google-cloud-platform - API Gateway が backendRequest のホスト名を「dev.equipment.example.com:443」ではなく「backend-cluster-dev.equipment.example.com:443」に変更する

Question

API Gateway がホスト名の先頭に「backend-cluster」プレフィックスを追加する理由を理解できません。リクエストのゲートウェイのログは次のようになります。

{
    httpRequest: {
        latency: "0.113s"
        protocol: "HTTP/1.1"
        remoteIp: "5.20.198.209"
        requestMethod: "GET"
        requestUrl: "https://XXX.nw.gateway.dev/organizations/XXXXXXXXX/export?period=0"
        responseSize: "221"
        status: 503
        userAgent: "PostmanRuntime/7.28.4"
    }
    insertId: "5cf296ad774f8088eeb7ed100ecc4498-1@a2"
    jsonPayload: {
        api: "//apigateway.googleapis.com/projects/XXXXXXX/locations/global/apis/eu-dev-XXX-api"
        apiConfig: "//apigateway.googleapis.com/projects/XXXXXXXX/locations/global/apis/eu-dev-XXX-api/configs/config"
        apiKey: "XXXXXXXXXXXXXXXXX"
        apiMethod: "1.eu_dev_XXX_api_XXXXXXXXXXX_apigateway_XXX_dev_XXXXXXX_cloud_goog.GetExport"
        backendRequest: {
            duration: "0ms"
            hostname: "**backend-cluster-**dev.equipment.example.com:443"
            path: "/api/v1/XXXXXXX/organizations/XXXXXXXXXX/export?period=0"
        }
        consumerNumber: "XXXXXX"
        responseDetails: "upstream_reset_before_response_started{connection_failure,TLS_error:_268435581:SSL_routines:OPENSSL_internal:CERTIFICATE_VERIFY_FAILED}"
    }
    logName: "projects/XXXXXXX/logs/apigateway.googleapis.com%2Frequests"
    receiveTimestamp: "2021-10-25T08:48:03.222779242Z"
    resource: {
        labels: {
            gateway_id: "XXXXXXXX"
            location: "europe-west2"
            resource_container: "projects/XXXXXX"
        }
        type: "apigateway.googleapis.com/Gateway"
    }
    timestamp: "2021-10-25T08:47:51.184895263Z"
}

ゲートウェイの構成は次のように単純です。

# openapi2-run.yaml
swagger: '2.0'
info:
  title: Export API
  description: This API gateway is used to access export API functionality
  version: 1.0.0
schemes:
  - https
produces:
  - application/json
securityDefinitions:
  api_key_header:
    type: apiKey
    name: x-api-key
    in: header
paths:
  /organizations/{org_id}/export:
    get:
      summary: Organisation export API endpoint
      operationId: getExport
      x-google-backend:
        address: **https://dev.equipment.example.com/api/v1/XXXXXXXX**
        protocol: http/1.1
        path_translation: APPEND_PATH_TO_ADDRESS
      parameters:
        - in: "path"
          name: "org_id"
          description: "The organization identifier"
          required: true
          type: "string"
      security:
        - api_key_header: []
      responses:
        '200':
          description: A successful response
          schema:
            type: object

アイデアにより、リダイレクトは https://dev.equipment.example.com/api/v1/XXXXXXXX/organizations/XXXXXXXXXX/export?period=0 に移動する必要がありますが、代わりにhttps://backend-cluster-dev.equipmentに移動します.example.com/api/v1/XXXXXXXX/organizations/XXXXXXXXXXX/export?period=0もちろん失敗します。

なぜそれが起こるのか、何か考えはありますか？

前もって感謝します！