Use a full real-world example that is compatible with the omnibus
dashboards and follows Prometheus best practices.

Marcel Amirault authored 5 years ago and Achilleas Pipinellis committed 5 years ago

Many code blocks are 4spaced, and they render in GitLab
without coloring as a result, even though they are
fenced with a language label. If in a list, other items
will render as being in a code block too, even if not
meant to. This fixes all these issues for many admin
docs (part 2)

Updated to include missing metrics:
    * GitLab Workhorse
    * Nginx
    * Sidekiq

* Update metric names to match current release.
* Improve descriptions.
* Improve examples to show more query language functionality.

Memory:
* Show use of `or` function.
* Automatically select "MemAvailable" kernel metric if possible.

CPU:
* Show use of `avg without ...`.
* Show CPU utilization per node.

Network:
* Show use of `!=` label matching.
* Don't show "localhost" metrics.

Update index.md to describe leaving out the host in prometheus['listen_address'] to allow public access.

Signed-off-by: Rémy Coutable <remy@rymai.me>

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Reported in https://gitlab.com/gitlab-org/omnibus-gitlab/issues/1905

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