fix instance key in exporters (#3356)

* fix instance key in exporters

* Add notes on using `prometheus.exporter` components in clustered Alloy instances

* Call out the change in the changelog.

* Improve wording.

* Move the note

* Improve wording

* PR feedback for docs

* PR feedback: add warning if potentially misusing exporters

* feedback

Author: thampiotr

CHANGELOG.md

@@ -10,6 +10,13 @@ internal API changes are not present.
 Main (unreleased)
 -----------------
 
+### Breaking changes
+
+- `prometheus.exporter.blackbox`, `prometheus.exporter.snmp` and `prometheus.exporter.statsd` now use the component ID instead of the hostname as
+  their `instance` label in their exported metrics. This is a consequence of a bug fix that could lead to a missing data when using the exporter
+  with clustering. If you would like to retain the previous behaviour, you can use `discovery.relabel` with `action = "replace"` rule to
+  set the `instance` label to `sys.env("HOSTNAME")`. (@thampiotr)
+
 ### Features
 
 - (_Experimental_) Additions to experimental `database_observability.mysql` component:

docs/sources/reference/components/prometheus/prometheus.exporter.cadvisor.md

@@ -14,6 +14,8 @@ title: prometheus.exporter.cadvisor
 
 The `prometheus.exporter.cadvisor` component collects container metrics using [cAdvisor](https://github.com/google/cadvisor).
 
+{{< docs/shared lookup="reference/components/exporter-clustering-warning.md" source="alloy" version="<ALLOY_VERSION>" >}}
+
 ## Usage
 
 ```alloy

docs/sources/reference/components/prometheus/prometheus.exporter.process.md

@@ -14,6 +14,8 @@ title: prometheus.exporter.process
 
 The `prometheus.exporter.process` component embeds the [`process_exporter`](https://github.com/ncabatoff/process-exporter) for collecting process stats from `/proc`.
 
+{{< docs/shared lookup="reference/components/exporter-clustering-warning.md" source="alloy" version="<ALLOY_VERSION>" >}}
+
 ## Usage
 
 ```alloy

docs/sources/reference/components/prometheus/prometheus.exporter.self.md

@@ -14,6 +14,8 @@ title: prometheus.exporter.self
 
 The `prometheus.exporter.self` component collects and exposes metrics about {{< param "PRODUCT_NAME" >}} itself.
 
+{{< docs/shared lookup="reference/components/exporter-clustering-warning.md" source="alloy" version="<ALLOY_VERSION>" >}}
+
 ## Usage
 
 ```alloy

docs/sources/reference/components/prometheus/prometheus.exporter.unix.md

@@ -19,6 +19,8 @@ For more information on collectors, refer to the [`collectors-list`](#collectors
 
 You can specify multiple `prometheus.exporter.unix` components by giving them different labels.
 
+{{< docs/shared lookup="reference/components/exporter-clustering-warning.md" source="alloy" version="<ALLOY_VERSION>" >}}
+
 ## Usage
 
 ```alloy

docs/sources/reference/components/prometheus/prometheus.exporter.windows.md

@@ -24,6 +24,8 @@ The `include` and `exclude` arguments are preferred going forward.
 
 [windows_exporter]: https://github.com/prometheus-community/windows_exporter/tree/{{< param "PROM_WIN_EXP_VERSION" >}}
 
+{{< docs/shared lookup="reference/components/exporter-clustering-warning.md" source="alloy" version="<ALLOY_VERSION>" >}}
+
 ## Usage
 
 ```alloy

docs/sources/shared/reference/components/exporter-clustering-warning.md

@@ -0,0 +1,17 @@
+---
+canonical: https://grafana.com/docs/alloy/latest/shared/reference/components/exporter-clustering-warning/
+description: Shared content, exporter clustering warning
+headless: true
+---
+
+{{< admonition type="note" >}}
+We do not recommend using this exporter with [clustering](../../../../get-started/clustering/) enabled.
+
+The default `instance` label set by this exporter is the hostname of the machine running {{< param "PRODUCT_NAME" >}}.
+{{< param "PRODUCT_NAME" >}} clustering uses consistent hashing to distribute targets across the instances.
+This requires the discovered targets to be the same and have the same labels across all cluster instances.
+
+If you do need to use this component in a cluster, use a dedicated `prometheus.scrape` component that's used to scrape
+this exporter and doesn't have clustering enabled. Alternatively, use `discovery.relabel` to set the `instance` label to a
+value that is the same across all cluster instances.
+{{< /admonition >}}

internal/component/prometheus/exporter/apache/apache.go

@@ -19,8 +19,9 @@ func init() {
 	})
 }
 
-func createExporter(opts component.Options, args component.Arguments, defaultInstanceKey string) (integrations.Integration, string, error) {
+func createExporter(opts component.Options, args component.Arguments) (integrations.Integration, string, error) {
 	a := args.(Arguments)
+	defaultInstanceKey := opts.ID // if cannot resolve instance key, use the component ID
 	return integrations.NewIntegrationWithInstanceKey(opts.Logger, a.Convert(), defaultInstanceKey)
 }
 

internal/component/prometheus/exporter/azure/azure.go

@@ -19,8 +19,9 @@ func init() {
 	})
 }
 
-func createExporter(opts component.Options, args component.Arguments, defaultInstanceKey string) (integrations.Integration, string, error) {
+func createExporter(opts component.Options, args component.Arguments) (integrations.Integration, string, error) {
 	a := args.(Arguments)
+	defaultInstanceKey := opts.ID // if cannot resolve instance key, use the component ID
 	return integrations.NewIntegrationWithInstanceKey(opts.Logger, a.Convert(), defaultInstanceKey)
 }
 

internal/component/prometheus/exporter/blackbox/blackbox.go

@@ -29,8 +29,9 @@ func init() {
 	})
 }
 
-func createExporter(opts component.Options, args component.Arguments, defaultInstanceKey string) (integrations.Integration, string, error) {
+func createExporter(opts component.Options, args component.Arguments) (integrations.Integration, string, error) {
 	a := args.(Arguments)
+	defaultInstanceKey := opts.ID // if cannot resolve instance key, use the component ID
 	return integrations.NewIntegrationWithInstanceKey(opts.Logger, a.Convert(), defaultInstanceKey)
 }