Move ingress traffic off the retired ingress-nginx controller onto Gateway API without a user-visible change, and keep a fast rollback until the old path is provably unused.

Read references/gateway-api.md before responding. It holds the implementation matrix, the ownership model, CRD channel rules, the ingress2gateway v1.2.0 annotation coverage table, cert-manager requirements, Flux layering, the seven-phase cutover, rollback by stage, and the troubleshooting table. The working layout is examples/fluxcd/basic-monorepo; a before/after pair for one Ingress is in examples/gateway-api.

This command is interactive by default. With no arguments, ask the three questions below, then run the matching mode. Never apply converted manifests or change DNS yourself: produce the change, the validation, and the rollback, and let the user run it.

Questions (no arguments)

Ask one at a time:

1. Where are you? assess (have ingress-nginx, not started) / convert (ready to translate) / scaffold (new cluster, no Ingress yet) / cutover (Gateway works, traffic not moved) / debug (a route or Gateway is not working) / review (check existing Gateway API config) / rollback
2. Which implementation? Envoy Gateway (default) / Cilium / Istio / NGINX Gateway Fabric / AWS Load Balancer Controller / undecided. If undecided, apply the "Choosing an implementation" table: pick by what the team already operates
3. How is the cluster delivered? Flux / Argo CD / Helm or kubectl directly

Mode dispatch

---

Mode: assess

1. Collect:

   kubectl get ingressclass
   # One row per Ingress annotation, keeping the resource identity and hosts,
   # so every annotation can be traced to the Ingress that carries it.
   # Columns: namespace, name, class, hosts, annotation, value. The value is
   # kept because several blockers are value-dependent (`rewrite-target: /$1`
   # uses a capture group; a snippet's body is what has to be redesigned).
   # @tsv escapes tabs and newlines, so a multi-line snippet stays on one row.
   # An Ingress with no nginx annotation still gets one row with "-".
   kubectl get ingress -A -o json | jq -r '
     .items[]
     | (.metadata.annotations // {}) as $a
     | [.metadata.namespace, .metadata.name,
        (.spec.ingressClassName // $a["kubernetes.io/ingress.class"] // "-"),
        ([.spec.rules[]?.host // "*"] | unique | join(","))] as $id
     | ([$a | to_entries[] | select(.key | startswith("nginx.ingress.kubernetes.io/")) | [.key, .value]]
        | if length == 0 then [["-", "-"]] else . end)[]
     | $id + . | @tsv' > ingress-inventory.tsv
   column -t -s $'\t' ingress-inventory.tsv
   # Cluster-wide count per annotation, to size the work
   kubectl get ingress -A -o json \
     | jq -r '.items[] | .metadata.annotations // {} | keys[]' \
     | grep '^nginx.ingress.kubernetes.io/' | sort | uniq -c | sort -rn
   # Controller-wide settings also change behaviour, not just annotations
   kubectl get configmap -A -l app.kubernetes.io/name=ingress-nginx -o yaml

2. Classify every annotation against the coverage table in references/gateway-api.md:
   • auto: ingress2gateway converts it to core Gateway API
   • decision: converted to an implementation-specific policy, or converted with different semantics (timeouts, IP ranges, regex)
   • blocked: warned-and-dropped or not recognised (configuration-snippet, server-snippet, auth, rate limiting). Each needs an owner and a design before conversion
3. Flag controller ConfigMap keys that set global behaviour (custom headers, timeouts, use-forwarded-headers, ssl-redirect). They do not appear on any Ingress and are the easiest to lose
4. Output a table: namespace, Ingress, host, class, annotations by category, owner, blocking yes/no. End with the count of blocked items. Do not proceed to convert while any item is blocked without an agreed decision

Mode: convert

1. Confirm assess has no open blocked items
2. Run, one namespace at a time:

   ingress2gateway print --providers=ingress-nginx --emitter=envoy-gateway \
     -n <namespace> > converted-<namespace>.yaml

   Use --emitter=standard for a non-Envoy implementation, and --ingress-nginx-ingress-class=<class> when the class is not nginx. Never pass --allow-experimental-gw-api on a standard-channel cluster
3. Treat every warning as a finding. List each one with the Ingress it came from
4. Rewrite for the shared-Gateway model:
   • Delete generated Gateway objects
   • Set each route's parentRefs to platform-gateway in envoy-gateway-system, with the right sectionName
   • Move TLS to a Gateway HTTPS listener per hostname (cert-manager requirement)
   • Bind each HTTPS listener's allowedRoutes to the namespace that owns its hostname (kubernetes.io/metadata.name)
   • Use the Service port number in backendRefs
5. Re-express each decision item (filter or policy) and show it next to the original annotation
6. Validate:

   kubeconform -strict -summary \
     -schema-location default \
     -schema-location 'https://raw.githubusercontent.com/datreeio/CRDs-catalog/main/{{.Group}}/{{.ResourceKind}}_{{.ResourceAPIVersion}}.json' \
     converted-<namespace>.yaml

