WIP: Optimise Prometheus targets handling

internal/component/beyla/ebpf/beyla_linux.go

@@ -273,17 +273,17 @@ func (c *Component) Update(args component.Arguments) error {
 func (c *Component) baseTarget() (discovery.Target, error) {
 	data, err := c.opts.GetServiceData(http_service.ServiceName)
 	if err != nil {
-		return nil, fmt.Errorf("failed to get HTTP information: %w", err)
+		return discovery.EmptyTarget, fmt.Errorf("failed to get HTTP information: %w", err)
 	}
 	httpData := data.(http_service.Data)
 
-	return discovery.Target{
+	return discovery.NewTargetFromMap(map[string]string{
 		model.AddressLabel:     httpData.MemoryListenAddr,
 		model.SchemeLabel:      "http",
 		model.MetricsPathLabel: path.Join(httpData.HTTPPathForComponent(c.opts.ID), "metrics"),
 		"instance":             defaultInstance(),
 		"job":                  "beyla",
-	}, nil
+	}), nil
 }
 
 func (c *Component) reportUnhealthy(err error) {

internal/component/common/relabel/label_builder.go

@@ -0,0 +1,9 @@
+package relabel
+
+// LabelBuilder is an interface that can be used to change labels with relabel logic.
+type LabelBuilder interface {
+	Get(label string) string
+	Range(f func(label string, value string))
+	Set(label string, val string)
+	Del(ns ...string)
+}

internal/component/common/relabel/relabel.go

@@ -1,8 +1,26 @@
+// NOTE: this is adapted from Prometheus codebase to work correctly with Alloy types.
+
+// Copyright 2015 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
 package relabel
 
 import (
+	"crypto/md5"
+	"encoding/binary"
 	"fmt"
 	"reflect"
+	"strings"
 
 	"github.com/grafana/regexp"
 	"github.com/prometheus/common/model"
@@ -149,7 +167,13 @@ func (rc *Config) Validate() error {
 	if (rc.Action == Replace || rc.Action == HashMod || rc.Action == Lowercase || rc.Action == Uppercase || rc.Action == KeepEqual || rc.Action == DropEqual) && rc.TargetLabel == "" {
 		return fmt.Errorf("relabel configuration for %s action requires 'target_label' value", rc.Action)
 	}
-	if (rc.Action == Replace || rc.Action == Lowercase || rc.Action == Uppercase || rc.Action == KeepEqual || rc.Action == DropEqual) && !relabelTarget.MatchString(rc.TargetLabel) {
+	if rc.Action == Replace && !strings.Contains(rc.TargetLabel, "$") && !model.LabelName(rc.TargetLabel).IsValid() {
+		return fmt.Errorf("%q is invalid 'target_label' for %s action", rc.TargetLabel, rc.Action)
+	}
+	if rc.Action == Replace && strings.Contains(rc.TargetLabel, "$") && !relabelTarget.MatchString(rc.TargetLabel) {
+		return fmt.Errorf("%q is invalid 'target_label' for %s action", rc.TargetLabel, rc.Action)
+	}
+	if (rc.Action == Lowercase || rc.Action == Uppercase || rc.Action == KeepEqual || rc.Action == DropEqual) && !model.LabelName(rc.TargetLabel).IsValid() {
 		return fmt.Errorf("%q is invalid 'target_label' for %s action", rc.TargetLabel, rc.Action)
 	}
 	if (rc.Action == Lowercase || rc.Action == Uppercase || rc.Action == KeepEqual || rc.Action == DropEqual) && rc.Replacement != DefaultRelabelConfig.Replacement {
@@ -186,6 +210,97 @@ func (rc *Config) Validate() error {
 	return nil
 }
 
+// ProcessBuilder is like Process, but the caller passes a labels.Builder
+// containing the initial set of labels, which is mutated by the rules.
+func ProcessBuilder(lb LabelBuilder, cfgs ...*Config) (keep bool) {
+	for _, cfg := range cfgs {
+		keep = doRelabel(cfg, lb)
+		if !keep {
+			return false
+		}
+	}
+	return true
+}
+
+func doRelabel(cfg *Config, lb LabelBuilder) (keep bool) {
+	var va [16]string
+	values := va[:0]
+	if len(cfg.SourceLabels) > cap(values) {
+		values = make([]string, 0, len(cfg.SourceLabels))
+	}
+	for _, ln := range cfg.SourceLabels {
+		values = append(values, lb.Get(string(ln)))
+	}
+	val := strings.Join(values, cfg.Separator)
+
+	switch cfg.Action {
+	case Drop:
+		if cfg.Regex.MatchString(val) {
+			return false
+		}
+	case Keep:
+		if !cfg.Regex.MatchString(val) {
+			return false
+		}
+	case DropEqual:
+		if lb.Get(cfg.TargetLabel) == val {
+			return false
+		}
+	case KeepEqual:
+		if lb.Get(cfg.TargetLabel) != val {
+			return false
+		}
+	case Replace:
+		indexes := cfg.Regex.FindStringSubmatchIndex(val)
+		// If there is no match no replacement must take place.
+		if indexes == nil {
+			break
+		}
+		target := model.LabelName(cfg.Regex.ExpandString([]byte{}, cfg.TargetLabel, val, indexes))
+		if !target.IsValid() {
+			break
+		}
+		res := cfg.Regex.ExpandString([]byte{}, cfg.Replacement, val, indexes)
+		if len(res) == 0 {
+			lb.Del(string(target))
+			break
+		}
+		lb.Set(string(target), string(res))
+	case Lowercase:
+		lb.Set(cfg.TargetLabel, strings.ToLower(val))
+	case Uppercase:
+		lb.Set(cfg.TargetLabel, strings.ToUpper(val))
+	case HashMod:
+		hash := md5.Sum([]byte(val))
+		// Use only the last 8 bytes of the hash to give the same result as earlier versions of this code.
+		mod := binary.BigEndian.Uint64(hash[8:]) % cfg.Modulus
+		lb.Set(cfg.TargetLabel, fmt.Sprintf("%d", mod))
+	case LabelMap:
+		lb.Range(func(name, value string) {
+			if cfg.Regex.MatchString(name) {
+				res := cfg.Regex.ReplaceAllString(name, cfg.Replacement)
+				lb.Set(res, value)
+			}
+		})
+	case LabelDrop:
+		lb.Range(func(name, value string) {
+			if cfg.Regex.MatchString(name) {
+				lb.Del(name)
+			}
+		})
+	case LabelKeep:
+		lb.Range(func(name, value string) {
+			if !cfg.Regex.MatchString(name) {
+				lb.Del(name)
+			}
+		})
+	default:
+		panic(fmt.Errorf("relabel: unknown relabel action type %q", cfg.Action))
+	}
+
+	return true
+}
+
 // ComponentToPromRelabelConfigs bridges the Component-based configuration of
 // relabeling steps to the Prometheus implementation.
 func ComponentToPromRelabelConfigs(rcs []*Config) []*relabel.Config {