Paperless-ngx uses a Celery task to process uploaded files, converting
them to PDF, running OCR, etc. This task can be marked as "failed" for
various reasons, most of which are more about the document itself than
the health of the application. The GUI displays the results of failed
tasks when they occur. It doesn't really make sense to have an alert
about this scenario, especially since there's nothing to do to directly
clear the alert anyway.
Fedora CoreOS fills `/boot` beyond the 75% alert threshold under normal
circumstances on aarch64 machines. This is not a problem, because it
cleans up old files on its own, so we do not need to alert on it.
Unfortunately, the _DiskUsage_ alert is already quite complex, and
adding in exclusions for these devices would make it even worse.
To simplify the logic, we can use a recording rule to precomupte the
used/free space ratio. By using `sum(...) without (type)` instead of
`sum(...) on (df, instance)`, we keep the other labels, which we can
then use to identify the metrics coming from machines we don't care to
monitor.
Instead of having different thresholds for different volumes
encoded in the same expression, we can use multiple alerts to alert on
"low" vs "very low" thresholds. Since this will of course cause
duplicate alerts for most volumes, we can use AlertManager inhibition
rules to disable the "low" alert once the metric crosses the "very low"
threshold.
The `flower_events_total` metric is a counter, so its value only ever
increases (discounting restarts of the server process). As such,
nonzero values do not necessarily indicate a _current_ problem, but
rather that there was one at some point in the past. To identify
current issues, we need to use the `increase` function, and then apply
the `max_over_time` function so that the alert doesn't immediately reset
itself.
After the incident this week with the CPU overheating on _vmhost1_, I
want to make sure I know as soon as possible when anything is starting
to get too hot.
Patroni, a component of the *postgres poerator*, exports metrics about
the PostgreSQL database servers it manages. Notably, it provides
information about the current transaction log location for each server.
This allows us to monitor and alert on the health of database replicas.
I did not realize the batteries on the garage door tilt sensors had
died. Adding alerts for various sensor batteries should help keep me
better informed.
Graylog is down because Elasticsearch corrupted itself again, and this
time, I'm just not going to bother fixing it. I practically never use
it anymore anyway, and I want to migrate to Grafana Loki, so now seems
like a good time to just get rid of it.
If Frigate is running but not connected to the MQTT broker, the
`sensor.frigate_status` entity will be available, but the
`update.frigate_server` entity will not.
Since *mtrcs0.pyrocufflink.blue* (the Metrics Pi) seems to be dying,
I decided to move monitoring and alerting into Kubernetes.
I was originally planning to have a single, dedicated virtual machine
for Victoria Metrics and Grafana, similar to how the Metrics Pi was set
up, but running Fedora CoreOS instead of a custom Buildroot-based OS.
While I was working on the Ignition configuration for the VM, it
occurred to me that monitoring would be interrupted frequently, since
FCOS updates weekly and all updates require a reboot. I would rather
not have that many gaps in the data. Ultimately I decided that
deploying a cluster with Kubernetes would probably be more robust and
reliable, as updates can be performed without any downtime at all.
I chose not to use the Victoria Metrics Operator, but rather handle
the resource definitions myself. Victoria Metrics components are not
particularly difficult to deploy, so the overhead of running the
operator and using its custom resources would not be worth the minor
convenience it provides.
Dustin