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Monitoring Kubernetes Gateway API with Vigilmon: Gateway Health, HTTPRoute Sync, Backend Connectivity & TLS Certificate Alerts

How to monitor Kubernetes Gateway API with Vigilmon — Gateway status health checks, HTTPRoute sync error detection, backend service connectivity, TLS certificate expiry, and traffic routing reliability.

The Kubernetes Gateway API is the next-generation standard for ingress, traffic routing, and service mesh configuration in Kubernetes, replacing the older Ingress resource with a role-oriented, extensible model built around Gateway, HTTPRoute, GRPCRoute, and TLSRoute resources. When a Gateway loses its attached HTTPRoutes, traffic stops reaching your backend services — silently, with no application-level error. When the Gateway controller (Envoy Gateway, NGINX Gateway Fabric, Istio, or another implementation) crashes, all routing configuration stops reconciling and new deployments receive no traffic. When a backend service referenced in an HTTPRoute goes unhealthy, the Gateway may continue accepting requests and returning 502s without any visible alert. Vigilmon gives you external visibility into the traffic routing layer: Gateway availability, backend service health, TLS certificate expiry, and the reliability of every HTTPRoute rule serving your users.

What You'll Build

  • HTTP monitors on each Gateway-fronted service to detect routing failures
  • Backend service health checks that identify which service caused a 502/503
  • TLS certificate monitoring for every hostname attached to a Gateway listener
  • TCP monitors on Gateway controller ports to detect implementation-level failures
  • An alerting runbook that maps Gateway API failure modes to the right Kubernetes resources to inspect

Prerequisites

  • A Kubernetes cluster with a Gateway API implementation installed (Envoy Gateway, NGINX Gateway Fabric, Istio, or Contour)
  • At least one Gateway resource configured with listeners and attached HTTPRoute resources
  • External access to your Gateway (LoadBalancer or NodePort service)
  • A free account at vigilmon.online

Step 1: Understand Gateway API's Health Surface

The Kubernetes Gateway API introduces conditions on Gateway and HTTPRoute resources that reflect reconciliation status. Check these before setting up external monitors:

# Check Gateway status conditions
kubectl get gateway production-gateway -n default -o jsonpath='{.status.conditions}' | jq .
# Look for: type=Programmed, status=True (Gateway is fully reconciled)
# Look for: type=Accepted, status=True (GatewayClass accepted this Gateway)

# Check HTTPRoute status
kubectl get httproute my-api-route -n production -o jsonpath='{.status.parents}' | jq .
# Look for: conditions[].type=Accepted, status=True
# Look for: conditions[].type=ResolvedRefs, status=True (all backend refs resolved)

A Gateway with Programmed=False means the controller has not successfully applied the routing configuration — traffic may be misrouted or rejected. An HTTPRoute with ResolvedRefs=False means one or more backend services referenced in the route do not exist or are in the wrong namespace.

For external monitoring, the most useful signals are:

  1. The HTTP response your users receive through the Gateway (end-to-end routing health)
  2. The health of each backend service the HTTPRoute points to
  3. TLS certificate validity for each Gateway listener hostname
  4. The Gateway controller's own health endpoint

Step 2: Monitor End-to-End Routing Through the Gateway

The most important monitor is an end-to-end HTTP check through the Gateway to your application. This validates the entire stack: Gateway listener, HTTPRoute matching, backend service resolution, and application response:

# Determine your Gateway's external IP
kubectl get gateway production-gateway -n default \
  -o jsonpath='{.status.addresses[0].value}'
# Returns: 203.0.113.45 (LoadBalancer IP)

# Test routing through the Gateway
curl -H "Host: api.example.com" https://api.example.com/health
  1. Log in to Vigilmon → Add Monitor → HTTP.
  2. URL: https://api.example.com/health (your application's health endpoint routed through the Gateway).
  3. Check interval: 60 seconds.
  4. Response timeout: 10 seconds.
  5. Expected status: 200.
  6. Keyword: your health response field (e.g., ok, healthy).
  7. Label: api.example.com (Gateway API routing).
  8. Click Save.

Add monitors for each distinct hostname attached to your Gateway. If your Gateway routes api.example.com, admin.example.com, and webhook.example.com, each needs its own Vigilmon monitor — a routing misconfiguration typically affects one hostname's HTTPRoute without touching the others.

Step 3: Monitor Backend Service Health Directly

Gateway API HTTPRoutes reference backend services by name. When a backend pod crashes, the Gateway starts returning 502s for that service while continuing to route other services normally. Monitor each backend service directly — in addition to the Gateway-routed endpoint — so you can distinguish a Gateway failure from a backend failure:

# Example HTTPRoute referencing two backends
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: api-route
  namespace: production
spec:
  parentRefs:
    - name: production-gateway
  hostnames:
    - "api.example.com"
  rules:
    - matches:
        - path:
            type: PathPrefix
            value: /orders
      backendRefs:
        - name: order-service
          port: 8080
    - matches:
        - path:
            type: PathPrefix
            value: /users
      backendRefs:
        - name: user-service
          port: 8080

For each backend service:

  1. Add Monitor → HTTP.
  2. URL: https://api.example.com/orders/health (the path routed to order-service).
  3. Check interval: 60 seconds.
  4. Response timeout: 10 seconds.
  5. Expected status: 200.
  6. Label: order-service (via Gateway API).
  7. Click Save.

Repeat for /users/health pointing to user-service.

502 vs. 503 distinction: A 502 Bad Gateway from your Gateway typically means the backend pod is returning an error or is unreachable. A 503 Service Unavailable often means no healthy backend pods exist (all pods failed readiness checks). Vigilmon's keyword check on a specific error message or JSON field can distinguish these cases when your app returns structured error bodies.

Step 4: Monitor for HTTPRoute Sync Errors

HTTPRoute sync failures happen when backend references are invalid, when cross-namespace ReferenceGrants are missing, or when the Gateway controller encounters a configuration error. While Vigilmon monitors the routing outcome, you should also alert on the Kubernetes conditions directly using a script or operator:

# Find all HTTPRoutes with ResolvedRefs=False (broken backend references)
kubectl get httproute -A -o json | jq '
  .items[] |
  select(
    .status.parents[].conditions[] |
    select(.type == "ResolvedRefs" and .status == "False")
  ) |
  {
    name: .metadata.name,
    namespace: .metadata.namespace,
    message: .status.parents[].conditions[] | select(.type == "ResolvedRefs") | .message
  }
'

Add this as a Kubernetes CronJob that alerts on failures:

apiVersion: batch/v1
kind: CronJob
metadata:
  name: gateway-route-health-check
  namespace: monitoring
spec:
  schedule: "*/5 * * * *"
  jobTemplate:
    spec:
      template:
        spec:
          containers:
            - name: checker
              image: bitnami/kubectl:latest
              command:
                - /bin/sh
                - -c
                - |
                  BROKEN=$(kubectl get httproute -A -o json | jq '[.items[] | select(.status.parents[].conditions[] | select(.type == "ResolvedRefs" and .status == "False"))] | length')
                  if [ "$BROKEN" -gt "0" ]; then
                    echo "ALERT: $BROKEN HTTPRoute(s) have broken backend references"
                    exit 1
                  fi
          restartPolicy: Never

Pair this CronJob alert with your Vigilmon HTTP monitors — when Vigilmon fires a 502 alert, check whether the corresponding HTTPRoute's ResolvedRefs condition explains the failure.

Step 5: Monitor TLS Certificate Expiry on Gateway Listeners

Gateway API listeners can terminate TLS using certificates stored as Kubernetes Secrets or referenced from external certificate managers. Certificate expiry on a Gateway listener causes all HTTPS traffic to that hostname to fail with a TLS handshake error — users see browser certificate warnings, and API clients get TLS errors:

# Example Gateway listener with TLS
spec:
  listeners:
    - name: https
      protocol: HTTPS
      port: 443
      hostname: "api.example.com"
      tls:
        mode: Terminate
        certificateRefs:
          - name: api-example-com-tls
            kind: Secret

For each Gateway listener hostname:

  1. Add Monitor → SSL Certificate.
  2. Domain: api.example.com.
  3. Alert when expiry is within: 30 days.
  4. Alert again: 14 days, 7 days, 3 days, 1 day.
  5. Click Save.

Repeat for every hostname attached to a Gateway listener. Common Gateway API deployments have multiple hostnames per Gateway — add one SSL monitor per hostname.

cert-manager and Gateway API: cert-manager's gateway-shim can automatically provision certificates for Gateway API listeners via cert-manager.io/cluster-issuer annotations on the Gateway resource. Auto-renewal failures are silent — the certificate appears valid until it suddenly expires. The 30-day alert threshold gives you time to investigate cert-manager events: kubectl get certificaterequests -A and kubectl describe challenge -A.

Step 6: Monitor the Gateway Controller

The Gateway controller (Envoy Gateway, NGINX Gateway Fabric, etc.) is the Kubernetes controller that translates Gateway API resources into data plane configuration. If the controller crashes or becomes unresponsive, routing configuration stops updating — new HTTPRoutes and backend changes stop taking effect:

Envoy Gateway:

kubectl -n envoy-gateway-system get pods -l control-plane=envoy-gateway
kubectl -n envoy-gateway-system port-forward svc/envoy-gateway 8081:8081 &
curl http://localhost:8081/healthz

NGINX Gateway Fabric:

kubectl -n nginx-gateway get pods -l app=nginx-gateway

For external monitoring of the Gateway controller metrics endpoint (if exposed):

  1. Add Monitor → HTTP.
  2. URL: https://envoy-gateway-metrics.example.com/metrics (if you expose the controller metrics externally).
  3. Check interval: 2 minutes.
  4. Expected status: 200.
  5. Label: Envoy Gateway controller.
  6. Click Save.

Additionally, monitor the data plane (Envoy proxy) via TCP:

  1. Add Monitor → TCP.
  2. Host: gateway.example.com (the Gateway's external LoadBalancer address).
  3. Port: 443.
  4. Check interval: 60 seconds.
  5. Label: Gateway data plane TCP (port 443).
  6. Click Save.

A TCP monitor on port 443 that fires while the HTTP monitor on the application endpoint also fails indicates a data plane failure. If only the HTTP monitor fires (TCP is green), the issue is in the routing configuration or backend services.

Step 7: Configure Alerting

In Vigilmon under Settings → Notifications, configure alert channels and response runbooks:

| Monitor | Trigger | Immediate action | |---|---|---| | Application endpoint via Gateway | Non-200 | Check kubectl get httproute -A; verify ResolvedRefs conditions; check backend pod health | | Backend service endpoint | Non-200 | Backend-specific failure; check pod logs: kubectl logs -n production -l app=order-service | | SSL certificate | < 30 days | Check cert-manager events; verify Gateway listener secret is current | | Gateway TCP (port 443) | Connection refused | Data plane failure; check Gateway controller pod; check LoadBalancer service health | | Gateway controller health | Non-200 | Controller not reconciling; new routing changes are not applying; check controller logs |

Alert grouping: Create a gateway-api monitor group containing all Gateway-related monitors. When a full Gateway failure occurs, all monitors fire together — the group view makes it immediately clear that the issue is at the Gateway layer rather than individual backends.

Common Gateway API Failure Modes and What Vigilmon Catches

| Scenario | Vigilmon signal | |---|---| | Gateway controller pod crash-loops | HTTP monitors start returning 502 (stale config) or timeout; TCP monitor may still pass | | HTTPRoute ResolvedRefs=False (deleted backend service) | Application endpoint returns 502; backend monitor also fires | | TLS certificate expires on Gateway listener | SSL monitor fires at 30-day threshold; HTTP monitor fires on expiry day | | Gateway LoadBalancer service loses external IP | TCP monitor fires; all HTTP monitors fire simultaneously | | Cross-namespace ReferenceGrant deleted | HTTPRoute stops routing traffic; application endpoint returns 502 or 404 | | Backend pod OOM killed | Backend health endpoint fires; Gateway returns 502 for affected paths | | New Gateway version upgrade breaks data plane | TCP may stay green; HTTP monitors fire if routing breaks | | Network policy blocks Gateway to backend traffic | Application endpoint returns 502; direct backend TCP stays green | | GatewayClass controller unavailable | Existing routing continues; new Gateways cannot be created (not externally visible) | | DNS misconfiguration for Gateway hostname | All monitors for that hostname fire simultaneously |

The Kubernetes Gateway API brings powerful, role-oriented traffic management to Kubernetes — but its distributed architecture means failures can occur at the controller, the data plane, the routing configuration, the backend services, or the TLS layer independently. Vigilmon gives you external visibility across all of these: end-to-end HTTP routing health through your Gateway, per-backend service availability, TLS certificate expiry for every listener hostname, and data plane TCP connectivity. When a misconfigured HTTPRoute or an expired certificate breaks traffic silently, Vigilmon alerts you before your users start complaining.

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