Integrate DNS-SD support for discovering job targets.

config/Makefile

@@ -11,7 +11,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-all: generated
+all: generated/config.pb.go
 
 SUFFIXES:
 

config/config.go

@@ -72,11 +72,17 @@ func (c Config) Validate() error {
 		if _, err := utility.StringToDuration(job.GetScrapeInterval()); err != nil {
 			return fmt.Errorf("Invalid scrape interval for job '%s': %s", job.GetName(), err)
 		}
+		if _, err := utility.StringToDuration(job.GetSdRefreshInterval()); err != nil {
+			return fmt.Errorf("Invalid SD refresh interval for job '%s': %s", job.GetName(), err)
+		}
 		for _, targetGroup := range job.TargetGroup {
 			if err := c.validateLabels(targetGroup.Labels); err != nil {
 				return fmt.Errorf("Invalid labels for job '%s': %s", job.GetName(), err)
 			}
 		}
+		if job.SdName != nil && len(job.TargetGroup) > 0 {
+			return fmt.Errorf("Specified both DNS-SD name and target group for job: %s", job.GetName())
+		}
 	}
 
 	return nil

config/config.proto

@@ -55,8 +55,18 @@ message JobConfig {
 	// How frequently to scrape targets from this job. Overrides the global
 	// default.
 	optional string scrape_interval = 2;
-	// List of labeled target groups for this job.
-	repeated TargetGroup target_group = 3;
+	// The DNS-SD service name pointing to SRV records containing endpoint
+	// information for a job. When this field is provided, no target_group
+	// elements may be set.
+	optional string sd_name = 3;
+  // Discovery refresh period when using DNS-SD to discover targets. Must be a
+  // valid Prometheus duration string in the form "[0-9]+[smhdwy]".
+  optional string sd_refresh_interval = 4 [default = "30s"];
+	// List of labeled target groups for this job. Only legal when DNS-SD isn't
+	// used for a job.
+	repeated TargetGroup target_group = 5;
+	// The HTTP resource path to fetch metrics from on targets.
+	optional string metrics_path = 6 [default = "/metrics.json"];
 }
 
 // The top-level Prometheus configuration.

config/config_test.go

@@ -32,6 +32,8 @@ var configTests = []struct {
 		inputFile: "sample.conf.input",
 	}, {
 		inputFile: "empty.conf.input",
+	}, {
+		inputFile: "sd_targets.conf.input",
 	},
 	{
 		inputFile:   "invalid_proto_format.conf.input",
@@ -53,6 +55,11 @@ var configTests = []struct {
 		shouldFail:  true,
 		errContains: "Invalid label name",
 	},
+	{
+		inputFile:   "mixing_sd_and_manual_targets.conf.input",
+		shouldFail:  true,
+		errContains: "Specified both DNS-SD name and target group",
+	},
 }
 
 func TestConfigs(t *testing.T) {

config/fixtures/mixing_sd_and_manual_targets.conf.input

@@ -0,0 +1,7 @@
+job: <
+  name: "testjob"
+  sd_name: "sd_name"
+  target_group: <
+    target: "http://sampletarget:8080/metrics.json"
+  >
+>

config/fixtures/sd_targets.conf.input

@@ -0,0 +1,4 @@
+job: <
+  name: "testjob"
+  sd_name: "sd_name"
+>

config/generated/config.pb.go

@@ -121,16 +121,22 @@ func (m *TargetGroup) GetLabels() *LabelPairs {
 }
 
 type JobConfig struct {
-	Name             *string        `protobuf:"bytes,1,req,name=name" json:"name,omitempty"`
-	ScrapeInterval   *string        `protobuf:"bytes,2,opt,name=scrape_interval" json:"scrape_interval,omitempty"`
-	TargetGroup      []*TargetGroup `protobuf:"bytes,3,rep,name=target_group" json:"target_group,omitempty"`
-	XXX_unrecognized []byte         `json:"-"`
+	Name              *string        `protobuf:"bytes,1,req,name=name" json:"name,omitempty"`
+	ScrapeInterval    *string        `protobuf:"bytes,2,opt,name=scrape_interval" json:"scrape_interval,omitempty"`
+	SdName            *string        `protobuf:"bytes,3,opt,name=sd_name" json:"sd_name,omitempty"`
+	SdRefreshInterval *string        `protobuf:"bytes,4,opt,name=sd_refresh_interval,def=30s" json:"sd_refresh_interval,omitempty"`
+	TargetGroup       []*TargetGroup `protobuf:"bytes,5,rep,name=target_group" json:"target_group,omitempty"`
+	MetricsPath       *string        `protobuf:"bytes,6,opt,name=metrics_path,def=/metrics.json" json:"metrics_path,omitempty"`
+	XXX_unrecognized  []byte         `json:"-"`
 }
 
 func (m *JobConfig) Reset()         { *m = JobConfig{} }
 func (m *JobConfig) String() string { return proto.CompactTextString(m) }
 func (*JobConfig) ProtoMessage()    {}
 
+const Default_JobConfig_SdRefreshInterval string = "30s"
+const Default_JobConfig_MetricsPath string = "/metrics.json"
+
 func (m *JobConfig) GetName() string {
 	if m != nil && m.Name != nil {
 		return *m.Name
@@ -145,6 +151,20 @@ func (m *JobConfig) GetScrapeInterval() string {
 	return ""
 }
 
