From d7afefd0ffdbfcc2ee39675851245f5d588b23f8 Mon Sep 17 00:00:00 2001
From: JBD <jbd@amazon.com>
Date: Fri, 9 Jul 2021 14:44:16 -0700
Subject: [PATCH 1/2] Validate the Prometheus config

Validate against nil configuration and configuration with no scrape_configs.

Fixes #2705.
---
 receiver/prometheusreceiver/config.go  | 19 +++++++++----------
 receiver/prometheusreceiver/factory.go |  4 ++--
 2 files changed, 11 insertions(+), 12 deletions(-)

diff --git a/receiver/prometheusreceiver/config.go b/receiver/prometheusreceiver/config.go
index f5e7d445f1a..1f6c683ac32 100644
--- a/receiver/prometheusreceiver/config.go
+++ b/receiver/prometheusreceiver/config.go
@@ -51,16 +51,15 @@ var _ config.CustomUnmarshable = (*Config)(nil)
 
 // Validate checks the receiver configuration is valid
 func (cfg *Config) Validate() error {
-	if cfg.PrometheusConfig != nil {
-		if len(cfg.PrometheusConfig.ScrapeConfigs) == 0 {
-			return errNilScrapeConfig
-		}
-		for _, sc := range cfg.PrometheusConfig.ScrapeConfigs {
-			for _, rc := range sc.MetricRelabelConfigs {
-				if rc.TargetLabel == "__name__" {
-					// TODO(#2297): Remove validation after renaming is fixed
-					return fmt.Errorf("error validating scrapeconfig for job %v: %w", sc.JobName, errRenamingDisallowed)
-				}
+	if cfg.PrometheusConfig == nil || len(cfg.PrometheusConfig.ScrapeConfigs) == 0 {
+		return errInvalidPrometheusConfig
+	}
+
+	for _, sc := range cfg.PrometheusConfig.ScrapeConfigs {
+		for _, rc := range sc.MetricRelabelConfigs {
+			if rc.TargetLabel == "__name__" {
+				// TODO(#2297): Remove validation after renaming is fixed
+				return fmt.Errorf("error validating scrapeconfig for job %v: %w", sc.JobName, errRenamingDisallowed)
 			}
 		}
 	}
diff --git a/receiver/prometheusreceiver/factory.go b/receiver/prometheusreceiver/factory.go
index 98f5e9b68aa..daf8225d2f4 100644
--- a/receiver/prometheusreceiver/factory.go
+++ b/receiver/prometheusreceiver/factory.go
@@ -33,8 +33,8 @@ const (
 )
 
 var (
-	errNilScrapeConfig    = errors.New("expecting a non-nil ScrapeConfig")
-	errRenamingDisallowed = errors.New("metric renaming using metric_relabel_configs is disallowed")
+	errInvalidPrometheusConfig = errors.New("expecting a non-nil Prometheus config with a valid scrape_configs section")
+	errRenamingDisallowed      = errors.New("metric renaming using metric_relabel_configs is disallowed")
 )
 
 // NewFactory creates a new Prometheus receiver factory.

From ba1a200fc3d951ef915353f5115813232d60c017 Mon Sep 17 00:00:00 2001
From: JBD <jbd@amazon.com>
Date: Mon, 12 Jul 2021 11:14:22 -0700
Subject: [PATCH 2/2] Allow initialization of recievers without any
 configuration

---
 receiver/prometheusreceiver/config.go  | 11 ++++++++---
 receiver/prometheusreceiver/factory.go |  5 +----
 2 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/receiver/prometheusreceiver/config.go b/receiver/prometheusreceiver/config.go
index 1f6c683ac32..af310545393 100644
--- a/receiver/prometheusreceiver/config.go
+++ b/receiver/prometheusreceiver/config.go
@@ -15,6 +15,7 @@
 package prometheusreceiver
 
 import (
+	"errors"
 	"fmt"
 	"time"
 
@@ -49,10 +50,13 @@ type Config struct {
 var _ config.Receiver = (*Config)(nil)
 var _ config.CustomUnmarshable = (*Config)(nil)
 
-// Validate checks the receiver configuration is valid
+// Validate checks the receiver configuration is valid.
 func (cfg *Config) Validate() error {
-	if cfg.PrometheusConfig == nil || len(cfg.PrometheusConfig.ScrapeConfigs) == 0 {
-		return errInvalidPrometheusConfig
+	if cfg.PrometheusConfig == nil {
+		return nil // noop receiver
+	}
+	if len(cfg.PrometheusConfig.ScrapeConfigs) == 0 {
+		return errors.New("no Prometheus scrape_configs")
 	}
 
 	for _, sc := range cfg.PrometheusConfig.ScrapeConfigs {
@@ -93,5 +97,6 @@ func (cfg *Config) Unmarshal(componentParser *configparser.Parser) error {
 	if err != nil {
 		return fmt.Errorf("prometheus receiver failed to unmarshal yaml to prometheus config: %s", err)
 	}
+
 	return nil
 }
diff --git a/receiver/prometheusreceiver/factory.go b/receiver/prometheusreceiver/factory.go
index daf8225d2f4..74e57098294 100644
--- a/receiver/prometheusreceiver/factory.go
+++ b/receiver/prometheusreceiver/factory.go
@@ -32,10 +32,7 @@ const (
 	typeStr = "prometheus"
 )
 
-var (
-	errInvalidPrometheusConfig = errors.New("expecting a non-nil Prometheus config with a valid scrape_configs section")
-	errRenamingDisallowed      = errors.New("metric renaming using metric_relabel_configs is disallowed")
-)
+var errRenamingDisallowed = errors.New("metric renaming using metric_relabel_configs is disallowed")
 
 // NewFactory creates a new Prometheus receiver factory.
 func NewFactory() component.ReceiverFactory {