FEAT(blackbox-exporter): add external endpoint monitoring

- Add blackbox-exporter with prometheus-community Helm chart
- Configure HTTP probes for 25 external endpoints
- Include SSL certificate expiry alerting rules
- Add probe failure and slow response alerts
- Deploy 2 replicas with anti-affinity for HA

blackbox-exporter/helm-values.yaml

@@ -0,0 +1,186 @@
+# Prometheus Blackbox Exporter Helm Values
+# Chart: https://github.com/prometheus-community/helm-charts/tree/main/charts/prometheus-blackbox-exporter
+
+fullnameOverride: blackbox-exporter
+
+replicas: 2
+
+resources:
+  requests:
+    cpu: 15m
+    memory: 64Mi
+  limits:
+    memory: 64Mi
+
+config:
+  modules:
+    http_2xx:
+      prober: http
+      timeout: 10s
+      http:
+        valid_http_versions: ["HTTP/1.1", "HTTP/2.0"]
+        valid_status_codes: [200, 301, 302, 303]
+        method: GET
+        follow_redirects: true
+        preferred_ip_protocol: ip4
+        tls_config:
+          insecure_skip_verify: false
+    http_2xx_insecure:
+      prober: http
+      timeout: 10s
+      http:
+        valid_http_versions: ["HTTP/1.1", "HTTP/2.0"]
+        valid_status_codes: [200, 301, 302, 303]
+        method: GET
+        follow_redirects: true
+        preferred_ip_protocol: ip4
+        tls_config:
+          insecure_skip_verify: true
+    tcp_connect:
+      prober: tcp
+      timeout: 5s
+    icmp:
+      prober: icmp
+      timeout: 5s
+      icmp:
+        preferred_ip_protocol: ip4
+
+serviceMonitor:
+  enabled: true
+  defaults:
+    additionalMetricsRelabels: {}
+    interval: 60s
+    scrapeTimeout: 30s
+    module: http_2xx
+  additionalLabels:
+    release: prometheus
+  targets:
+    # Infrastructure Services
+    - name: argocd
+      url: https://argocd0213.kro.kr
+      module: http_2xx
+    - name: grafana
+      url: https://grafana0213.kro.kr
+      module: http_2xx
+    - name: vault
+      url: https://vault0213.kro.kr
+      module: http_2xx
+    - name: authelia
+      url: https://auth0213.kro.kr
+      module: http_2xx
+    - name: karma
+      url: https://karma0213.kro.kr
+      module: http_2xx
+    - name: gitea
+      url: https://github0213.com
+      module: http_2xx
+    - name: minio-console
+      url: https://minio0213.kro.kr
+      module: http_2xx
+    - name: velero-ui
+      url: https://velero0213.kro.kr
+      module: http_2xx
+    - name: headlamp
+      url: https://kubernetes0213.kro.kr
+      module: http_2xx
+    - name: goldilocks
+      url: https://goldilocks0213.kro.kr
+      module: http_2xx
+    - name: code-server
+      url: https://vscode0213.kro.kr
+      module: http_2xx
+    - name: pgweb
+      url: https://pgweb0213.kro.kr
+      module: http_2xx
+    - name: zot
+      url: https://zot0213.kro.kr
+      module: http_2xx
+
+    # User Applications
+    - name: homer
+      url: https://mayne.kro.kr
+      module: http_2xx
+    - name: portfolio
+      url: https://minjo0213.kro.kr
+      module: http_2xx
+    - name: docusaurus
+      url: https://docusaurus0213.kro.kr
+      module: http_2xx
+    - name: jotion
+      url: https://jotion0213.kro.kr
+      module: http_2xx
+    - name: jovies
+      url: https://jovies.kro.kr
+      module: http_2xx
+    - name: todo
+      url: https://todo0213.kro.kr
+      module: http_2xx
+    - name: umami
+      url: https://umami0213.kro.kr
+      module: http_2xx
+    - name: mas
+      url: https://mas0213.kro.kr
+      module: http_2xx
+    - name: jaejadle
+      url: https://jaejadle.kro.kr
+      module: http_2xx
+    - name: jaejadle-dev
+      url: https://dev.jaejadle.kro.kr
+      module: http_2xx
+    - name: joossam
+      url: https://joossameng.kro.kr
+      module: http_2xx
+    - name: joossam-dev
+      url: https://dev.joossameng.kro.kr
+      module: http_2xx
+
+prometheusRule:
+  enabled: true
+  additionalLabels:
+    release: prometheus
+  rules:
+    - alert: BlackboxProbeFailed
+      expr: probe_success == 0
+      for: 5m
+      labels:
+        severity: critical
+      annotations:
+        summary: "Blackbox probe failed for {{ $labels.target }}"
+        description: "Probe {{ $labels.instance }} has been failing for more than 5 minutes."
+    - alert: BlackboxSlowProbe
+      expr: avg_over_time(probe_duration_seconds[5m]) > 5
+      for: 5m
+      labels:
+        severity: warning
+      annotations:
+        summary: "Blackbox slow probe for {{ $labels.target }}"
+        description: "Probe {{ $labels.instance }} took more than 5s to complete."
+    - alert: BlackboxSslCertificateWillExpireSoon
+      expr: (probe_ssl_earliest_cert_expiry - time()) / 86400 < 30
+      for: 1h
+      labels:
+        severity: warning
+      annotations:
+        summary: "SSL certificate will expire soon for {{ $labels.target }}"
+        description: "SSL certificate expires in {{ $value | humanizeDuration }} for {{ $labels.instance }}."
+    - alert: BlackboxSslCertificateExpired
+      expr: (probe_ssl_earliest_cert_expiry - time()) <= 0
+      for: 5m
+      labels:
+        severity: critical
+      annotations:
+        summary: "SSL certificate has expired for {{ $labels.target }}"
+        description: "SSL certificate has expired for {{ $labels.instance }}."
+
+affinity:
+  podAntiAffinity:
+    preferredDuringSchedulingIgnoredDuringExecution:
+      - weight: 100
+        podAffinityTerm:
+          labelSelector:
+            matchExpressions:
+              - key: app.kubernetes.io/name
+                operator: In
+                values:
+                  - prometheus-blackbox-exporter
+          topologyKey: kubernetes.io/hostname