diff --git a/retrieval/discovery/azure.go b/discovery/azure/azure.go
similarity index 94%
rename from retrieval/discovery/azure.go
rename to discovery/azure/azure.go
index cec54af86e..c0f354230c 100644
--- a/retrieval/discovery/azure.go
+++ b/discovery/azure/azure.go
@@ -11,7 +11,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package discovery
+package azure
 
 import (
 	"fmt"
@@ -45,15 +45,13 @@ const (
 var (
 	azureSDRefreshFailuresCount = prometheus.NewCounter(
 		prometheus.CounterOpts{
-			Namespace: namespace,
-			Name:      "sd_azure_refresh_failures_total",
-			Help:      "Number of Azure-SD refresh failures.",
+			Name: "prometheus_sd_azure_refresh_failures_total",
+			Help: "Number of Azure-SD refresh failures.",
 		})
 	azureSDRefreshDuration = prometheus.NewSummary(
 		prometheus.SummaryOpts{
-			Namespace: namespace,
-			Name:      "sd_azure_refresh_duration_seconds",
-			Help:      "The duration of a Azure-SD refresh in seconds.",
+			Name: "prometheus_sd_azure_refresh_duration_seconds",
+			Help: "The duration of a Azure-SD refresh in seconds.",
 		})
 )
 
