為了從 ingress 的設定下手，我們將更動從 ALB 改成 ingress，方法就是使用變數的設定來做切換。首先，我們先定義不同的 rule 對應到的 target group

inMaintenanceMode: false
rules:
  - name: "abc"
    hostPrefix: "abc"
    paths:
      - path: "/*"
        serviceName: "abc-api-service"
        servicePort: 80

###############
# Maintenance #
###############
maintenanceRules:
  - name: "abc-maintenance-1"
    hostPrefix: "abc"
    paths:
      - path: "/"
        serviceName: "abc-maintenance-rule-1"
        servicePort: 80
  - name: "abc-maintenance-2"
    hostPrefix: "abc"
    paths:
      - path: "/"
        serviceName: "abc-maintenance-rule-2"
        servicePort: 80

  - name: "abc-maintenance-3"
    hostPrefix: "abc"
    paths:
      - path: "/"
        serviceName: "abc-maintenance-rule-3"
        servicePort: 80
  
  - name: "maintenanceCode"
    hostPrefix: "abc"
    paths:
      - path: "/"
        serviceName: "maintenance-503"
        servicePort: 80

為什麼類似的 Name 要建立多個，是因為我們有特定的白名單要加入，這些白名單是為了讓 QA Team 可以在 maintenance mode 的時候如預期進入服務內做測試。

完成之後，再來要到 template 裡面進行設定

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: {{ .Release.Namespace }}-ingress
  namespace: {{ .Release.Namespace }}
  annotations:
    ##############################
    # maintenance mode - abc #
    ##############################
    alb.ingress.kubernetes.io/conditions.abc-maintenance-rule-1 : {{ .Values.maintenanceIpAddress1 | toJson | quote }}
    alb.ingress.kubernetes.io/actions.abc-maintenance-rule-1 : {{ .Values.maintenanceRules  | toJson | quote  }}
 
    alb.ingress.kubernetes.io/actions.maintenance-503: >
        {"type":"fixed-response","fixedResponseConfig":{"contentType":"text/plain","statusCode":"503","messageBody":"maintenance mode"}}

spec:
  rules:
  # maintenance rules
  {{- $inMaintenanceMode := .Values.inMaintenanceMode  -}}
  {{- if $inMaintenanceMode }}
  {{- range .Values.maintenanceRules }}
  {{- else }}
  - http:
        pathType: Prefix
        backend:
          service:
            name: {{ .serviceName }}
            port:
              name: use-annotation
      {{- end }}
  {{- end }}
  # if not inMaintenanceMode
  {{- else }}
  # default rules
  {{- range .Values.rules }}
  - http:
        pathType: Prefix
        backend:
          service:
            name: {{ .serviceName }}
            port: 
              number: {{ .servicePort }}
      {{- end }}
  {{- end }}
  {{- end }}

如此一來，我們就可以藉由切換變數的 inMaintenanceMode 來切換模式了！