[receiver/prometheus] Use confighttp for target allocator client (ope…

…n-telemetry#31452)

**Description:** 
Use confighttp for target allocator http client in prometheus receiver.

**Link to tracking Issue:**
open-telemetry#31449

**Testing:**
Added some simple config tests.

**Documentation:**
Added a note to the README.

.chloggen/receiver_prometheus_confighttp-ta.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: prometheusreceiver
+
+# A brief description of the change. Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Use confighttp for target allocator client
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [31449]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

receiver/prometheusreceiver/README.md

@@ -141,6 +141,11 @@ receivers:
  interval: 30s
  collector_id: collector-1
 ```
+
+The `target_allocator` section embeds the full [confighttp client configuration][confighttp].
+
+[confighttp]: https://github.com/open-telemetry/opentelemetry-collector/tree/main/config/confighttp#client-configuration
+
 ## Exemplars
 This receiver accepts exemplars coming in Prometheus format and converts it to OTLP format.
 1. Value is expected to be received in `float64` format

receiver/prometheusreceiver/config.go

@@ -16,6 +16,7 @@ import (
  promconfig "github.com/prometheus/prometheus/config"
  promHTTP "github.com/prometheus/prometheus/discovery/http"
  "github.com/prometheus/prometheus/discovery/kubernetes"
+ "go.opentelemetry.io/collector/config/confighttp"
  "go.opentelemetry.io/collector/confmap"
  "gopkg.in/yaml.v2"
 )
@@ -52,10 +53,10 @@ func (cfg *Config) Validate() error {
 }
 
 type TargetAllocator struct {
- Endpoint string `mapstructure:"endpoint"`
- Interval time.Duration `mapstructure:"interval"`
- CollectorID string `mapstructure:"collector_id"`
- HTTPSDConfig *PromHTTPSDConfig `mapstructure:"http_sd_config"`
+ confighttp.ClientConfig `mapstructure:",squash"`
+ Interval  time.Duration `mapstructure:"interval"`
+ CollectorID  string `mapstructure:"collector_id"`
+ HTTPSDConfig  *PromHTTPSDConfig `mapstructure:"http_sd_config"`
 }
 
 func (cfg *TargetAllocator) Validate() error {

receiver/prometheusreceiver/config_test.go

@@ -71,8 +71,11 @@ func TestLoadTargetAllocatorConfig(t *testing.T) {
  r0 := cfg.(*Config)
  assert.NotNil(t, r0.PrometheusConfig)
  assert.Equal(t, "http:https://localhost:8080", r0.TargetAllocator.Endpoint)
+ assert.Equal(t, 5*time.Second, r0.TargetAllocator.Timeout)
+ assert.Equal(t, "client.crt", r0.TargetAllocator.TLSSetting.CertFile)
  assert.Equal(t, 30*time.Second, r0.TargetAllocator.Interval)
  assert.Equal(t, "collector-1", r0.TargetAllocator.CollectorID)
+ assert.NotNil(t, r0.PrometheusConfig)
 
  sub, err = cm.Sub(component.NewIDWithName(metadata.Type, "withScrape").String())
  require.NoError(t, err)

receiver/prometheusreceiver/go.mod

@@ -14,6 +14,7 @@ require (
  github.com/prometheus/prometheus v0.48.1
  github.com/stretchr/testify v1.9.0
  go.opentelemetry.io/collector/component v0.96.1-0.20240306115632-b2693620eff6
+ go.opentelemetry.io/collector/config/confighttp v0.96.1-0.20240306115632-b2693620eff6
  go.opentelemetry.io/collector/confmap v0.96.1-0.20240306115632-b2693620eff6
  go.opentelemetry.io/collector/confmap/provider/fileprovider v0.96.1-0.20240306115632-b2693620eff6
  go.opentelemetry.io/collector/consumer v0.96.1-0.20240306115632-b2693620eff6
@@ -162,7 +163,6 @@ require (
  go.opentelemetry.io/collector v0.96.1-0.20240306115632-b2693620eff6 // indirect
  go.opentelemetry.io/collector/config/configauth v0.96.1-0.20240306115632-b2693620eff6 // indirect
  go.opentelemetry.io/collector/config/configcompression v0.96.1-0.20240306115632-b2693620eff6 // indirect
- go.opentelemetry.io/collector/config/confighttp v0.96.1-0.20240306115632-b2693620eff6 // indirect
  go.opentelemetry.io/collector/config/configopaque v1.3.1-0.20240306115632-b2693620eff6 // indirect
  go.opentelemetry.io/collector/config/configretry v0.96.1-0.20240306115632-b2693620eff6 // indirect
  go.opentelemetry.io/collector/config/configtelemetry v0.96.1-0.20240306115632-b2693620eff6 // indirect

receiver/prometheusreceiver/metrics_receiver.go

@@ -50,6 +50,7 @@ type pReceiver struct {
  settings receiver.CreateSettings
  scrapeManager *scrape.Manager
  discoveryManager *discovery.Manager
+ httpClient *http.Client
 }
 
 // New creates a new prometheus.Receiver reference.
@@ -66,7 +67,7 @@ func newPrometheusReceiver(set receiver.CreateSettings, cfg *Config, next consum
 
 // Start is the method that starts Prometheus scraping. It
 // is controlled by having previously defined a Configuration using perhaps New.
-func (r *pReceiver) Start(_ context.Context, _ component.Host) error {
+func (r *pReceiver) Start(_ context.Context, host component.Host) error {
  discoveryCtx, cancel := context.WithCancel(context.Background())
  r.cancelFunc = cancel
 
@@ -89,6 +90,11 @@ func (r *pReceiver) Start(_ context.Context, _ component.Host) error {
 
  allocConf := r.cfg.TargetAllocator
  if allocConf != nil {
+ r.httpClient, err = r.cfg.TargetAllocator.ToClient(host, r.settings.TelemetrySettings)
+ if err != nil {
+ r.settings.Logger.Error("Failed to create http client", zap.Error(err))
+ return err
+ }
  err = r.startTargetAllocator(allocConf, baseCfg)
  if err != nil {
  return err
@@ -197,7 +203,7 @@ func (r *pReceiver) getScrapeConfigsResponse(baseURL string) (map[string]*config
  return nil, err
  }
 
- resp, err := http.Get(scrapeConfigsURL) //nolint
+ resp, err := r.httpClient.Get(scrapeConfigsURL)
  if err != nil {
  return nil, err
  }

receiver/prometheusreceiver/testdata/config_target_allocator.yaml

@@ -1,6 +1,9 @@
 prometheus:
  target_allocator:
  endpoint: http:https://localhost:8080
+ timeout: 5s
+ tls:
+ cert_file: "client.crt"
  interval: 30s
  collector_id: collector-1
 prometheus/withScrape: