Juju prometheus Ceph exporter charm

Based on https://github.com/digitalocean/ceph_exporter

Introduction and Preparation

The charm implements ceph-exporter functionality for Prometheus, it consumes the prometheus-ceph-exporter snap package,
Charm needs to be deployed where Ceph is running, a special read-only account ("exporter") will be created by the charm.
Since the snap is confined to his own filesystem, ceph config file and "exporter" keyring will be created in ($SNAP_DATA) :

/var/snap/prometheus-ceph-exporter/current/

How to Deploy:

From the MAAS host:

export JUJU_REPOSITORY=$PWD/charms
export INTERFACE_PATH=$PWD/interfaces

Build the charm

charm build -s xenial

Deploy the charm

juju deploy local:xenial/prometheus-ceph-exporter

To change the port, refer to the daemon_arguments provided by the snap package at:
/var/snap/prometheus-ceph-exporter/current/daemon_arguments