From 8850660790ac5e615d13647752fbb49b4b50ea37 Mon Sep 17 00:00:00 2001
From: Piotr <17101802+thampiotr@users.noreply.github.com>
Date: Fri, 20 Oct 2023 15:51:18 +0100
Subject: [PATCH] converters: Default with localhost in static targets when
 none provided (#5546)

* promtail: Default with localhost in static targets in converter

* Add tests and changelog

* prettify

* feedback
---
 CHANGELOG.md                                        |  3 +++
 .../internal/build/service_discovery.go             | 13 +++++++++++++
 .../testdata/static_pipeline_example.river          |  6 ++++++
 .../testdata/static_pipeline_example.yaml           |  4 ++--
 4 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index b3b26e1f86f9..52c1a6db8bfb 100644
--- a/CHANGELOG.md
+++ b/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)
diff --git a/converter/internal/promtailconvert/internal/build/service_discovery.go b/converter/internal/promtailconvert/internal/build/service_discovery.go
index 37489bc66c59..6219bc2b121d 100644
--- a/converter/internal/promtailconvert/internal/build/service_discovery.go
+++ b/converter/internal/promtailconvert/internal/build/service_discovery.go
@@ -1,6 +1,8 @@
 package build
 
 import (
+	"fmt"
+
 	"github.com/grafana/agent/component/discovery"
 	"github.com/grafana/agent/converter/diag"
 	"github.com/grafana/agent/converter/internal/common"
@@ -8,6 +10,7 @@ import (
 	"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)
 	}
 
diff --git a/converter/internal/promtailconvert/testdata/static_pipeline_example.river b/converter/internal/promtailconvert/testdata/static_pipeline_example.river
index d105b315036a..3b7e4b20b436 100644
--- a/converter/internal/promtailconvert/testdata/static_pipeline_example.river
+++ b/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",
 		}],
 	)
 
diff --git a/converter/internal/promtailconvert/testdata/static_pipeline_example.yaml b/converter/internal/promtailconvert/testdata/static_pipeline_example.yaml
index 2608cfb8825e..80239d45eada 100644
--- a/converter/internal/promtailconvert/testdata/static_pipeline_example.yaml
+++ b/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: