[receiver/prometheus] syncTargetAllocator now detects regex changes in relabel config

.chloggen/fix_promTAHashComputation.yaml

@@ -0,0 +1,6 @@
+change_type: 'bug_fix'
+component: 'prometheusreceiver'
+note: Fix hash computation to include non exported fields like regex in scrape configuration for TargetAllocator
+issues: [29313]
+subtext:
+change_logs: []

cmd/otelcontribcol/go.mod

@@ -598,7 +598,6 @@ require (
 	github.com/mitchellh/go-homedir v1.1.0 // indirect
 	github.com/mitchellh/go-ps v1.0.0 // indirect
 	github.com/mitchellh/hashstructure v1.1.0 // indirect
-	github.com/mitchellh/hashstructure/v2 v2.0.2 // indirect
 	github.com/mitchellh/mapstructure v1.5.1-0.20231216201459-8508981c8b6c // indirect
 	github.com/mitchellh/reflectwalk v1.0.2 // indirect
 	github.com/moby/docker-image-spec v1.3.1 // indirect

cmd/oteltestbedcol/go.mod

@@ -169,7 +169,6 @@ require (
 	github.com/miekg/dns v1.1.59 // indirect
 	github.com/mitchellh/copystructure v1.2.0 // indirect
 	github.com/mitchellh/go-homedir v1.1.0 // indirect
-	github.com/mitchellh/hashstructure/v2 v2.0.2 // indirect
 	github.com/mitchellh/mapstructure v1.5.1-0.20231216201459-8508981c8b6c // indirect
 	github.com/mitchellh/reflectwalk v1.0.2 // indirect
 	github.com/moby/docker-image-spec v1.3.1 // indirect

exporter/datadogexporter/go.mod

@@ -244,7 +244,6 @@ require (
 	github.com/miekg/dns v1.1.59 // indirect
 	github.com/mitchellh/copystructure v1.2.0 // indirect
 	github.com/mitchellh/go-homedir v1.1.0 // indirect
-	github.com/mitchellh/hashstructure/v2 v2.0.2 // indirect
 	github.com/mitchellh/mapstructure v1.5.1-0.20231216201459-8508981c8b6c // indirect
 	github.com/mitchellh/reflectwalk v1.0.2 // indirect
 	github.com/moby/docker-image-spec v1.3.1 // indirect

exporter/prometheusexporter/go.mod

@@ -118,7 +118,6 @@ require (
 	github.com/miekg/dns v1.1.59 // indirect
 	github.com/mitchellh/copystructure v1.2.0 // indirect
 	github.com/mitchellh/go-homedir v1.1.0 // indirect
-	github.com/mitchellh/hashstructure/v2 v2.0.2 // indirect
 	github.com/mitchellh/mapstructure v1.5.1-0.20231216201459-8508981c8b6c // indirect
 	github.com/mitchellh/reflectwalk v1.0.2 // indirect
 	github.com/moby/docker-image-spec v1.3.1 // indirect

receiver/prometheusreceiver/go.mod

@@ -6,7 +6,6 @@ require (
 	github.com/go-kit/log v0.2.1
 	github.com/gogo/protobuf v1.3.2
 	github.com/golang/snappy v0.0.4
-	github.com/mitchellh/hashstructure/v2 v2.0.2
 	github.com/open-telemetry/opentelemetry-collector-contrib/exporter/prometheusremotewriteexporter v0.104.0
 	github.com/open-telemetry/opentelemetry-collector-contrib/internal/common v0.104.0
 	github.com/open-telemetry/opentelemetry-collector-contrib/pkg/pdatautil v0.104.0

receiver/prometheusreceiver/metrics_receiver.go

@@ -8,18 +8,19 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"hash/fnv"
 	"io"
 	"net/http"
 	"net/url"
 	"os"
 	"reflect"
 	"regexp"
+	"sort"
 	"sync"
 	"time"
 	"unsafe"
 
 	"github.com/go-kit/log"
-	"github.com/mitchellh/hashstructure/v2"
 	"github.com/prometheus/client_golang/prometheus"
 	commonconfig "github.com/prometheus/common/config"
 	"github.com/prometheus/common/model"
@@ -145,6 +146,33 @@ func (r *pReceiver) startTargetAllocator(allocConf *TargetAllocator, baseCfg *Pr
 	return nil
 }
 
+// Calculate a hash for a scrape config map.
+// This is done by marshaling to YAML because it's the most straightforward and doesn't run into problems with unexported fields.
+func getScrapeConfigHash(jobToScrapeConfig map[string]*config.ScrapeConfig) (uint64, error) {
+	var err error
+	hash := fnv.New64()
+	yamlEncoder := yaml.NewEncoder(hash)
+
+	jobKeys := make([]string, 0, len(jobToScrapeConfig))
+	for jobName := range jobToScrapeConfig {
+		jobKeys = append(jobKeys, jobName)
+	}
+	sort.Strings(jobKeys)
+
+	for _, jobName := range jobKeys {
+		_, err = hash.Write([]byte(jobName))
+		if err != nil {
+			return 0, err
+		}
+		err = yamlEncoder.Encode(jobToScrapeConfig[jobName])
+		if err != nil {
+			return 0, err
+		}
+	}
+	yamlEncoder.Close()
+	return hash.Sum64(), err
+}
+
 // syncTargetAllocator request jobs from targetAllocator and update underlying receiver, if the response does not match the provided compareHash.
 // baseDiscoveryCfg can be used to provide additional ScrapeConfigs which will be added to the retrieved jobs.
 func (r *pReceiver) syncTargetAllocator(compareHash uint64, allocConf *TargetAllocator, baseCfg *PromConfig) (uint64, error) {
@@ -155,7 +183,7 @@ func (r *pReceiver) syncTargetAllocator(compareHash uint64, allocConf *TargetAll
 		return 0, err
 	}
 
-	hash, err := hashstructure.Hash(scrapeConfigsResponse, hashstructure.FormatV2, nil)
+	hash, err := getScrapeConfigHash(scrapeConfigsResponse)
 	if err != nil {
 		r.settings.Logger.Error("Failed to hash job list", zap.Error(err))
 		return 0, err