nginx front and backend config on same server

default

server {
        root /var/www/xxx;
        index index.html;
        server_name xxx.xxx;
         if ($request_method = 'OPTIONS') {
                add_header 'Access-Control-Allow-Origin' '*';
                add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';
                add_header 'Access-Control-Allow-Headers' 'DNT,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Range';
                add_header 'Access-Control-Max-Age' 1728000;
                add_header 'Content-Type' 'text/plain; charset=utf-8';
                add_header 'Content-Length' 0;
                return 204;
         }
         if ($request_method = 'POST') {
          add_header 'Access-Control-Allow-Origin' '*';
          add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';
          add_header 'Access-Control-Allow-Headers' 'DNT,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Range';
          add_header 'Access-Control-Expose-Headers' 'Content-Length,Content-Range';
         }
         if ($request_method = 'GET') {
          add_header 'Access-Control-Allow-Origin' '*';
          add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';
          add_header 'Access-Control-Allow-Headers' 'DNT,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Range';
          add_header 'Access-Control-Expose-Headers' 'Content-Length,Content-Range';
         }
       location / {
          try_files $uri $uri/ =404;
       }
       location /api {
           proxy_pass http://localhost:5000;
           proxy_set_header Host $host;
       }
}