lib/promscrape: add follow_redirect option to scrape_configs section like Prometheus does

See https://github.com/prometheus/prometheus/pull/8546

docs/CHANGELOG.md

@@ -3,6 +3,8 @@
 # tip
 
 * FEATURE: vminsert and vmagent: add `-sortLabels` command-line flag for sorting metric labels before pushing them to `vmstorage`. This should reduce the size of `MetricName -> internal_series_id` cache (aka `vm_cache_size_bytes{type="storage/tsid"}`) when ingesting samples for the same time series with distinct order of labels. For example, `foo{k1="v1",k2="v2"}` and `foo{k2="v2",k1="v1"}` represent a single time series.
+* FEATURE: update Go builder from `v1.16.2` to `v1.16.3`. This should fix [these issues](https://github.com/golang/go/issues?q=milestone%3AGo1.16.3+label%3ACherryPickApproved).
+* FEATURE: vmagent: add support for `follow_redirects` option to `scrape_configs` section in the same way as [Prometheus does](https://github.com/prometheus/prometheus/pull/8546).
 * FEATURE: vmagent: reduce memory usage when `-remoteWrite.queues` is set to a big value. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/1167).
 * FEATURE: vmagent: add AWS IAM roles for tasks support for EC2 service discovery according to [these docs](https://docs.aws.amazon.com/AmazonECS/latest/developerguide/task-iam-roles.html).
 

lib/promscrape/client.go

@@ -46,6 +46,7 @@ type client struct {
 	host               string
 	requestURI         string
 	authHeader         string
+	denyRedirects      bool
 	disableCompression bool
 	disableKeepAlive   bool
 }
@@ -101,6 +102,11 @@ func newClient(sw *ScrapeWork) *client {
 			},
 			Timeout: sw.ScrapeTimeout,
 		}
+		if sw.DenyRedirects {
+			sc.CheckRedirect = func(req *http.Request, via []*http.Request) error {
+				return http.ErrUseLastResponse
+			}
+		}
 	}
 	return &client{
 		hc:                 hc,
@@ -109,6 +115,7 @@ func newClient(sw *ScrapeWork) *client {
 		host:               host,
 		requestURI:         requestURI,
 		authHeader:         sw.AuthConfig.Authorization,
+		denyRedirects:      sw.DenyRedirects,
 		disableCompression: sw.DisableCompression,
 		disableKeepAlive:   sw.DisableKeepAlive,
 	}
@@ -181,13 +188,17 @@ func (c *client) ReadData(dst []byte) ([]byte, error) {
 	err := doRequestWithPossibleRetry(c.hc, req, resp, deadline)
 	statusCode := resp.StatusCode()
 	if err == nil && (statusCode == fasthttp.StatusMovedPermanently || statusCode == fasthttp.StatusFound) {
-		// Allow a single redirect.
-		// It is expected that the redirect is made on the same host.
-		// Otherwise it won't work.
-		if location := resp.Header.Peek("Location"); len(location) > 0 {
-			req.URI().UpdateBytes(location)
-			err = c.hc.DoDeadline(req, resp, deadline)
-			statusCode = resp.StatusCode()
+		if c.denyRedirects {
+			err = fmt.Errorf("cannot follow redirects if `follow_redirects: false` is set")
+		} else {
+			// Allow a single redirect.
+			// It is expected that the redirect is made on the same host.
+			// Otherwise it won't work.
+			if location := resp.Header.Peek("Location"); len(location) > 0 {
+				req.URI().UpdateBytes(location)
+				err = c.hc.DoDeadline(req, resp, deadline)
+				statusCode = resp.StatusCode()
+			}
 		}
 	}
 	if swapResponseBodies {

