# Variables and Dashboard Design — Prometheus + Grafana

Source: https://www.skillbyai.com/en/prometheus-grafana/g-variables

> One dashboard, many services.

## Template variables and layout

Dashboard **variables** make dashboards reusable: a `job` variable populated by `label_values(up, job)` and an `instance` variable that depends on it let one dashboard serve every service. Use them in queries as `$job`. Lay out dashboards top-down: key health indicators (traffic, errors, latency, saturation) in the first row, details below, and link to drill-down dashboards. Add descriptions to panels so newcomers know what each one means.

## Variable queries

Grafana Prometheus variable definitions.

```text
job       label_values(up, job)
instance  label_values(up{job="$job"}, instance)      (multi-value, include All)
route     label_values(http_requests_total{job="$job"}, route)

Panel query using multi-value variables:
  sum by (instance) (rate(http_requests_total{job="$job", instance=~"$instance"}[$__rate_interval]))
```

## Use =~ with multi-value variables

Multi-select variables expand to a regex such as (a|b), so match them with =~.

**Quiz:** What does label_values(up, job) provide for a variable?

- [ ] The number of jobs
- [x] The list of job label values found on the up metric
- [ ] A PromQL alert
- [ ] A new data source

*Answer:* The list of job label values found on the up metric. Populates dropdown options.