SERVICE_UNAVAILABLE constant
int
const SERVICE_UNAVAILABLE
The server is not ready to handle the request.
Common causes are a server that is down for maintenance or that is overloaded. Note that together with this response, a user-friendly page explaining the problem should be sent.
This responses should be used for temporary conditions and the Retry-After: HTTP header should, if possible, contain the estimated time before the recovery of the service.
The webmaster must also take care about the caching-related headers that are sent along with this response, as these temporary condition responses should usually not be cached.
Implementation
static const int SERVICE_UNAVAILABLE = 503;