@@ -70,8 +68,8 @@ type AzureDiscovery struct {
 	port     int
 }
 
-// NewAzureDiscovery returns a new AzureDiscovery which periodically refreshes its targets.
-func NewAzureDiscovery(cfg *config.AzureSDConfig) *AzureDiscovery {
+// NewDiscovery returns a new AzureDiscovery which periodically refreshes its targets.
+func NewDiscovery(cfg *config.AzureSDConfig) *AzureDiscovery {
 	return &AzureDiscovery{
 		cfg:      cfg,
 		interval: time.Duration(cfg.RefreshInterval),
diff --git a/retrieval/discovery/consul/consul.go b/discovery/consul/consul.go
similarity index 100%
rename from retrieval/discovery/consul/consul.go
rename to discovery/consul/consul.go
diff --git a/discovery/discovery.go b/discovery/discovery.go
new file mode 100644
index 0000000000..628ebb71f2
--- /dev/null
+++ b/discovery/discovery.go
@@ -0,0 +1,302 @@
+// Copyright 2016 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 discovery
+
+import (
+	"fmt"
+	"sync"
+	"time"
+
+	"github.com/prometheus/common/log"
+	"github.com/prometheus/prometheus/config"
+	"github.com/prometheus/prometheus/discovery/azure"
+	"github.com/prometheus/prometheus/discovery/consul"
+	"github.com/prometheus/prometheus/discovery/dns"
+	"github.com/prometheus/prometheus/discovery/ec2"
+	"github.com/prometheus/prometheus/discovery/file"
+	"github.com/prometheus/prometheus/discovery/gce"
+	"github.com/prometheus/prometheus/discovery/kubernetes"
+	"github.com/prometheus/prometheus/discovery/marathon"
+	"github.com/prometheus/prometheus/discovery/zookeeper"
+	"golang.org/x/net/context"
+)
+
+// A TargetProvider provides information about target groups. It maintains a set
+// of sources from which TargetGroups can originate. Whenever a target provider
+// detects a potential change, it sends the TargetGroup through its provided channel.
+//
+// The TargetProvider does not have to guarantee that an actual change happened.
+// It does guarantee that it sends the new TargetGroup whenever a change happens.
+//
+// TargetProviders should initially send a full set of all discoverable TargetGroups.
+type TargetProvider interface {
+	// Run hands a channel to the target provider through which it can send
+	// updated target groups.
+	// Must returns if the context gets canceled. It should not close the update
+	// channel on returning.
+	Run(ctx context.Context, up chan<- []*config.TargetGroup)
+}
+
+// ProvidersFromConfig returns all TargetProviders configured in cfg.
+func ProvidersFromConfig(cfg *config.ScrapeConfig) map[string]TargetProvider {
+	providers := map[string]TargetProvider{}
+
+	app := func(mech string, i int, tp TargetProvider) {
+		providers[fmt.Sprintf("%s/%d", mech, i)] = tp
+	}
+
+	for i, c := range cfg.DNSSDConfigs {
+		app("dns", i, dns.NewDiscovery(c))
+	}
+	for i, c := range cfg.FileSDConfigs {
+		app("file", i, file.NewDiscovery(c))
+	}
+	for i, c := range cfg.ConsulSDConfigs {
+		k, err := consul.NewDiscovery(c)
+		if err != nil {
+			log.Errorf("Cannot create Consul discovery: %s", err)
+			continue
+		}
+		app("consul", i, k)
+	}
+	for i, c := range cfg.MarathonSDConfigs {
+		m, err := marathon.NewDiscovery(c)
+		if err != nil {
+			log.Errorf("Cannot create Marathon discovery: %s", err)
+			continue
+		}
+		app("marathon", i, m)
+	}
+	for i, c := range cfg.KubernetesSDConfigs {
+		k, err := kubernetes.New(log.Base(), c)
+		if err != nil {
+			log.Errorf("Cannot create Kubernetes discovery: %s", err)
+			continue
+		}
+		app("kubernetes", i, k)
+	}
+	for i, c := range cfg.ServersetSDConfigs {
+		app("serverset", i, zookeeper.NewServersetDiscovery(c))
+	}
+	for i, c := range cfg.NerveSDConfigs {
+		app("nerve", i, zookeeper.NewNerveDiscovery(c))
+	}
+	for i, c := range cfg.EC2SDConfigs {
+		app("ec2", i, ec2.NewDiscovery(c))
+	}
+	for i, c := range cfg.GCESDConfigs {
+		gced, err := gce.NewDiscovery(c)
+		if err != nil {
+			log.Errorf("Cannot initialize GCE discovery: %s", err)
+			continue
+		}
+		app("gce", i, gced)
+	}
+	for i, c := range cfg.AzureSDConfigs {
+		app("azure", i, azure.NewDiscovery(c))
+	}
+	if len(cfg.StaticConfigs) > 0 {
+		app("static", 0, NewStaticProvider(cfg.StaticConfigs))
+	}
+
+	return providers
+}
+
+// StaticProvider holds a list of target groups that never change.
+type StaticProvider struct {
+	TargetGroups []*config.TargetGroup
+}
+
+// NewStaticProvider returns a StaticProvider configured with the given
+// target groups.
+func NewStaticProvider(groups []*config.TargetGroup) *StaticProvider {
+	for i, tg := range groups {
+		tg.Source = fmt.Sprintf("%d", i)
+	}
+	return &StaticProvider{groups}
+}
+
+// Run implements the TargetProvider interface.
+func (sd *StaticProvider) Run(ctx context.Context, ch chan<- []*config.TargetGroup) {
+	// We still have to consider that the consumer exits right away in which case
+	// the context will be canceled.
+	select {
+	case ch <- sd.TargetGroups:
+	case <-ctx.Done():
+	}
+	close(ch)
+}
+
+// TargetSet handles multiple TargetProviders and sends a full overview of their
+// discovered TargetGroups to a Syncer.
+type TargetSet struct {
+	mtx sync.RWMutex
+	// Sets of targets by a source string that is unique across target providers.
+	tgroups map[string]*config.TargetGroup
+
+	syncer Syncer
+
+	syncCh          chan struct{}
+	providerCh      chan map[string]TargetProvider
+	cancelProviders func()
+}
+
+// Syncer receives updates complete sets of TargetGroups.
+type Syncer interface {
+	Sync([]*config.TargetGroup)
+}
+
+// NewTargetSet returns a new target sending TargetGroups to the Syncer.
+func NewTargetSet(s Syncer) *TargetSet {
+	return &TargetSet{
+		syncCh:     make(chan struct{}, 1),
+		providerCh: make(chan map[string]TargetProvider),
+		syncer:     s,
+	}
+}
+
+// Run starts the processing of target providers and their updates.
+// It blocks until the context gets canceled.
+func (ts *TargetSet) Run(ctx context.Context) {
+Loop:
+	for {
+		// Throttle syncing to once per five seconds.
+		select {
+		case <-ctx.Done():
+			break Loop
+		case p := <-ts.providerCh:
+			ts.updateProviders(ctx, p)
+		case <-time.After(5 * time.Second):
+		}
+
+		select {
+		case <-ctx.Done():
+			break Loop
+		case <-ts.syncCh:
+			ts.sync()
+		case p := <-ts.providerCh:
+			ts.updateProviders(ctx, p)
+		}
+	}
+}
+
+func (ts *TargetSet) sync() {
+	ts.mtx.RLock()
+	var all []*config.TargetGroup
+	for _, tg := range ts.tgroups {
+		all = append(all, tg)
+	}
+	ts.mtx.RUnlock()
+
+	ts.syncer.Sync(all)
+}
+
+// UpdateProviders sets new target providers for the target set.
+func (ts *TargetSet) UpdateProviders(p map[string]TargetProvider) {
+	ts.providerCh <- p
+}
+
+func (ts *TargetSet) updateProviders(ctx context.Context, providers map[string]TargetProvider) {
+	// Lock for the entire time. This may mean up to 5 seconds until the full initial set
+	// is retrieved and applied.
+	// We could release earlier with some tweaks, but this is easier to reason about.
+	ts.mtx.Lock()
+	defer ts.mtx.Unlock()
+
+	// Stop all previous target providers of the target set.
+	if ts.cancelProviders != nil {
+		ts.cancelProviders()
+	}
+	ctx, ts.cancelProviders = context.WithCancel(ctx)
+
+	var wg sync.WaitGroup
+	// (Re-)create a fresh tgroups map to not keep stale targets around. We
+	// will retrieve all targets below anyway, so cleaning up everything is
+	// safe and doesn't inflict any additional cost.
+	ts.tgroups = map[string]*config.TargetGroup{}
+
+	for name, prov := range providers {
+		wg.Add(1)
+
+		updates := make(chan []*config.TargetGroup)
+		go prov.Run(ctx, updates)
+
+		go func(name string, prov TargetProvider) {
+			select {
+			case <-ctx.Done():
+			case initial, ok := <-updates:
+				// Handle the case that a target provider exits and closes the channel
+				// before the context is done.
+				if !ok {
+					break
+				}
+				// First set of all targets the provider knows.
+				for _, tgroup := range initial {
+					ts.setTargetGroup(name, tgroup)
+				}
+			case <-time.After(5 * time.Second):
+				// Initial set didn't arrive. Act as if it was empty
+				// and wait for updates later on.
+			}
+			wg.Done()
+
+			// Start listening for further updates.
+			for {
+				select {
+				case <-ctx.Done():
+					return
+				case tgs, ok := <-updates:
+					// Handle the case that a target provider exits and closes the channel
+					// before the context is done.
+					if !ok {
+						return
+					}
+					for _, tg := range tgs {
+						ts.update(name, tg)
+					}
+				}
+			}
+		}(name, prov)
+	}
+
+	// We wait for a full initial set of target groups before releasing the mutex
+	// to ensure the initial sync is complete and there are no races with subsequent updates.
+	wg.Wait()
+	// Just signal that there are initial sets to sync now. Actual syncing must only
+	// happen in the runScraping loop.
+	select {
+	case ts.syncCh <- struct{}{}:
+	default:
+	}
+}
+
+// update handles a target group update from a target provider identified by the name.
+func (ts *TargetSet) update(name string, tgroup *config.TargetGroup) {
+	ts.mtx.Lock()
+	defer ts.mtx.Unlock()
+
+	ts.setTargetGroup(name, tgroup)
+
+	select {
+	case ts.syncCh <- struct{}{}:
+	default:
+	}
+}
+
+func (ts *TargetSet) setTargetGroup(name string, tg *config.TargetGroup) {
+	if tg == nil {
+		return
+	}
+	ts.tgroups[name+"/"+tg.Source] = tg
+}
diff --git a/discovery/discovery_test.go b/discovery/discovery_test.go
new file mode 100644
index 0000000000..edb3480ac1
--- /dev/null
+++ b/discovery/discovery_test.go
@@ -0,0 +1,87 @@
+// Copyright 2016 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 discovery
+
+import (
+	"testing"
+
+	"github.com/prometheus/prometheus/config"
+	"golang.org/x/net/context"
+	yaml "gopkg.in/yaml.v2"
+)
+
+func TestTargetSetRecreatesTargetGroupsEveryRun(t *testing.T) {
+
+	verifyPresence := func(tgroups map[string]*config.TargetGroup, name string, present bool) {
+		if _, ok := tgroups[name]; ok != present {
+			msg := ""
+			if !present {
+				msg = "not "
+			}
+			t.Fatalf("'%s' should %sbe present in TargetSet.tgroups: %s", name, msg, tgroups)
+		}
+	}
+
+	scrapeConfig := &config.ScrapeConfig{}
+
+	sOne := `
+job_name: "foo"
+static_configs:
+- targets: ["foo:9090"]
+- targets: ["bar:9090"]
+`
+	if err := yaml.Unmarshal([]byte(sOne), scrapeConfig); err != nil {
+		t.Fatalf("Unable to load YAML config sOne: %s", err)
+	}
+	called := make(chan struct{})
+
+	ts := NewTargetSet(&mockSyncer{
+		sync: func([]*config.TargetGroup) { called <- struct{}{} },
+	})
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	go ts.Run(ctx)
+
+	ts.UpdateProviders(ProvidersFromConfig(scrapeConfig))
+	<-called
+
+	verifyPresence(ts.tgroups, "static/0/0", true)
+	verifyPresence(ts.tgroups, "static/0/1", true)
+
+	sTwo := `
+job_name: "foo"
+static_configs:
+- targets: ["foo:9090"]
+`
+	if err := yaml.Unmarshal([]byte(sTwo), scrapeConfig); err != nil {
+		t.Fatalf("Unable to load YAML config sTwo: %s", err)
+	}
+
+	ts.UpdateProviders(ProvidersFromConfig(scrapeConfig))
+	<-called
+
+	verifyPresence(ts.tgroups, "static/0/0", true)
+	verifyPresence(ts.tgroups, "static/0/1", false)
+}
+
+type mockSyncer struct {
+	sync func(tgs []*config.TargetGroup)
+}
+
+func (s *mockSyncer) Sync(tgs []*config.TargetGroup) {
+	if s.sync != nil {
+		s.sync(tgs)
+	}
+}
diff --git a/retrieval/discovery/dns/dns.go b/discovery/dns/dns.go
similarity index 100%
rename from retrieval/discovery/dns/dns.go
rename to discovery/dns/dns.go
diff --git a/retrieval/discovery/ec2.go b/discovery/ec2/ec2.go
similarity index 92%
rename from retrieval/discovery/ec2.go
rename to discovery/ec2/ec2.go
index 188909bbc4..2d4138be3d 100644
--- a/retrieval/discovery/ec2.go
+++ b/discovery/ec2/ec2.go
@@ -11,7 +11,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package discovery
+package ec2
 
 import (
 	"fmt"
@@ -50,15 +50,13 @@ const (
 var (
 	ec2SDRefreshFailuresCount = prometheus.NewCounter(
 		prometheus.CounterOpts{
-			Namespace: namespace,
-			Name:      "sd_ec2_refresh_failures_total",
-			Help:      "The number of EC2-SD scrape failures.",
+			Name: "prometheus_sd_ec2_refresh_failures_total",
+			Help: "The number of EC2-SD scrape failures.",
 		})
 	ec2SDRefreshDuration = prometheus.NewSummary(
 		prometheus.SummaryOpts{
-			Namespace: namespace,
-			Name:      "sd_ec2_refresh_duration_seconds",
-			Help:      "The duration of a EC2-SD refresh in seconds.",
+			Name: "prometheus_sd_ec2_refresh_duration_seconds",
+			Help: "The duration of a EC2-SD refresh in seconds.",
 		})
 )
 