7. State what is not covered by the converted output, plainly

Mode: scaffold

Generate the layout from examples/fluxcd/basic-monorepo, adapted to the answers:

1. CRDs: standard channel, applied as plain manifests, never through a Helm release (they exceed the 1 MiB release Secret). For Flux: one Kustomization per source with prune: false and deletionPolicy: Orphan: Gateway API config/crd/standard at the pinned tag, plus Envoy Gateway's charts/crds/crds/generated/ from the pinned chart artifact. Set crds.enabled: false on the controller chart
2. Controller: pinned exact version; at least two control-plane replicas in production
3. Data plane: at least two proxy replicas plus a PodDisruptionBudget in production. Never a PDB of minAvailable: 1 on one replica
4. GatewayClass and Gateway: one shared Gateway owned by the platform team. Port 80 from: Same (redirect and ACME only), HTTPS listeners from: Selector bound to the namespace that owns the hostname via kubernetes.io/metadata.name. Never from: All, and never one shared opt-in label across listeners: either lets a team claim another team's hostname. App namespaces are created in the platform layer, never by the app layer
5. Redirect: a platform-owned RequestRedirect route on port 80 with statusCode: 308
6. TLS: cert-manager v1.15+ with config.gatewayAPI.enabled: true, the cert-manager.io/cluster-issuer annotation on the Gateway, and the gatewayHTTPRoute HTTP-01 solver. cert-manager must start after the CRDs exist (its layer dependsOn the CRD Kustomizations)
7. Delivery: for Flux, three layers (infrastructure → infrastructure-configs → apps) with a healthCheckExprs entry on Gateway Programmed. For Argo CD, sync waves in the same order
8. NetworkPolicy: allow app ingress only from the proxy pods (namespace and pod selector)
9. Run bash examples/gateway-api/gateway-api-validate.sh against the adapted copy, or the kubeconform command above

Mode: cutover

Produce a per-hostname plan following the migration path in references/gateway-api.md:

1. Pre-flight: Gateway Programmed=True, every route Accepted=True and ResolvedRefs=True, every certificate Ready
2. TTL: lower the DNS TTL to 60s at least one old-TTL period before the switch
3. Shadow test each hostname against the new address without touching DNS:

   # The address can be an IP or a hostname (cloud LBs often publish a DNS name).
   # --connect-to accepts either and keeps the URL host for Host and TLS SNI;
   # --resolve only accepts an IP and fails to parse a hostname.
   NEW_ADDR=$(kubectl get gateway platform-gateway -n envoy-gateway-system -o jsonpath='{.status.addresses[0].value}')
   curl -sS -o /dev/null -w '%{http_code} %{time_total}\n' \
     --connect-to <host>:443:"$NEW_ADDR":443 https://<host>/<health-path>

   Compare status codes, key response headers, redirects and p99 latency with the old path
4. Order: lowest-risk hostname first; one hostname per change
5. Soak criteria: error rate and p99 within SLO for at least one full business cycle
6. Decommission gate: no requests on the old load balancer for the whole soak. Decommissioning is its own change, never the cutover change

Blast radius: one hostname per DNS change. Nothing else moves.

Mode: debug

1. Collect:

   kubectl get gatewayclass
   kubectl get gateway -A
   kubectl describe gateway <name> -n <namespace>
   kubectl get httproute <name> -n <namespace> -o yaml   # read .status.parents
   kubectl get certificate,certificaterequest -A
   kubectl get svc -n envoy-gateway-system
   kubectl logs -n envoy-gateway-system deploy/envoy-gateway --tail=100

2. Classify the layer: CRD/chart rendering (install fails, admission policy errors), reconciliation (Flux or Argo stuck, no matches for kind), runtime (route or Gateway conditions)
3. Read the condition reason and match it to the troubleshooting table in references/gateway-api.md (NotAllowedByListeners, NoMatchingListenerHostname, BackendNotFound, RefNotPermitted, AddressNotAssigned)
4. State the most likely root cause with the exact field to change, the corrected YAML, the verification command, and the rollback

Mode: review

Review in this order and separate critical findings from improvements:

1. Correctness: backendRefs use port numbers; listener hostnames cover route hostnames; every HTTPS listener has hostname, tls.mode: Terminate and certificateRefs; configs depend on CRDs
2. Security: no from: All on shared listeners; each HTTPS listener binds to the namespace owning its hostname, not a shared label; ReferenceGrants are as narrow as possible; NetworkPolicy admits only proxy pods; no experimental channel unless deliberate
3. Operational safety: CRDs are plain manifests that are never pruned or deleted with their owner; the controller chart does not install CRDs; proxy replicas ≥ 2 with a PDB in production; exact version pins; a Programmed health check
4. Portability: implementation-specific policies are listed and justified

Mode: rollback

Ask which stage was reached, then apply the rollback table in references/gateway-api.md:

Output format

Every mode ends with:

• Findings or changes, with exact files and fields
• Blast radius, in one line
• Validation, as commands to run
• Rollback, as the concrete step for the stage reached