生產環境常見的HTTP狀態碼列表-轉自（老男孩）
200 - OK，服務器成功返回網頁
- Standard response for successful HTTP requests.
301 - Moved Permanently（永久跳轉），請求的網頁已永久跳轉到新位置。
- This and all future requests should be directed to the given.
403 - Forbidden（禁止訪問）,服務器拒絕請求
- forbidden request (matches a deny filter) => HTTP 403
- The request was a legal request, but the server is refusing to respond to it.
404 - Not Found,服務器找不到請求的頁面。
- The requested resource could not be found but may be available again in the future.
500 - Internal Server Error（內部服務器錯誤）
- internal error in haproxy => HTTP 500
- A generic error message, given when no more specific message is suitable.
502 - Bad Gateway（壞的網關）,一般是網關服務器請求後端服務時，後端服務沒有按照http協議正確返回結果。
- the server returned an invalid or incomplete response => HTTP 502
- The server was acting as a gateway or proxy and received an invalid response from the upstream server.
503 - Service Unavailable（服務當前不可用）,可能因爲超載或停機維護。
- no server was available to handle the request => HTTP 503
- The server is currently unavailable (because it is overloaded or down for maintenance).
504 - Gateway Timeout（網關超時）,一般是網關服務器請求後端服務時，後端服務沒有在特定的時間內完成服務。
- the server failed to reply in time => HTTP 504
- The server was acting as a gateway or proxy and did not receive a timely response from the upstream server.