@@ -76,8 +74,8 @@ type EC2Discovery struct {
 	port     int
 }
 
-// NewEC2Discovery returns a new EC2Discovery which periodically refreshes its targets.
-func NewEC2Discovery(conf *config.EC2SDConfig) *EC2Discovery {
+// NewDiscovery returns a new EC2Discovery which periodically refreshes its targets.
+func NewDiscovery(conf *config.EC2SDConfig) *EC2Discovery {
 	creds := credentials.NewStaticCredentials(conf.AccessKey, conf.SecretKey, "")
 	if conf.AccessKey == "" && conf.SecretKey == "" {
 		creds = nil
diff --git a/retrieval/discovery/file.go b/discovery/file/file.go
similarity index 94%
rename from retrieval/discovery/file.go
rename to discovery/file/file.go
index ba1ae5b0cf..bcfa4db871 100644
--- a/retrieval/discovery/file.go
+++ b/discovery/file/file.go
@@ -11,7 +11,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package discovery
+package file
 
 import (
 	"encoding/json"
@@ -36,15 +36,13 @@ const fileSDFilepathLabel = model.MetaLabelPrefix + "filepath"
 var (
 	fileSDScanDuration = prometheus.NewSummary(
 		prometheus.SummaryOpts{
-			Namespace: namespace,
-			Name:      "sd_file_scan_duration_seconds",
-			Help:      "The duration of the File-SD scan in seconds.",
+			Name: "prometheus_sd_file_scan_duration_seconds",
+			Help: "The duration of the File-SD scan in seconds.",
 		})
 	fileSDReadErrorsCount = prometheus.NewCounter(
 		prometheus.CounterOpts{
-			Namespace: namespace,
-			Name:      "sd_file_read_errors_total",
-			Help:      "The number of File-SD read errors.",
+			Name: "prometheus_sd_file_read_errors_total",
+			Help: "The number of File-SD read errors.",
 		})
 )
 
@@ -67,8 +65,8 @@ type FileDiscovery struct {
 	lastRefresh map[string]int
 }
 
-// NewFileDiscovery returns a new file discovery for the given paths.
-func NewFileDiscovery(conf *config.FileSDConfig) *FileDiscovery {
+// NewDiscovery returns a new file discovery for the given paths.
+func NewDiscovery(conf *config.FileSDConfig) *FileDiscovery {
 	return &FileDiscovery{
 		paths:    conf.Files,
 		interval: time.Duration(conf.RefreshInterval),
diff --git a/retrieval/discovery/file_test.go b/discovery/file/file_test.go
similarity index 98%
rename from retrieval/discovery/file_test.go
rename to discovery/file/file_test.go
index 9751890679..39ce91f476 100644
--- a/retrieval/discovery/file_test.go
+++ b/discovery/file/file_test.go
@@ -11,7 +11,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package discovery
+package file
 
 import (
 	"fmt"
@@ -41,7 +41,7 @@ func testFileSD(t *testing.T, ext string) {
 	conf.RefreshInterval = model.Duration(1 * time.Hour)
 
 	var (
-		fsd         = NewFileDiscovery(&conf)
+		fsd         = NewDiscovery(&conf)
 		ch          = make(chan []*config.TargetGroup)
 		ctx, cancel = context.WithCancel(context.Background())
 	)
diff --git a/retrieval/discovery/fixtures/target_groups.json b/discovery/file/fixtures/target_groups.json
similarity index 100%
rename from retrieval/discovery/fixtures/target_groups.json
rename to discovery/file/fixtures/target_groups.json
diff --git a/retrieval/discovery/fixtures/target_groups.yml b/discovery/file/fixtures/target_groups.yml
similarity index 100%
rename from retrieval/discovery/fixtures/target_groups.yml
rename to discovery/file/fixtures/target_groups.yml
diff --git a/retrieval/discovery/gce.go b/discovery/gce/gce.go
similarity index 94%
rename from retrieval/discovery/gce.go
rename to discovery/gce/gce.go
index c0f8e311df..1161e4e4b0 100644
--- a/retrieval/discovery/gce.go
+++ b/discovery/gce/gce.go
@@ -11,7 +11,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package discovery
+package gce
 
 import (
 	"fmt"
@@ -52,15 +52,13 @@ const (
 var (
 	gceSDRefreshFailuresCount = prometheus.NewCounter(
 		prometheus.CounterOpts{
-			Namespace: namespace,
-			Name:      "sd_gce_refresh_failures_total",
-			Help:      "The number of GCE-SD refresh failures.",
+			Name: "prometheus_sd_gce_refresh_failures_total",
+			Help: "The number of GCE-SD refresh failures.",
 		})
 	gceSDRefreshDuration = prometheus.NewSummary(
 		prometheus.SummaryOpts{
-			Namespace: namespace,
-			Name:      "sd_gce_refresh_duration",
-			Help:      "The duration of a GCE-SD refresh in seconds.",
+			Name: "prometheus_sd_gce_refresh_duration",
+			Help: "The duration of a GCE-SD refresh in seconds.",
 		})
 )
 
