For some reason, the *zincati.service* unit has an `After=` dependency
on *multi-user.target*. This creates a dependency loop between
*local_exporter.service* and *zincati.service* if the former has an
`After=` dependency on the latter an an (implicit) `Before=` dependency
on *multi-user.target*. systemd will resolve this loop by removing one
or the other units from the bootup sequence, so either Zincati or the
local exporter will not start at boot.
We can avoid this dependency loop by removing the `After=` dependency
from *local_exporter.service*. This may cause requests for Zincati
metrics to fail if it happens to come in after the local exporter starts
but before Zincati does, but this is unlikely to actually be an issue.
Zincati provides Prometheus metrics via a Unix socket. In order for
these to be scraped by `vmagent`, they need to be exposed over HTTP.
The `local_exporter` is designed to do specifically this.
Unfortunately, the Zincati metrics socket is only accessible by the
*zincati* user, so the `local_exporter` also needs to run as that user.
Hopefully, the user ID will remain consistent in future versions of
CoreOS.
Dustin