Sometimes, the web server partially closes down due to temporary overload, or maintenance.
503 errors in the HTTP cycle
Any client goes through the following cycle when it communicates with the web server.
- Obtain an IP address from the IP name of the site (the site URL without the leading 'http://'). This lookup (conversion of IP name to IP address) is provided by domain name servers (DNSs).
- Open an IP socket connection to that IP address.
- Write an HTTP data stream through that socket.
- Receive an HTTP data stream back from the Web server in response. This data stream contains status codes whose values are determined by the HTTP protocol. Parse this data stream for status codes and other useful information.
Fixing 503 errors
The web server effectively shuts down - "Closed for Repair" - although it still functions minimally enough to communicate the 503 status code. Full service is impossible at this time. When you see a 503 error, you can rest assured that human intervention is current, and that it will not be long until service is resumed.
Phoning you ISP to determine why the service is down, could be fruitful.