@@ -84,7 +82,7 @@ type GCEDiscovery struct {
 }
 
 // NewGCEDiscovery returns a new GCEDiscovery which periodically refreshes its targets.
-func NewGCEDiscovery(conf *config.GCESDConfig) (*GCEDiscovery, error) {
+func NewDiscovery(conf *config.GCESDConfig) (*GCEDiscovery, error) {
 	gd := &GCEDiscovery{
 		project:      conf.Project,
 		zone:         conf.Zone,
diff --git a/retrieval/discovery/kubernetes/endpoints.go b/discovery/kubernetes/endpoints.go
similarity index 100%
rename from retrieval/discovery/kubernetes/endpoints.go
rename to discovery/kubernetes/endpoints.go
diff --git a/retrieval/discovery/kubernetes/endpoints_test.go b/discovery/kubernetes/endpoints_test.go
similarity index 100%
rename from retrieval/discovery/kubernetes/endpoints_test.go
rename to discovery/kubernetes/endpoints_test.go
diff --git a/retrieval/discovery/kubernetes/kubernetes.go b/discovery/kubernetes/kubernetes.go
similarity index 100%
rename from retrieval/discovery/kubernetes/kubernetes.go
rename to discovery/kubernetes/kubernetes.go
diff --git a/retrieval/discovery/kubernetes/node.go b/discovery/kubernetes/node.go
similarity index 100%
rename from retrieval/discovery/kubernetes/node.go
rename to discovery/kubernetes/node.go
diff --git a/retrieval/discovery/kubernetes/node_test.go b/discovery/kubernetes/node_test.go
similarity index 100%
rename from retrieval/discovery/kubernetes/node_test.go
rename to discovery/kubernetes/node_test.go
diff --git a/retrieval/discovery/kubernetes/pod.go b/discovery/kubernetes/pod.go
similarity index 100%
rename from retrieval/discovery/kubernetes/pod.go
rename to discovery/kubernetes/pod.go
diff --git a/retrieval/discovery/kubernetes/pod_test.go b/discovery/kubernetes/pod_test.go
similarity index 100%
rename from retrieval/discovery/kubernetes/pod_test.go
rename to discovery/kubernetes/pod_test.go
diff --git a/retrieval/discovery/kubernetes/service.go b/discovery/kubernetes/service.go
similarity index 100%
rename from retrieval/discovery/kubernetes/service.go
rename to discovery/kubernetes/service.go
diff --git a/retrieval/discovery/kubernetes/service_test.go b/discovery/kubernetes/service_test.go
similarity index 100%
rename from retrieval/discovery/kubernetes/service_test.go
rename to discovery/kubernetes/service_test.go
diff --git a/retrieval/discovery/marathon/marathon.go b/discovery/marathon/marathon.go
similarity index 100%
rename from retrieval/discovery/marathon/marathon.go
rename to discovery/marathon/marathon.go
diff --git a/retrieval/discovery/marathon/marathon_test.go b/discovery/marathon/marathon_test.go
similarity index 100%
rename from retrieval/discovery/marathon/marathon_test.go
rename to discovery/marathon/marathon_test.go
diff --git a/retrieval/discovery/zookeeper.go b/discovery/zookeeper/zookeeper.go
similarity index 94%
rename from retrieval/discovery/zookeeper.go
rename to discovery/zookeeper/zookeeper.go
index 31f78845f6..eb11f0b98f 100644
--- a/retrieval/discovery/zookeeper.go
+++ b/discovery/zookeeper/zookeeper.go
@@ -11,7 +11,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package discovery
+package zookeeper
 
 import (
 	"encoding/json"
@@ -42,17 +42,17 @@ type ZookeeperDiscovery struct {
 
 // NewNerveDiscovery returns a new NerveDiscovery for the given config.
 func NewNerveDiscovery(conf *config.NerveSDConfig) *ZookeeperDiscovery {
-	return NewZookeeperDiscovery(conf.Servers, time.Duration(conf.Timeout), conf.Paths, parseNerveMember)
+	return NewDiscovery(conf.Servers, time.Duration(conf.Timeout), conf.Paths, parseNerveMember)
 }
 
 // NewServersetDiscovery returns a new ServersetDiscovery for the given config.
 func NewServersetDiscovery(conf *config.ServersetSDConfig) *ZookeeperDiscovery {
-	return NewZookeeperDiscovery(conf.Servers, time.Duration(conf.Timeout), conf.Paths, parseServersetMember)
+	return NewDiscovery(conf.Servers, time.Duration(conf.Timeout), conf.Paths, parseServersetMember)
 }
 
-// NewZookeeperDiscovery returns a new discovery along Zookeeper parses with
+// NewDiscovery returns a new discovery along Zookeeper parses with
 // the given parse function.
-func NewZookeeperDiscovery(
+func NewDiscovery(
 	srvs []string,
 	timeout time.Duration,
 	paths []string,
diff --git a/retrieval/discovery/discovery.go b/retrieval/discovery/discovery.go
deleted file mode 100644
index aebe1e816b..0000000000
--- a/retrieval/discovery/discovery.go
+++ /dev/null
@@ -1,43 +0,0 @@
-// Copyright 2016 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 discovery
-
-import (
-	"github.com/prometheus/common/log"
-	"github.com/prometheus/prometheus/config"
-	"github.com/prometheus/prometheus/retrieval/discovery/consul"
-	"github.com/prometheus/prometheus/retrieval/discovery/dns"
-	"github.com/prometheus/prometheus/retrieval/discovery/kubernetes"
-	"github.com/prometheus/prometheus/retrieval/discovery/marathon"
-)
-
-// NewConsul creates a new Consul based Discovery.
-func NewConsul(cfg *config.ConsulSDConfig) (*consul.Discovery, error) {
-	return consul.NewDiscovery(cfg)
-}
-
-// NewKubernetesDiscovery creates a Kubernetes service discovery based on the passed-in configuration.
-func NewKubernetesDiscovery(conf *config.KubernetesSDConfig) (*kubernetes.Kubernetes, error) {
-	return kubernetes.New(log.Base(), conf)
-}
-
-// NewMarathon creates a new Marathon based discovery.
-func NewMarathon(conf *config.MarathonSDConfig) (*marathon.Discovery, error) {
-	return marathon.NewDiscovery(conf)
-}
-
-// NewDNS creates a new DNS based discovery.
-func NewDNS(conf *config.DNSSDConfig) *dns.Discovery {
-	return dns.NewDiscovery(conf)
-}
diff --git a/retrieval/scrape.go b/retrieval/scrape.go
index 8a9d8899be..24e7fd99c6 100644
--- a/retrieval/scrape.go
+++ b/retrieval/scrape.go
@@ -36,56 +36,46 @@ const (
 	scrapeHealthMetricName   = "up"
 	scrapeDurationMetricName = "scrape_duration_seconds"
 	scrapeSamplesMetricName  = "scrape_samples_scraped"
-
-	// Constants for instrumentation.
-	namespace = "prometheus"
-	interval  = "interval"
-	scrapeJob = "scrape_job"
 )
 
 var (
 	targetIntervalLength = prometheus.NewSummaryVec(
 		prometheus.SummaryOpts{
-			Namespace:  namespace,
-			Name:       "target_interval_length_seconds",
+			Name:       "prometheus_target_interval_length_seconds",
 			Help:       "Actual intervals between scrapes.",
 			Objectives: map[float64]float64{0.01: 0.001, 0.05: 0.005, 0.5: 0.05, 0.90: 0.01, 0.99: 0.001},
 		},
-		[]string{interval},
+		[]string{"interval"},
 	)
 	targetSkippedScrapes = prometheus.NewCounterVec(
 		prometheus.CounterOpts{
-			Namespace: namespace,
-			Name:      "target_skipped_scrapes_total",
-			Help:      "Total number of scrapes that were skipped because the metric storage was throttled.",
+			Name: "prometheus_target_skipped_scrapes_total",
+			Help: "Total number of scrapes that were skipped because the metric storage was throttled.",
 		},
-		[]string{interval},
+		[]string{"interval"},
 	)
 	targetReloadIntervalLength = prometheus.NewSummaryVec(
 		prometheus.SummaryOpts{
-			Namespace:  namespace,
-			Name:       "target_reload_length_seconds",
+			Name:       "prometheus_target_reload_length_seconds",
 			Help:       "Actual interval to reload the scrape pool with a given configuration.",
 			Objectives: map[float64]float64{0.01: 0.001, 0.05: 0.005, 0.5: 0.05, 0.90: 0.01, 0.99: 0.001},
 		},
-		[]string{interval},
+		[]string{"interval"},
 	)
 	targetSyncIntervalLength = prometheus.NewSummaryVec(
 		prometheus.SummaryOpts{
-			Namespace:  namespace,
-			Name:       "target_sync_length_seconds",
+			Name:       "prometheus_target_sync_length_seconds",
 			Help:       "Actual interval to sync the scrape pool.",
 			Objectives: map[float64]float64{0.01: 0.001, 0.05: 0.005, 0.5: 0.05, 0.90: 0.01, 0.99: 0.001},
 		},
-		[]string{scrapeJob},
+		[]string{"scrape_job"},
 	)
 	targetScrapePoolSyncsCounter = prometheus.NewCounterVec(
 		prometheus.CounterOpts{
-			Namespace: namespace,
-			Name:      "target_scrape_pool_sync_total",
-			Help:      "Total number of syncs that were executed on a scrape pool.",
+			Name: "prometheus_target_scrape_pool_sync_total",
+			Help: "Total number of syncs that were executed on a scrape pool.",
 		},
-		[]string{scrapeJob},
+		[]string{"scrape_job"},
 	)
 )
 
