Add Guidance wrt Labelling to Naming and Rules Best Practices

docs/practices/naming.md

@@ -80,7 +80,18 @@ the underlying metric type and unit you work with.
 * **Metric collisions**: With growing adoption and metric changes over time, there are cases where lack
 of unit and type information in the metric name will cause certain series to collide (e.g. `process_cpu` for seconds and milliseconds).
 
-## Labels
+### Important Labels
+
+* `job`
+   * The `job` label is a primary key to differentiate metrics from each other.
+   * If not specified in PromQL expressions, they will match unrelated metrics with the same name. This is especially true in a multi system or multi tenant installation
+
+WARNING: When using `without`, be careful not to strip out the `job` label accidentally.
+
+* `instance`
+   * The `instance` label will include the `ip:port` what was scraped, providing a crucial breadcrumb for debugging scrape time issues
+
+### General Labelling Advice
 
 Use labels to differentiate the characteristics of the thing that is being measured:
 

docs/practices/rules.md

@@ -19,6 +19,8 @@ This page documents proper naming conventions and aggregation for recording rule
 Keeping the metric name unchanged makes it easy to know what a metric is and
 easy to find in the codebase.
 
+IMPORTANT: `job` label acts as a primary key. It is **strongly** recommended that you use it to scope your PromQL expressions to the system you are monitoring.
+
 To keep the operations clean, `_sum` is omitted if there are other operations,
 as `sum()`. Associative operations can be merged (for example `min_min` is the
 same as `min`).
@@ -27,6 +29,18 @@ If there is no obvious operation to use, use `sum`.  When taking a ratio by
 doing division, separate the metrics using `_per_` and call the operation
 `ratio`.
 
+## Labels
+
+NOTE: Omitting a label in a PromQL expression is the functional equivalent of specifying `label=*`
+
+* In both recorded rules and alerting expressions, always specify a `job` label to prevent expression mismatches from occuring.
+  This is especially important in multi-tenant systems where the same metric names may be exported by different jobs or the
+  same job (e.g `node_exporter) in multiple, distinct deployments
+
+* Always specify a `without` clause with the labels you are aggregating away.
+This is to preserve all the other labels such as `job`, which will avoid
+conflicts and give you more useful metrics and alerts.
+
 ## Aggregation
 
 * When aggregating up ratios, aggregate up the numerator and denominator
@@ -40,10 +54,6 @@ Instead keep the metric name without the `_count` or `_sum` suffix and replace
 the `rate` in the operation with `mean`. This represents the average
 observation size over that time period.
 
-* Always specify a `without` clause with the labels you are aggregating away.
-This is to preserve all the other labels such as `job`, which will avoid
-conflicts and give you more useful metrics and alerts.
-
 ## Examples
 
 _Note the indentation style with outdented operators on their own line between