super naive open files check for datadog

fd.py

from checks import AgentCheck

class FileDescriptorCheck(AgentCheck):
    def check(self, instance):
        with open('/proc/sys/fs/file-nr', 'r') as fobj:
            fd_open, unknown, fd_max = fobj.read().split('\t')
            self.gauge('system.fd_open', int(fd_open))
            self.gauge('system.fd_max', int(fd_max))
            self.gauge('system.fd_open_pct', float(fd_open)/float(fd_max))

fd.yaml

init_config:
    nothing: 0
instances:
    [{}]