@@ -115,7 +105,7 @@ type scrapePool struct {
 	newLoop func(context.Context, scraper, storage.SampleAppender, storage.SampleAppender) loop
 }
 
-func newScrapePool(cfg *config.ScrapeConfig, app storage.SampleAppender) *scrapePool {
+func newScrapePool(ctx context.Context, cfg *config.ScrapeConfig, app storage.SampleAppender) *scrapePool {
 	client, err := NewHTTPClient(cfg)
 	if err != nil {
 		// Any errors that could occur here should be caught during config validation.
@@ -124,6 +114,7 @@ func newScrapePool(cfg *config.ScrapeConfig, app storage.SampleAppender) *scrape
 	return &scrapePool{
 		appender: app,
 		config:   cfg,
+		ctx:      ctx,
 		client:   client,
 		targets:  map[uint64]*Target{},
 		loops:    map[uint64]loop{},
@@ -131,13 +122,6 @@ func newScrapePool(cfg *config.ScrapeConfig, app storage.SampleAppender) *scrape
 	}
 }
 
-func (sp *scrapePool) init(ctx context.Context) {
-	sp.mtx.Lock()
-	defer sp.mtx.Unlock()
-
-	sp.ctx = ctx
-}
-
 // stop terminates all scrape loops and returns after they all terminated.
 func (sp *scrapePool) stop() {
 	var wg sync.WaitGroup
@@ -165,6 +149,7 @@ func (sp *scrapePool) stop() {
 // This method returns after all scrape loops that were stopped have fully terminated.
 func (sp *scrapePool) reload(cfg *config.ScrapeConfig) {
 	start := time.Now()
+
 	sp.mtx.Lock()
 	defer sp.mtx.Unlock()
 
@@ -206,11 +191,32 @@ func (sp *scrapePool) reload(cfg *config.ScrapeConfig) {
 	)
 }
 
+// Sync converts target groups into actual scrape targets and synchronizes
+// the currently running scraper with the resulting set.
+func (sp *scrapePool) Sync(tgs []*config.TargetGroup) {
+	start := time.Now()
+
+	var all []*Target
+	for _, tg := range tgs {
+		targets, err := targetsFromGroup(tg, sp.config)
+		if err != nil {
+			log.With("err", err).Error("creating targets failed")
+			continue
+		}
+		all = append(all, targets...)
+	}
+	sp.sync(all)
+
+	targetSyncIntervalLength.WithLabelValues(sp.config.JobName).Observe(
+		time.Since(start).Seconds(),
+	)
+	targetScrapePoolSyncsCounter.WithLabelValues(sp.config.JobName).Inc()
+}
+
 // sync takes a list of potentially duplicated targets, deduplicates them, starts
 // scrape loops for new targets, and stops scrape loops for disappeared targets.
 // It returns after all stopped scrape loops terminated.
 func (sp *scrapePool) sync(targets []*Target) {
-	start := time.Now()
 	sp.mtx.Lock()
 	defer sp.mtx.Unlock()
 
@@ -256,10 +262,6 @@ func (sp *scrapePool) sync(targets []*Target) {
 	// may be active and tries to insert. The old scraper that didn't terminate yet could still
 	// be inserting a previous sample set.
 	wg.Wait()
-	targetSyncIntervalLength.WithLabelValues(sp.config.JobName).Observe(
-		time.Since(start).Seconds(),
-	)
-	targetScrapePoolSyncsCounter.WithLabelValues(sp.config.JobName).Inc()
 }
 
 // sampleAppender returns an appender for ingested samples from the target.
diff --git a/retrieval/scrape_test.go b/retrieval/scrape_test.go
index 489d73c365..aaa19132f0 100644
--- a/retrieval/scrape_test.go
+++ b/retrieval/scrape_test.go
@@ -36,7 +36,7 @@ func TestNewScrapePool(t *testing.T) {
 	var (
 		app = &nopAppender{}
 		cfg = &config.ScrapeConfig{}
-		sp  = newScrapePool(cfg, app)
+		sp  = newScrapePool(context.Background(), cfg, app)
 	)
 
 	if a, ok := sp.appender.(*nopAppender); !ok || a != app {
@@ -231,7 +231,7 @@ func TestScrapePoolReportAppender(t *testing.T) {
 	target := newTestTarget("example.com:80", 10*time.Millisecond, nil)
 	app := &nopAppender{}
 
-	sp := newScrapePool(cfg, app)
+	sp := newScrapePool(context.Background(), cfg, app)
 
 	cfg.HonorLabels = false
 	wrapped := sp.reportAppender(target)
@@ -266,7 +266,7 @@ func TestScrapePoolSampleAppender(t *testing.T) {
 	target := newTestTarget("example.com:80", 10*time.Millisecond, nil)
 	app := &nopAppender{}
 
-	sp := newScrapePool(cfg, app)
+	sp := newScrapePool(context.Background(), cfg, app)
 
 	cfg.HonorLabels = false
 	wrapped := sp.sampleAppender(target)
diff --git a/retrieval/target.go b/retrieval/target.go
index af66b094ce..01a2bd2626 100644
--- a/retrieval/target.go
+++ b/retrieval/target.go
@@ -17,6 +17,7 @@ import (
 	"fmt"
 	"hash/fnv"
 	"io/ioutil"
+	"net"
 	"net/http"
 	"net/url"
 	"strings"
@@ -276,3 +277,103 @@ func (app relabelAppender) Append(s *model.Sample) error {
 
