Add collect[] parameter (#699)

* Add `collect[]` parameter

* Add TODo comment about staticcheck ignored

* Restore promhttp.HandlerOpts

* Log a warning and return HTTP error instead of failing

* Check collector existence and status, cleanups

* Fix warnings and error messages

* Don't panic, return error if collector registration failed

* Update README

Makefile

@@ -27,6 +27,10 @@ DOCKER_IMAGE_TAG        ?= $(subst /,-,$(shell git rev-parse --abbrev-ref HEAD))
 MACH                    ?= $(shell uname -m)
 DOCKERFILE              ?= Dockerfile
 
+# TODO: Remove deprecated and problematic InstrumentHandlerFunc usage.
+STATICCHECK_IGNORE = \
+  github.com/prometheus/node_exporter/node_exporter.go:SA1019
+
 ifeq ($(GOHOSTARCH),amd64)
 	# Only supported on amd64
 	test-flags := -race
@@ -99,7 +103,7 @@ vet:
 
 staticcheck: $(STATICCHECK)
 	@echo ">> running staticcheck"
-	@$(STATICCHECK) $(pkgs)
+	@$(STATICCHECK) -ignore "$(STATICCHECK_IGNORE)" $(pkgs)
 
 build: $(PROMU)
 	@echo ">> building binaries"

README.md

@@ -107,6 +107,39 @@ echo 'role{role="application_server"} 1' > /path/to/directory/role.prom.$$
 mv /path/to/directory/role.prom.$$ /path/to/directory/role.prom
 ```
 
+### Filtering enabled collectors
+
+The node_exporter will expose all metrics from enabled collectors by default, but it can be passed an optional list of collectors to filter metrics. The `collect[]` parameter accepts values matching enabled collector names.
+
+This can be useful for specifying different scrape intervals for different collectors in Prometheus:
+
+```yaml
+scrape_configs:
+  - job_name: 'node resources'
+    scrape_interval: 15s
+    static_configs:
+      - targets:
+        - '192.168.1.2:9100'
+    params:
+      collect[]:
+        - cpu
+        - meminfo
+        - diskstats
+        - netdev
+        - netstat
+
+  - job_name: 'node storage'
+    scrape_interval: 1m
+    static_configs:
+      - targets:
+        - '192.168.1.2:9100'
+    params:
+      collect[]:
+        - filefd
+        - filesystem
+        - xfs
+```
+
 ## Building and running
 
 Prerequisites:

collector/collector.go

@@ -80,15 +80,28 @@ type nodeCollector struct {
 }
 
 // NewNodeCollector creates a new NodeCollector
-func NewNodeCollector() (*nodeCollector, error) {
+func NewNodeCollector(filters ...string) (*nodeCollector, error) {
+	f := make(map[string]bool)
+	for _, filter := range filters {
+		enabled, exist := collectorState[filter]
+		if !exist {
+			return nil, fmt.Errorf("missing collector: %s", filter)
+		}
+		if !*enabled {
+			return nil, fmt.Errorf("disabled collector: %s", filter)
+		}
+		f[filter] = true
+	}
 	collectors := make(map[string]Collector)
 	for key, enabled := range collectorState {
 		if *enabled {
 			collector, err := factories[key]()
 			if err != nil {
 				return nil, err
 			}
-			collectors[key] = collector
+			if len(f) == 0 || f[key] {
+				collectors[key] = collector
+			}
 		}
 	}
 	return &nodeCollector{Collectors: collectors}, nil

node_exporter.go

@@ -14,6 +14,7 @@
 package main
 
 import (
+	"fmt"
 	"net/http"
 	_ "net/http/pprof"
 
@@ -29,6 +30,40 @@ func init() {
 	prometheus.MustRegister(version.NewCollector("node_exporter"))
 }
 
+func handler(w http.ResponseWriter, r *http.Request) {
+	filters := r.URL.Query()["collect[]"]
+	log.Debugln("collect query:", filters)
+
+	nc, err := collector.NewNodeCollector(filters...)
+	if err != nil {
+		log.Warnln("Couldn't create", err)
+		w.WriteHeader(http.StatusBadRequest)
+		w.Write([]byte(fmt.Sprintf("Couldn't create %s", err)))
+		return
+	}
+
+	registry := prometheus.NewRegistry()
+	err = registry.Register(nc)
+	if err != nil {
+		log.Errorln("Couldn't register collector:", err)
+		w.WriteHeader(http.StatusInternalServerError)
+		w.Write([]byte(fmt.Sprintf("Couldn't register collector: %s", err)))
+		return
+	}
+
+	gatherers := prometheus.Gatherers{
+		prometheus.DefaultGatherer,
+		registry,
+	}
+	// Delegate http serving to Prometheus client library, which will call collector.Collect.
+	h := promhttp.HandlerFor(gatherers,
+		promhttp.HandlerOpts{
+			ErrorLog:      log.NewErrorLogger(),
+			ErrorHandling: promhttp.ContinueOnError,
+		})
+	h.ServeHTTP(w, r)
+}
+
 func main() {
 	var (
 		listenAddress = kingpin.Flag("web.listen-address", "Address on which to expose metrics and web interface.").Default(":9100").String()
@@ -43,6 +78,7 @@ func main() {
 	log.Infoln("Starting node_exporter", version.Info())
 	log.Infoln("Build context", version.BuildContext())
 
+	// This instance is only used to check collector creation and logging.
 	nc, err := collector.NewNodeCollector()
 	if err != nil {
 		log.Fatalf("Couldn't create collector: %s", err)
@@ -52,17 +88,8 @@ func main() {
 		log.Infof(" - %s", n)
 	}
 
-	if err := prometheus.Register(nc); err != nil {
-		log.Fatalf("Couldn't register collector: %s", err)
-	}
-	handler := promhttp.HandlerFor(prometheus.DefaultGatherer,
-		promhttp.HandlerOpts{
-			ErrorLog:      log.NewErrorLogger(),
-			ErrorHandling: promhttp.ContinueOnError,
-		})
-
-	// TODO(ts): Remove deprecated and problematic InstrumentHandler usage.
-	http.Handle(*metricsPath, prometheus.InstrumentHandler("prometheus", handler))
+	// TODO(ts): Remove deprecated and problematic InstrumentHandlerFunc usage.
+	http.HandleFunc(*metricsPath, prometheus.InstrumentHandlerFunc("prometheus", handler))
 	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
 		w.Write([]byte(`<html>
 			<head><title>Node Exporter</title></head>