fix(gke): point web backend health check at /login (no healthy upstream)

[gaurav0107]

Symptom

https://langprobe.daz.co.in/ returns "no healthy upstream" even though the tracebility-web pod is Running and 1/1 Ready.

Root cause

The GCP L7 LB provisioned by the tracebility-web Gateway was health-checking the web backend at path /. Next.js returns 307 → /login at / (signed-in routing). GCP backend health checks treat anything other than 2xx as UNHEALTHY, so the backend NEG sat perma-UNHEALTHY and the LB returned 503s.

A prior fix (commit 31d8f81 "point web probes at /login") fixed the kubelet-side livenessProbe / readinessProbe, but the LB-side health check is configured separately — by default the GKE Gateway controller derives it from the backend Service and falls back to / on port 7090. The override mechanism is HealthCheckPolicy.networking.gke.io targeting the Service.

$ gcloud compute backend-services get-health gkegw1-1b53-tracebility-tracebility-web-7090-xbgwu0fpd8mr --global
... healthState: UNHEALTHY
... ipAddress: 10.7.0.98
... port: 7090

Fix

Add deploy/k8s/gke-gateway/healthcheckpolicy.yaml:

apiVersion: networking.gke.io/v1
kind: HealthCheckPolicy
spec:
  default:
    config:
      type: HTTP
      httpHealthCheck: { port: 7090, requestPath: /login }
  targetRef:
    kind: Service
    name: tracebility-web

Updated README.md to document the file alongside gateway.yaml / httproute.yaml.

Verified live

• Applied the policy via kubectl apply -f.
• gcloud compute health-checks describe … confirms requestPath: /login.
• Backend health flipped UNHEALTHY → HEALTHY ~45s after apply.
• curl -sI https://langprobe.daz.co.in/login → 200.
• curl -sI https://langprobe.daz.co.in/ → 307 (correct Next redirect, not the LB 503).

Test plan

• CI on this PR goes green (no app-code change; just yaml + a docs hunk).
• Merge.
• Subsequent helm-deploy rollouts that recreate the Service don't lose the policy (HealthCheckPolicy is namespaced and survives Service recreation as long as the targetRef name stays tracebility-web).

🤖 Generated with Claude Code