 	return app.SampleAppender.Append(s)
 }
+
+// populateLabels builds a label set from the given label set and scrape configuration.
+// It returns a label set before relabeling was applied as the second return value.
+// Returns a nil label set if the target is dropped during relabeling.
+func populateLabels(lset model.LabelSet, cfg *config.ScrapeConfig) (res, orig model.LabelSet, err error) {
+	if _, ok := lset[model.AddressLabel]; !ok {
+		return nil, nil, fmt.Errorf("no address")
+	}
+	// Copy labels into the labelset for the target if they are not
+	// set already. Apply the labelsets in order of decreasing precedence.
+	scrapeLabels := model.LabelSet{
+		model.SchemeLabel:      model.LabelValue(cfg.Scheme),
+		model.MetricsPathLabel: model.LabelValue(cfg.MetricsPath),
+		model.JobLabel:         model.LabelValue(cfg.JobName),
+	}
+	for ln, lv := range scrapeLabels {
+		if _, ok := lset[ln]; !ok {
+			lset[ln] = lv
+		}
+	}
+	// Encode scrape query parameters as labels.
+	for k, v := range cfg.Params {
+		if len(v) > 0 {
+			lset[model.LabelName(model.ParamLabelPrefix+k)] = model.LabelValue(v[0])
+		}
+	}
+
+	preRelabelLabels := lset
+	lset = relabel.Process(lset, cfg.RelabelConfigs...)
+
+	// Check if the target was dropped.
+	if lset == nil {
+		return nil, nil, nil
+	}
+
+	// addPort checks whether we should add a default port to the address.
+	// If the address is not valid, we don't append a port either.
+	addPort := func(s string) bool {
+		// If we can split, a port exists and we don't have to add one.
+		if _, _, err := net.SplitHostPort(s); err == nil {
+			return false
+		}
+		// If adding a port makes it valid, the previous error
+		// was not due to an invalid address and we can append a port.
+		_, _, err := net.SplitHostPort(s + ":1234")
+		return err == nil
+	}
+	// If it's an address with no trailing port, infer it based on the used scheme.
+	if addr := string(lset[model.AddressLabel]); addPort(addr) {
+		// Addresses reaching this point are already wrapped in [] if necessary.
+		switch lset[model.SchemeLabel] {
+		case "http", "":
+			addr = addr + ":80"
+		case "https":
+			addr = addr + ":443"
+		default:
+			return nil, nil, fmt.Errorf("invalid scheme: %q", cfg.Scheme)
+		}
+		lset[model.AddressLabel] = model.LabelValue(addr)
+	}
+	if err := config.CheckTargetAddress(lset[model.AddressLabel]); err != nil {
+		return nil, nil, err
+	}
+
+	// Meta labels are deleted after relabelling. Other internal labels propagate to
+	// the target which decides whether they will be part of their label set.
+	for ln := range lset {
+		if strings.HasPrefix(string(ln), model.MetaLabelPrefix) {
+			delete(lset, ln)
+		}
+	}
+
+	// Default the instance label to the target address.
+	if _, ok := lset[model.InstanceLabel]; !ok {
+		lset[model.InstanceLabel] = lset[model.AddressLabel]
+	}
+	return lset, preRelabelLabels, nil
+}
+
+// targetsFromGroup builds targets based on the given TargetGroup and config.
+func targetsFromGroup(tg *config.TargetGroup, cfg *config.ScrapeConfig) ([]*Target, error) {
+	targets := make([]*Target, 0, len(tg.Targets))
+
+	for i, lset := range tg.Targets {
+		// Combine target labels with target group labels.
+		for ln, lv := range tg.Labels {
+			if _, ok := lset[ln]; !ok {
+				lset[ln] = lv
+			}
+		}
+		labels, origLabels, err := populateLabels(lset, cfg)
+		if err != nil {
+			return nil, fmt.Errorf("instance %d in group %s: %s", i, tg, err)
+		}
+		if labels != nil {
+			targets = append(targets, NewTarget(labels, origLabels, cfg.Params))
+		}
+	}
+	return targets, nil
+}
diff --git a/retrieval/targetmanager.go b/retrieval/targetmanager.go
index 4a73ba823f..7d96da02dd 100644
--- a/retrieval/targetmanager.go
+++ b/retrieval/targetmanager.go
@@ -14,39 +14,18 @@
 package retrieval
 
 import (
-	"fmt"
-	"net"
 	"sort"
-	"strings"
 	"sync"
-	"time"
 
 	"github.com/prometheus/common/log"
 	"github.com/prometheus/common/model"
 	"golang.org/x/net/context"
 
 	"github.com/prometheus/prometheus/config"
-	"github.com/prometheus/prometheus/relabel"
-	"github.com/prometheus/prometheus/retrieval/discovery"
+	"github.com/prometheus/prometheus/discovery"
 	"github.com/prometheus/prometheus/storage"
 )
 
-// A TargetProvider provides information about target groups. It maintains a set
-// of sources from which TargetGroups can originate. Whenever a target provider
-// detects a potential change, it sends the TargetGroup through its provided channel.
-//
-// The TargetProvider does not have to guarantee that an actual change happened.
-// It does guarantee that it sends the new TargetGroup whenever a change happens.
-//
-// Providers must initially send all known target groups as soon as it can.
-type TargetProvider interface {
-	// Run hands a channel to the target provider through which it can send
-	// updated target groups. The channel must be closed by the target provider
-	// if no more updates will be sent.
-	// On receiving from done Run must return.
-	Run(ctx context.Context, up chan<- []*config.TargetGroup)
-}
-
 // TargetManager maintains a set of targets, starts and stops their scraping and
 // creates the new targets based on the target groups it receives from various
 // target providers.
@@ -63,6 +42,14 @@ type TargetManager struct {
 	targetSets map[string]*targetSet
 }
 
+type targetSet struct {
+	ctx    context.Context
+	cancel func()
+
+	ts *discovery.TargetSet
+	sp *scrapePool
+}
+
 // NewTargetManager creates a new TargetManager.
 func NewTargetManager(app storage.SampleAppender) *TargetManager {
 	return &TargetManager{
@@ -111,23 +98,33 @@ func (tm *TargetManager) reload() {
 
 		ts, ok := tm.targetSets[scfg.JobName]
 		if !ok {
-			ts = newTargetSet(scfg, tm.appender)
+			ctx, cancel := context.WithCancel(tm.ctx)
+			ts = &targetSet{
+				ctx:    ctx,
+				cancel: cancel,
+				sp:     newScrapePool(ctx, scfg, tm.appender),
+			}
+			ts.ts = discovery.NewTargetSet(ts.sp)
+
 			tm.targetSets[scfg.JobName] = ts
 
 			tm.wg.Add(1)
 
 			go func(ts *targetSet) {
-				ts.runScraping(tm.ctx)
+				// Run target set, which blocks until its context is canceled.
+				// Gracefully shut down pending scrapes in the scrape pool afterwards.
+				ts.ts.Run(ctx)
+				ts.sp.stop()
 				tm.wg.Done()
 			}(ts)
 		} else {
-			ts.reload(scfg)
+			ts.sp.reload(scfg)
 		}
-		ts.runProviders(tm.ctx, providersFromConfig(scfg))
+		ts.ts.UpdateProviders(discovery.ProvidersFromConfig(scfg))
 	}
 
-	// Remove old target sets. Waiting for stopping is already guaranteed
-	// by the goroutine that started the target set.
+	// Remove old target sets. Waiting for scrape pools to complete pending
+	// scrape inserts is already guaranteed by the goroutine that started the target set.
 	for name, ts := range tm.targetSets {
 		if _, ok := jobs[name]; !ok {
 			ts.cancel()
@@ -145,14 +142,14 @@ func (tm *TargetManager) Pools() map[string]Targets {
 
 	// TODO(fabxc): this is just a hack to maintain compatibility for now.
 	for _, ps := range tm.targetSets {
-		ps.scrapePool.mtx.RLock()
+		ps.sp.mtx.RLock()
 
-		for _, t := range ps.scrapePool.targets {
+		for _, t := range ps.sp.targets {
 			job := string(t.Labels()[model.JobLabel])
 			pools[job] = append(pools[job], t)
 		}
 