+func (m *JobConfig) GetSdName() string {
+	if m != nil && m.SdName != nil {
+		return *m.SdName
+	}
+	return ""
+}
+
+func (m *JobConfig) GetSdRefreshInterval() string {
+	if m != nil && m.SdRefreshInterval != nil {
+		return *m.SdRefreshInterval
+	}
+	return Default_JobConfig_SdRefreshInterval
+}
+
 func (m *JobConfig) GetTargetGroup() []*TargetGroup {
 	if m != nil {
 		return m.TargetGroup
@@ -152,6 +172,13 @@ func (m *JobConfig) GetTargetGroup() []*TargetGroup {
 	return nil
 }
 
+func (m *JobConfig) GetMetricsPath() string {
+	if m != nil && m.MetricsPath != nil {
+		return *m.MetricsPath
+	}
+	return Default_JobConfig_MetricsPath
+}
+
 type PrometheusConfig struct {
 	Global           *GlobalConfig `protobuf:"bytes,1,opt,name=global" json:"global,omitempty"`
 	Job              []*JobConfig  `protobuf:"bytes,2,rep,name=job" json:"job,omitempty"`

retrieval/target_provider.go

@@ -0,0 +1,85 @@
+// Copyright 2013 Prometheus Team
+// 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 retrieval
+
+import (
+	"fmt"
+	"net"
+	"net/url"
+	"time"
+
+	"github.com/prometheus/prometheus/config"
+	"github.com/prometheus/prometheus/model"
+	"github.com/prometheus/prometheus/utility"
+)
+
+// TargetProvider encapsulates retrieving all targets for a job.
+type TargetProvider interface {
+	// Retrieves the current list of targets for this provider.
+	Targets() ([]Target, error)
+}
+
+type sdTargetProvider struct {
+	job config.JobConfig
+
+	targets []Target
+
+	lastRefresh     time.Time
+	refreshInterval time.Duration
+}
+
+// Constructs a new sdTargetProvider for a job.
+func NewSdTargetProvider(job config.JobConfig) *sdTargetProvider {
+	i, err := utility.StringToDuration(job.GetSdRefreshInterval())
+	if err != nil {
+		panic(fmt.Sprintf("illegal refresh duration string %s: %s", job.GetSdRefreshInterval(), err))
+	}
+	return &sdTargetProvider{
+		job:             job,
+		refreshInterval: i,
+	}
+}
+
+func (p *sdTargetProvider) Targets() ([]Target, error) {
+	if time.Since(p.lastRefresh) > p.refreshInterval {
+		return p.targets, nil
+	}
+
+	_, addrs, err := net.LookupSRV("", "", p.job.GetSdName())
+	if err != nil {
+		return nil, err
+	}
+
+	baseLabels := model.LabelSet{
+		model.JobLabel: model.LabelValue(p.job.GetName()),
+	}
+
+	targets := make([]Target, 0, len(addrs))
+	endpoint := &url.URL{
+		Scheme: "http",
+		Path:   p.job.GetMetricsPath(),
+	}
+	for _, addr := range addrs {
+		// Remove the final dot from rooted DNS names to make them look more usual.
+		if addr.Target[len(addr.Target)-1] == '.' {
+			addr.Target = addr.Target[:len(addr.Target)-1]
+		}
+		endpoint.Host = fmt.Sprintf("%s:%d", addr.Target, addr.Port)
+		t := NewTarget(endpoint.String(), time.Second*5, baseLabels)
+		targets = append(targets, t)
+	}
+
+	p.targets = targets
+	return targets, nil
+}

retrieval/targetmanager.go

@@ -57,7 +57,12 @@ func (m *targetManager) TargetPoolForJob(job config.JobConfig) *TargetPool {
 	targetPool, ok := m.poolsByJob[job.GetName()]
 
 	if !ok {
-		targetPool = NewTargetPool(m)
+		var provider TargetProvider = nil
+		if job.SdName != nil {
+			provider = NewSdTargetProvider(job)
+		}
+
+		targetPool = NewTargetPool(m, provider)
 		log.Printf("Pool for job %s does not exist; creating and starting...", job.GetName())
 
 		interval := job.ScrapeInterval()
@@ -86,6 +91,11 @@ func (m targetManager) Remove(t Target) {
 
 func (m *targetManager) AddTargetsFromConfig(config config.Config) {
 	for _, job := range config.Jobs() {
+		if job.SdName != nil {
+			m.TargetPoolForJob(job)
+			continue
+		}
+
 		for _, targetGroup := range job.TargetGroup {
 			baseLabels := model.LabelSet{
 				model.JobLabel: model.LabelValue(job.GetName()),

retrieval/targetpool.go

@@ -37,13 +37,16 @@ type TargetPool struct {
 	targets             targets
 	addTargetQueue      chan Target
 	replaceTargetsQueue chan targets
+
+	targetProvider TargetProvider
 }
 
-func NewTargetPool(m TargetManager) *TargetPool {
+func NewTargetPool(m TargetManager, p TargetProvider) *TargetPool {
 	return &TargetPool{
 		manager:             m,
 		addTargetQueue:      make(chan Target, targetAddQueueSize),
 		replaceTargetsQueue: make(chan targets, targetReplaceQueueSize),
+		targetProvider:      p,
 	}
 }
 
@@ -121,6 +124,15 @@ func (p *TargetPool) runSingle(earliest time.Time, results chan format.Result, t
 }
 
 func (p *TargetPool) runIteration(results chan format.Result, interval time.Duration) {
+	if p.targetProvider != nil {
+		targets, err := p.targetProvider.Targets()
+		if err != nil {
+			log.Printf("Error looking up targets: %s", err)
+			return
+		}
+		p.ReplaceTargets(targets)
+	}
+
 	p.RLock()
 	defer p.RUnlock()