Common Status Codes

status code	Detailed description
200～OK	The server successfully returns the web page, which is a successful http request and returns the standard status code
301-Moved Permanently	Permanent jump, all requested web pages will be permanently jumped to the new location set, for example: jump from baidu.com to www.baidu.com
403-Forbidden	Access is prohibited. This request is legal, but the server refuses to respond to the client's request because it matches the preset rules. Such problems are generally caused by improper configuration of server or service permissions.
404-Not Found	The server cannot find the specified page requested by the client, which may be caused by the client requesting a resource that does not exist on the server
500-Internal Server Error	Internal server error, the server encountered an unexpected condition and was unable to fulfill the client's request. This is a more general error, usually caused by server settings or internal program problems. For example, SElinux is enabled, but no rule permission is set for http, client access is 500
502-Bad Gateway (emphasis)	A bad gateway is generally when a proxy server requests a back-end service, but the back-end service is unavailable or fails to respond to the gateway server. It is generally caused by a problem with the node under the reverse proxy server.
503-Service Unavailable	The service is currently unavailable, possibly because the server is overloaded or down for maintenance, or there is no node behind the reverse proxy server that can provide the service
504-Gateway Timeout	The gateway times out. Generally, when the gateway proxy server requests the back-end service, the back-end service does not complete the processing request within a specific time. Generally, the server is overloaded and does not return data to the front-end proxy server within the specified time.
For a blog post on common HTTP status codes in production environments, see http://oldboy.blog.51cto.com/2561410/716294