When running carbon-cache daemon, clients are seeing errors such as connection refused by the daemon, a common reason for this is setting small number of file descriptors.
/var/log/carbon/console.log file, there may be
exceptions.IOError: [Errno 24] Too many open files: '/var/lib/graphite/whisper/systems/<host_name>/<metric_name>.wsp'
The number of files carbon-cache daemon can open should be increased. Many Linux systems set file descriptors to a maximum of 1024 as default. A value of 16384 may be good enough depending on how many clients are simultaneously connecting to the carbon-cache daemon.
In Linux, sysctl and ulimit programs can be used to set system-wide resource use.