converters: Default with localhost in static targets when none provid…

…ed (#5546)

* promtail: Default with localhost in static targets in converter

* Add tests and changelog

* prettify

* feedback

CHANGELOG.md

@@ -58,6 +58,9 @@ Main (unreleased)
 
 - Fixed an issue where native histogram time series were being dropped silently.  (@krajorama)
 
+- Fix an issue with static mode and `promtail` converters, where static targets 
+  did not correctly default to `localhost` when not provided. (@thampiotr)
+
 ### Enhancements
 
 - The `loki.write` WAL now has snappy compression enabled by default. (@thepalbi)

converter/internal/promtailconvert/internal/build/service_discovery.go

@@ -1,13 +1,16 @@
 package build
 
 import (
+	"fmt"
+
 	"github.com/grafana/agent/component/discovery"
 	"github.com/grafana/agent/converter/diag"
 	"github.com/grafana/agent/converter/internal/common"
 	"github.com/grafana/agent/converter/internal/prometheusconvert"
 	"github.com/grafana/agent/converter/internal/prometheusconvert/build"
 
 	"github.com/grafana/loki/clients/pkg/promtail/scrapeconfig"
+	"github.com/prometheus/common/model"
 	prom_discover "github.com/prometheus/prometheus/discovery"
 )
 
@@ -107,6 +110,16 @@ func toDiscoveryConfig(cfg *scrapeconfig.Config) prom_discover.Configs {
 	}
 
 	if len(cfg.ServiceDiscoveryConfig.StaticConfigs) != 0 {
+		// Add source and default 'localhost' target to match Promtail's behaviour.
+		// See https://github.com/grafana/loki/blob/4a564456861c0ab7441b815aa49a7c0f22a05f4c/clients/pkg/promtail/targets/file/filetargetmanager.go#L102
+		for i, targetGroup := range cfg.ServiceDiscoveryConfig.StaticConfigs {
+			targetGroup.Source = fmt.Sprintf("%d", i)
+			if len(targetGroup.Targets) == 0 {
+				targetGroup.Targets = []model.LabelSet{
+					{model.AddressLabel: "localhost"},
+				}
+			}
+		}
 		sdConfigs = append(sdConfigs, cfg.ServiceDiscoveryConfig.StaticConfigs)
 	}
 

converter/internal/promtailconvert/testdata/static_pipeline_example.river

@@ -32,6 +32,12 @@ discovery.relabel "example" {
 			__path__exclude__ = "/shelf/books/star_wars*",
 			category          = "sf",
 			quality           = "high",
+		}, {
+			__address__ = "localhost",
+			__path__    = "/var/log/this_is_used.log",
+			category    = "important",
+		}, {
+			__address__ = "localhost",
 		}],
 	)
 

converter/internal/promtailconvert/testdata/static_pipeline_example.yaml

@@ -39,8 +39,8 @@ scrape_configs:
           category: sf
           quality: high
       - labels:
-          __path__: /var/log/this_is_not_used.log
-          category: superfluous
+          __path__: /var/log/this_is_used.log
+          category: important
       - labels: { }
     # Include k8s config to demonstrate how other discovery features differ from static_configs
     kubernetes_sd_configs: