When a client requests resource-load information, the S Series Node returns statistics for storage, CPU, and bandwidth usage. If no request has been made for this information in the past minute, the S Series Node uses values from both server modules to calculate the applicable statistics. The S Series Node returns the calculated statistics to the client and also caches the individual server-module values and the calculated statistics in memory. If the S Series Node receives the same request within one minute after the last request, the S Series Node responds with the cached calculated statistics.
The S Series Node sends a timestamp with each response to the client. The timestamp is the earlier of the times when the applicable values were provided by each server module. The older the timestamp is, the less reliable the statistics are.
If a server module has not updated its values for three or more minutes, the values are considered stale. If the values for only one server module are stale, the S Series Node uses the cached values for that server module and the current values for the other server module to calculate the resource-load statistics. In this case, the S Series Node does not update the timestamp, so the timestamp returned with the statistics is the time when the server module with the stale values last updated those values.
If the values for both server modules are stale, the S Series Node returns the cached statistics to the client. In this case, the timestamp returned with the statistics is the earlier of the times each server module last updated the applicable values.
If a server module is unavailable when the S Series Node receives a request for resource-load information, the S Series Node uses default values for that server module and the current values for the other server module to calculate the resource-load statistics. In this case, the S Series Node returns an updated timestamp with the statistics.
After a restart of the S Series Node, until both server modules have finished their startup processing, a request for resource-load information returns an HTTP 503 (Service Unavailable) status code.