Parece que o caminho node_exporter não está correto.
ExecStart=/usr/bin/node_exporter
Eu tenho outro caminho para isso no Ubuntu 16.04
~# cat /etc/issue
Ubuntu 16.04.3 LTS \n \l
~# which node_exporter
/usr/sbin/node_exporter
Se não for a raiz do problema, verifique seu /var/log/syslog
. Deve mostrar o motivo da falha, algo semelhante a:
Oct 20 12:30:30 prom systemd[8848]: node_exporter.service: Failed at step EXEC spawning /usr/bin/node_exporter: No such file or directory
Oct 20 12:30:30 prom systemd[1]: node_exporter.service: Main process exited, code=exited, status=203/EXEC
Oct 20 12:30:30 prom systemd[1]: node_exporter.service: Unit entered failed state.
Oct 20 12:30:30 prom systemd[1]: node_exporter.service: Failed with result 'exit-code'.
Oct 20 12:30:30 prom systemd[1]: node_exporter.service: Service hold-off time over, scheduling restart.
Oct 20 12:30:30 prom systemd[1]: Stopped Prometheus exporter for machine metrics, written in Go with pluggable metric collectors..
Oct 20 12:30:30 prom systemd[1]: Started Prometheus exporter for machine metrics, written in Go with pluggable metric collectors..