolicy: Local`. The external
IP must already be routed to a node that hosts an ingress pod (floating
IP / upstream router / podAntiAffinity).
- Cilium does not announce the IP on its own unless L2 announcements or
BGP are enabled in the Cilium values (disabled by default in cozystack).
- Switching the value on a running cluster causes the ingress-nginx
Service to be recreated (`upgrade.force: true` on the HelmRelease +
Service kind change); expect a brief interruption of ingress traffic.
### Release note
```release-note
feat(ingress): add opt-in publishing.exposure=loadBalancer mode that uses type: LoadBalancer + CiliumLoadBalancerIPPool instead of the deprecated Service.spec.externalIPs. Default (externalIPs) preserves existing behavior.
```
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