Graph object count per object storage backend

We need an estimate of the current object count in all our object storage backends, and ideally to have some trend graphs on this data.

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Migrated from T1607 (view on Phabricator)

assigned to @olasd

marked this issue as related to #1599 (closed)

added Metrics/monitoring Sprint 2019 03 priority:High labels

https://grafana.softwareheritage.org/d/jScG7g6mk/objstorage-object-counts shows the data that we're currently able to collect.

The Grafana Azure metrics data source is not great (30 days history only, data full of random holes, no aggregation capabilities, ...) so I'm considering using the Prometheus Azure metrics exporter (https://github.com/RobustPerception/azure_metrics_exporter) to properly pull the data into prometheus. The current status of that is...

 azure.go         | 24 ++++++++++++------------
 config/config.go |  2 ++
 main.go          | 26 ++++++++++++++------------
 utils.go         |  2 +-
 4 files changed, 29 insertions(+), 25 deletions(-)

added state:wip label