Ingress 兼容前端https & http 跨域配置access-control-allow-origin

场景说明：

前端域名a.com访问后端b.com域名，其中b.com使用Ingress配置，需要支持http://a.com和https://a.com两种前端域名跨域方式访问b.com。

一、使用Ingress原生跨域Annotations配置只可满足其中一种情况

注意，官方最新的文档cors-allow-origin支持配置多个域名，但在我们使用的比较旧的版本0.32中配置两个直接被设置为*，导致失败

annotations:
  nginx.ingress.kubernetes.io/enable-cors: true
  nginx.ingress.kubernetes.io/cors-allow-origin: https://a.com
  # 或者 nginx.ingress.kubernetes.io/cors-allow-origin: http://a.com
  nginx.ingress.kubernetes.io/cors-allow-methods: *
  nginx.ingress.kubernetes.io/cors-allow-headers: *
  nginx.ingress.kubernetes.io/cors-allow-credentials: true

二、以上配置生成的nginx.conf片段

# Cors Preflight methods needs additional options and different Return Code
 if ($request_method = OPTIONS) {
          
   
         more_set_headers Access-Control-Allow-Origin: *;
         more_set_headers Access-Control-Allow-Credentials: true;
         more_set_headers Access-Control-Allow-Methods: *;
         more_set_headers Access-Control-Allow-Headers: *;
         more_set_headers Access-Control-Max-Age: 1728000;
         more_set_headers Content-Type: text/plain charset=UTF-8;
         more_set_headers Content-Length: 0;
         return 204;
 }

 more_set_headers Access-Control-Allow-Origin: *;
 more_set_headers Access-Control-Allow-Credentials: true;
 more_set_headers Access-Control-Allow-Methods: *;
 more_set_headers Access-Control-Allow-Headers: *;

三、根据自动生成的nginx.conf改为使用configuration-snippet配置

annotations:
    nginx.ingress.kubernetes.io/configuration-snippet: |
      if ($request_method = OPTIONS) { 
        more_set_headers "Access-Control-Allow-Origin: $http_origin"; 
        more_set_headers Access-Control-Allow-Credentials: true; 
        more_set_headers Access-Control-Allow-Methods: *;
        more_set_headers Access-Control-Allow-Headers: *;
        more_set_headers Access-Control-Max-Age: 1728000;
        more_set_headers Content-Type: text/plain charset=UTF-8;
        more_set_headers Content-Length: 0; 
        return 204; 
      }   
      more_set_headers "Access-Control-Allow-Origin: $http_origin"; 
      more_set_headers Access-Control-Allow-Credentials: true; 
      more_set_headers Access-Control-Allow-Methods: *; 
      more_set_headers Access-Control-Allow-Headers: *;
    nginx.ingress.kubernetes.io/ssl-redirect: false