lib/promscrape/config.go

@@ -88,6 +88,7 @@ type ScrapeConfig struct {
 	MetricsPath          string                      `yaml:"metrics_path,omitempty"`
 	HonorLabels          bool                        `yaml:"honor_labels,omitempty"`
 	HonorTimestamps      bool                        `yaml:"honor_timestamps,omitempty"`
+	FollowRedirects      *bool                       `yaml:"follow_redirects"` // omitempty isn't set, since the default value for this flag is true.
 	Scheme               string                      `yaml:"scheme,omitempty"`
 	Params               map[string][]string         `yaml:"params,omitempty"`
 	BasicAuth            *promauth.BasicAuthConfig   `yaml:"basic_auth,omitempty"`
@@ -531,6 +532,10 @@ func getScrapeWorkConfig(sc *ScrapeConfig, baseDir string, globalCfg *GlobalConf
 	}
 	honorLabels := sc.HonorLabels
 	honorTimestamps := sc.HonorTimestamps
+	denyRedirects := false
+	if sc.FollowRedirects != nil {
+		denyRedirects = !*sc.FollowRedirects
+	}
 	metricsPath := sc.MetricsPath
 	if metricsPath == "" {
 		metricsPath = "/metrics"
@@ -571,6 +576,7 @@ func getScrapeWorkConfig(sc *ScrapeConfig, baseDir string, globalCfg *GlobalConf
 		authConfig:           ac,
 		honorLabels:          honorLabels,
 		honorTimestamps:      honorTimestamps,
+		denyRedirects:        denyRedirects,
 		externalLabels:       globalCfg.ExternalLabels,
 		relabelConfigs:       relabelConfigs,
 		metricRelabelConfigs: metricRelabelConfigs,
@@ -596,6 +602,7 @@ type scrapeWorkConfig struct {
 	authConfig           *promauth.Config
 	honorLabels          bool
 	honorTimestamps      bool
+	denyRedirects        bool
 	externalLabels       map[string]string
 	relabelConfigs       *promrelabel.ParsedConfigs
 	metricRelabelConfigs *promrelabel.ParsedConfigs
@@ -856,6 +863,7 @@ func (swc *scrapeWorkConfig) getScrapeWork(target string, extraLabels, metaLabel
 		ScrapeTimeout:        swc.scrapeTimeout,
 		HonorLabels:          swc.honorLabels,
 		HonorTimestamps:      swc.honorTimestamps,
+		DenyRedirects:        swc.denyRedirects,
 		OriginalLabels:       originalLabels,
 		Labels:               labels,
 		ProxyURL:             swc.proxyURL,

lib/promscrape/config_test.go

@@ -751,6 +751,7 @@ scrape_configs:
   scheme: https
   honor_labels: true
   honor_timestamps: true
+  follow_redirects: false
   params:
     p: ["x&y", "="]
     xaa:
@@ -779,6 +780,7 @@ scrape_configs:
 			ScrapeTimeout:   12 * time.Second,
 			HonorLabels:     true,
 			HonorTimestamps: true,
+			DenyRedirects:   true,
 			Labels: []prompbmarshal.Label{
 				{
 					Name:  "__address__",
@@ -824,6 +826,7 @@ scrape_configs:
 			ScrapeTimeout:   12 * time.Second,
 			HonorLabels:     true,
 			HonorTimestamps: true,
+			DenyRedirects:   true,
 			Labels: []prompbmarshal.Label{
 				{
 					Name:  "__address__",

lib/promscrape/scrapework.go

@@ -48,6 +48,9 @@ type ScrapeWork struct {
 	// See https://prometheus.io/docs/prometheus/latest/configuration/configuration/#scrape_config
 	HonorTimestamps bool
 
+	// Whether to deny redirects during requests to scrape config.
+	DenyRedirects bool
+
 	// OriginalLabels contains original labels before relabeling.
 	//
 	// These labels are needed for relabeling troubleshooting at /targets page.
@@ -107,10 +110,10 @@ type ScrapeWork struct {
 // it can be used for comparing for equality for two ScrapeWork objects.
 func (sw *ScrapeWork) key() string {
 	// Do not take into account OriginalLabels.
-	key := fmt.Sprintf("ScrapeURL=%s, ScrapeInterval=%s, ScrapeTimeout=%s, HonorLabels=%v, HonorTimestamps=%v, Labels=%s, "+
+	key := fmt.Sprintf("ScrapeURL=%s, ScrapeInterval=%s, ScrapeTimeout=%s, HonorLabels=%v, HonorTimestamps=%v, DenyRedirects=%v, Labels=%s, "+
 		"ProxyURL=%s, ProxyAuthConfig=%s, AuthConfig=%s, MetricRelabelConfigs=%s, SampleLimit=%d, DisableCompression=%v, DisableKeepAlive=%v, StreamParse=%v, "+
 		"ScrapeAlignInterval=%s, ScrapeOffset=%s",
-		sw.ScrapeURL, sw.ScrapeInterval, sw.ScrapeTimeout, sw.HonorLabels, sw.HonorTimestamps, sw.LabelsString(),
+		sw.ScrapeURL, sw.ScrapeInterval, sw.ScrapeTimeout, sw.HonorLabels, sw.HonorTimestamps, sw.DenyRedirects, sw.LabelsString(),
 		sw.ProxyURL.String(), sw.ProxyAuthConfig.String(),
 		sw.AuthConfig.String(), sw.MetricRelabelConfigs.String(), sw.SampleLimit, sw.DisableCompression, sw.DisableKeepAlive, sw.StreamParse,
 		sw.ScrapeAlignInterval, sw.ScrapeOffset)