-		ps.scrapePool.mtx.RUnlock()
+		ps.sp.mtx.RUnlock()
 	}
 	for _, targets := range pools {
 		sort.Sort(targets)
@@ -173,385 +170,3 @@ func (tm *TargetManager) ApplyConfig(cfg *config.Config) error {
 	}
 	return nil
 }
-
-// targetSet holds several TargetProviders for which the same scrape configuration
-// is used. It maintains target groups from all given providers and sync them
-// to a scrape pool.
-type targetSet struct {
-	mtx sync.RWMutex
-
-	// Sets of targets by a source string that is unique across target providers.
-	tgroups map[string][]*Target
-
-	scrapePool *scrapePool
-	config     *config.ScrapeConfig
-
-	syncCh          chan struct{}
-	cancelScraping  func()
-	cancelProviders func()
-}
-
-func newTargetSet(cfg *config.ScrapeConfig, app storage.SampleAppender) *targetSet {
-	ts := &targetSet{
-		scrapePool: newScrapePool(cfg, app),
-		syncCh:     make(chan struct{}, 1),
-		config:     cfg,
-	}
-	return ts
-}
-
-func (ts *targetSet) cancel() {
-	ts.mtx.RLock()
-	defer ts.mtx.RUnlock()
-
-	if ts.cancelScraping != nil {
-		ts.cancelScraping()
-	}
-	if ts.cancelProviders != nil {
-		ts.cancelProviders()
-	}
-}
-
-func (ts *targetSet) reload(cfg *config.ScrapeConfig) {
-	ts.mtx.Lock()
-	ts.config = cfg
-	ts.mtx.Unlock()
-
-	ts.scrapePool.reload(cfg)
-}
-
-func (ts *targetSet) runScraping(ctx context.Context) {
-	ctx, ts.cancelScraping = context.WithCancel(ctx)
-
-	ts.scrapePool.init(ctx)
-
-Loop:
-	for {
-		// Throttle syncing to once per five seconds.
-		select {
-		case <-ctx.Done():
-			break Loop
-		case <-time.After(5 * time.Second):
-		}
-
-		select {
-		case <-ctx.Done():
-			break Loop
-		case <-ts.syncCh:
-			ts.mtx.RLock()
-			ts.sync()
-			ts.mtx.RUnlock()
-		}
-	}
-
-	// We want to wait for all pending target scrapes to complete though to ensure there'll
-	// be no more storage writes after this point.
-	ts.scrapePool.stop()
-}
-
-func (ts *targetSet) sync() {
-	var all []*Target
-	for _, targets := range ts.tgroups {
-		all = append(all, targets...)
-	}
-	ts.scrapePool.sync(all)
-}
-
-func (ts *targetSet) runProviders(ctx context.Context, providers map[string]TargetProvider) {
-	// Lock for the entire time. This may mean up to 5 seconds until the full initial set
-	// is retrieved and applied.
-	// We could release earlier with some tweaks, but this is easier to reason about.
-	ts.mtx.Lock()
-	defer ts.mtx.Unlock()
-
-	var wg sync.WaitGroup
-
-	if ts.cancelProviders != nil {
-		ts.cancelProviders()
-	}
-	ctx, ts.cancelProviders = context.WithCancel(ctx)
-
-	// (Re-)create a fresh tgroups map to not keep stale targets around. We
-	// will retrieve all targets below anyway, so cleaning up everything is
-	// safe and doesn't inflict any additional cost.
-	ts.tgroups = map[string][]*Target{}
-
-	for name, prov := range providers {
-		wg.Add(1)
-
-		updates := make(chan []*config.TargetGroup)
-
-		go func(name string, prov TargetProvider) {
-			select {
-			case <-ctx.Done():
-			case initial, ok := <-updates:
-				// Handle the case that a target provider exits and closes the channel
-				// before the context is done.
-				if !ok {
-					break
-				}
-				// First set of all targets the provider knows.
-				for _, tgroup := range initial {
-					if tgroup == nil {
-						continue
-					}
-					targets, err := targetsFromGroup(tgroup, ts.config)
-					if err != nil {
-						log.With("target_group", tgroup).Errorf("Target update failed: %s", err)
-						continue
-					}
-					ts.tgroups[name+"/"+tgroup.Source] = targets
-				}
-			case <-time.After(5 * time.Second):
-				// Initial set didn't arrive. Act as if it was empty
-				// and wait for updates later on.
-			}
-
-			wg.Done()
-
-			// Start listening for further updates.
-			for {
-				select {
-				case <-ctx.Done():
-					return
-				case tgs, ok := <-updates:
-					// Handle the case that a target provider exits and closes the channel
-					// before the context is done.
-					if !ok {
-						return
-					}
-					for _, tg := range tgs {
-						if err := ts.update(name, tg); err != nil {
-							log.With("target_group", tg).Errorf("Target update failed: %s", err)
-						}
-					}
-				}
-			}
-		}(name, prov)
-
-		go prov.Run(ctx, updates)
-	}
-
-	// We wait for a full initial set of target groups before releasing the mutex
-	// to ensure the initial sync is complete and there are no races with subsequent updates.
-	wg.Wait()
-	// Just signal that there are initial sets to sync now. Actual syncing must only
-	// happen in the runScraping loop.
-	select {
-	case ts.syncCh <- struct{}{}:
-	default:
-	}
-}
-
-// update handles a target group update from a target provider identified by the name.
-func (ts *targetSet) update(name string, tgroup *config.TargetGroup) error {
-	if tgroup == nil {
-		return nil
-	}
-	targets, err := targetsFromGroup(tgroup, ts.config)
-	if err != nil {
-		return err
-	}
-
-	ts.mtx.Lock()
-	defer ts.mtx.Unlock()
-
-	ts.tgroups[name+"/"+tgroup.Source] = targets
-
-	select {
-	case ts.syncCh <- struct{}{}:
-	default:
-	}
-
-	return nil
-}
-
-// providersFromConfig returns all TargetProviders configured in cfg.
-func providersFromConfig(cfg *config.ScrapeConfig) map[string]TargetProvider {
-	providers := map[string]TargetProvider{}
-
-	app := func(mech string, i int, tp TargetProvider) {
-		providers[fmt.Sprintf("%s/%d", mech, i)] = tp
-	}
-
-	for i, c := range cfg.DNSSDConfigs {
-		app("dns", i, discovery.NewDNS(c))
-	}
-	for i, c := range cfg.FileSDConfigs {
-		app("file", i, discovery.NewFileDiscovery(c))
-	}
-	for i, c := range cfg.ConsulSDConfigs {
-		k, err := discovery.NewConsul(c)
-		if err != nil {
-			log.Errorf("Cannot create Consul discovery: %s", err)
-			continue
-		}
-		app("consul", i, k)
-	}
-	for i, c := range cfg.MarathonSDConfigs {
-		m, err := discovery.NewMarathon(c)
-		if err != nil {
-			log.Errorf("Cannot create Marathon discovery: %s", err)
-			continue
-		}
-		app("marathon", i, m)
-	}
-	for i, c := range cfg.KubernetesSDConfigs {
-		k, err := discovery.NewKubernetesDiscovery(c)
-		if err != nil {
-			log.Errorf("Cannot create Kubernetes discovery: %s", err)
-			continue
-		}
-		app("kubernetes", i, k)
-	}
-	for i, c := range cfg.ServersetSDConfigs {
-		app("serverset", i, discovery.NewServersetDiscovery(c))
-	}
-	for i, c := range cfg.NerveSDConfigs {
-		app("nerve", i, discovery.NewNerveDiscovery(c))
-	}
-	for i, c := range cfg.EC2SDConfigs {
-		app("ec2", i, discovery.NewEC2Discovery(c))
-	}
-	for i, c := range cfg.GCESDConfigs {
-		gced, err := discovery.NewGCEDiscovery(c)
-		if err != nil {
-			log.Errorf("Cannot initialize GCE discovery: %s", err)
-			continue
-		}
-		app("gce", i, gced)
-	}
-	for i, c := range cfg.AzureSDConfigs {
-		app("azure", i, discovery.NewAzureDiscovery(c))
-	}
-	if len(cfg.StaticConfigs) > 0 {
-		app("static", 0, NewStaticProvider(cfg.StaticConfigs))
-	}
-
-	return providers
-}
-
-// populateLabels builds a label set from the given label set and scrape configuration.
-// It returns a label set before relabeling was applied as the second return value.
-// Returns a nil label set if the target is dropped during relabeling.
-func populateLabels(lset model.LabelSet, cfg *config.ScrapeConfig) (res, orig model.LabelSet, err error) {
-	if _, ok := lset[model.AddressLabel]; !ok {
-		return nil, nil, fmt.Errorf("no address")
-	}
-	// Copy labels into the labelset for the target if they are not
-	// set already. Apply the labelsets in order of decreasing precedence.
-	scrapeLabels := model.LabelSet{
-		model.SchemeLabel:      model.LabelValue(cfg.Scheme),
-		model.MetricsPathLabel: model.LabelValue(cfg.MetricsPath),
-		model.JobLabel:         model.LabelValue(cfg.JobName),
-	}
-	for ln, lv := range scrapeLabels {
-		if _, ok := lset[ln]; !ok {
-			lset[ln] = lv
-		}
-	}
-	// Encode scrape query parameters as labels.
-	for k, v := range cfg.Params {
-		if len(v) > 0 {
-			lset[model.LabelName(model.ParamLabelPrefix+k)] = model.LabelValue(v[0])
-		}
-	}
-
-	preRelabelLabels := lset
-	lset = relabel.Process(lset, cfg.RelabelConfigs...)
-
-	// Check if the target was dropped.
-	if lset == nil {
-		return nil, nil, nil
-	}
-
-	// addPort checks whether we should add a default port to the address.
-	// If the address is not valid, we don't append a port either.
-	addPort := func(s string) bool {
-		// If we can split, a port exists and we don't have to add one.
-		if _, _, err := net.SplitHostPort(s); err == nil {
-			return false
-		}
-		// If adding a port makes it valid, the previous error
-		// was not due to an invalid address and we can append a port.
-		_, _, err := net.SplitHostPort(s + ":1234")
-		return err == nil
-	}
-	// If it's an address with no trailing port, infer it based on the used scheme.
-	if addr := string(lset[model.AddressLabel]); addPort(addr) {
-		// Addresses reaching this point are already wrapped in [] if necessary.
-		switch lset[model.SchemeLabel] {
-		case "http", "":
-			addr = addr + ":80"
-		case "https":
-			addr = addr + ":443"
-		default:
-			return nil, nil, fmt.Errorf("invalid scheme: %q", cfg.Scheme)
-		}
-		lset[model.AddressLabel] = model.LabelValue(addr)
-	}
-	if err := config.CheckTargetAddress(lset[model.AddressLabel]); err != nil {
-		return nil, nil, err
-	}
-
-	// Meta labels are deleted after relabelling. Other internal labels propagate to
-	// the target which decides whether they will be part of their label set.
-	for ln := range lset {
-		if strings.HasPrefix(string(ln), model.MetaLabelPrefix) {
-			delete(lset, ln)
-		}
-	}
-
-	// Default the instance label to the target address.
-	if _, ok := lset[model.InstanceLabel]; !ok {
-		lset[model.InstanceLabel] = lset[model.AddressLabel]
-	}
-	return lset, preRelabelLabels, nil
-}
-
-// targetsFromGroup builds targets based on the given TargetGroup and config.
-func targetsFromGroup(tg *config.TargetGroup, cfg *config.ScrapeConfig) ([]*Target, error) {
-	targets := make([]*Target, 0, len(tg.Targets))
-
-	for i, lset := range tg.Targets {
-		// Combine target labels with target group labels.
-		for ln, lv := range tg.Labels {
-			if _, ok := lset[ln]; !ok {
-				lset[ln] = lv
-			}
-		}
-		labels, origLabels, err := populateLabels(lset, cfg)
-		if err != nil {
-			return nil, fmt.Errorf("instance %d in group %s: %s", i, tg, err)
-		}
-		if labels != nil {
-			targets = append(targets, NewTarget(labels, origLabels, cfg.Params))
-		}
-	}
-	return targets, nil
-}
-
-// StaticProvider holds a list of target groups that never change.
-type StaticProvider struct {
-	TargetGroups []*config.TargetGroup
-}
-
-// NewStaticProvider returns a StaticProvider configured with the given
-// target groups.
-func NewStaticProvider(groups []*config.TargetGroup) *StaticProvider {
-	for i, tg := range groups {
-		tg.Source = fmt.Sprintf("%d", i)
-	}
-	return &StaticProvider{groups}
-}
-
-// Run implements the TargetProvider interface.
-func (sd *StaticProvider) Run(ctx context.Context, ch chan<- []*config.TargetGroup) {
-	// We still have to consider that the consumer exits right away in which case
-	// the context will be canceled.
-	select {
-	case ch <- sd.TargetGroups:
-	case <-ctx.Done():
-	}
-	close(ch)
-}
diff --git a/retrieval/targetmanager_test.go b/retrieval/targetmanager_test.go
index 65e5d6f2d1..dc4568a955 100644
--- a/retrieval/targetmanager_test.go
+++ b/retrieval/targetmanager_test.go
@@ -17,64 +17,10 @@ import (
 	"reflect"
 	"testing"
 
