HTTP response status and possible cause of probblem

Things that can be inferred from the HTTP response status


HTTP response statustypeWhat can be guessed
404Not FoundRequestMapping is incorrect The 
URL is incorrect
503Service Unavailable 
Service Temporarily Unavailable
I can not access it due to limitations on the number of simultaneous connections of hosting server
502Bad GatewayMalfunction of user side gateway or 
website side proxy server