-	"golang.org/x/net/context"
-	"gopkg.in/yaml.v2"
-
 	"github.com/prometheus/common/model"
 	"github.com/prometheus/prometheus/config"
-	"github.com/prometheus/prometheus/storage/local"
 )
 
-func TestTargetSetRecreatesTargetGroupsEveryRun(t *testing.T) {
-
-	verifyPresence := func(tgroups map[string][]*Target, name string, present bool) {
-		if _, ok := tgroups[name]; ok != present {
-			msg := ""
-			if !present {
-				msg = "not "
-			}
-			t.Fatalf("'%s' should %sbe present in TargetSet.tgroups: %s", name, msg, tgroups)
-		}
-
-	}
-
-	scrapeConfig := &config.ScrapeConfig{}
-
-	sOne := `
-job_name: "foo"
-static_configs:
-- targets: ["foo:9090"]
-- targets: ["bar:9090"]
-`
-	if err := yaml.Unmarshal([]byte(sOne), scrapeConfig); err != nil {
-		t.Fatalf("Unable to load YAML config sOne: %s", err)
-	}
-
-	// Not properly setting it up, but that seems okay
-	mss := &local.MemorySeriesStorage{}
-
-	ts := newTargetSet(scrapeConfig, mss)
-
-	ts.runProviders(context.Background(), providersFromConfig(scrapeConfig))
-
-	verifyPresence(ts.tgroups, "static/0/0", true)
-	verifyPresence(ts.tgroups, "static/0/1", true)
-
-	sTwo := `
-job_name: "foo"
-static_configs:
-- targets: ["foo:9090"]
-`
-	if err := yaml.Unmarshal([]byte(sTwo), scrapeConfig); err != nil {
-		t.Fatalf("Unable to load YAML config sTwo: %s", err)
-	}
-
-	ts.runProviders(context.Background(), providersFromConfig(scrapeConfig))
-
-	verifyPresence(ts.tgroups, "static/0/0", true)
-	verifyPresence(ts.tgroups, "static/0/1", false)
-}
-
 func mustNewRegexp(s string) config.Regexp {
 	re, err := config.NewRegexp(s)
 	if err != nil {