Don't count empty collection as success (#1613)

Many collectors depend on underlying features to be enabled. This causes
confusion about what "success" means. This changes the behavior of the
`node_scrape_collector_success` metric.

* When a collector is unable to find data don't return success.
* Catch the no data error and send to Debug log level to avoid log spam.
* Update collectors to support this new functionality.
* Fix copy-pasta mistake in infiband debug message.

Closes: https://github.com/prometheus/node_exporter/issues/1323

Signed-off-by: Ben Kochie <superq@gmail.com>

10 files changed, 24 insertions, 12 deletions

diff --git a/collector/bonding_linux.go b/collector/bonding_linux.go
index 771786b..78e94b2 100644
--- a/collector/bonding_linux.go
+++ b/collector/bonding_linux.go
@@ -61,7 +61,7 @@ func (c *bondingCollector) Update(ch chan<- prometheus.Metric) error {
         if err != nil {
                 if os.IsNotExist(err) {
                         level.Debug(c.logger).Log("msg", "Not collecting bonding, file does not exist", "file", statusfile)
-                        return nil
+                        return ErrNoData
                 }
                 return err
         }
diff --git a/collector/collector.go b/collector/collector.go
index af8712c..0fec09c 100644
--- a/collector/collector.go
+++ b/collector/collector.go
@@ -15,6 +15,7 @@
 package collector
 
 import (
+        "errors"
         "fmt"
         "sync"
         "time"
@@ -131,7 +132,11 @@ func execute(name string, c Collector, ch chan<- prometheus.Metric, logger log.L
         var success float64
 
         if err != nil {
-                level.Error(logger).Log("msg", "collector failed", "name", name, "duration_seconds", duration.Seconds(), "err", err)
+                if IsNoDataError(err) {
+                        level.Debug(logger).Log("msg", "collector returned no data", "name", name, "duration_seconds", duration.Seconds(), "err", err)
+                } else {
+                        level.Error(logger).Log("msg", "collector failed", "name", name, "duration_seconds", duration.Seconds(), "err", err)
+                }
                 success = 0
         } else {
                 level.Debug(logger).Log("msg", "collector succeeded", "name", name, "duration_seconds", duration.Seconds())
@@ -155,3 +160,10 @@ type typedDesc struct {
 func (d *typedDesc) mustNewConstMetric(value float64, labels ...string) prometheus.Metric {
         return prometheus.MustNewConstMetric(d.desc, d.valueType, value, labels...)
 }
+
+// ErrNoData indicates the collector found no data to collect, but had no other error.
+var ErrNoData = errors.New("collector returned no data")
+
+func IsNoDataError(err error) bool {
+        return err == ErrNoData
+}
diff --git a/collector/drbd_linux.go b/collector/drbd_linux.go
index 5a340b9..6815c5f 100644
--- a/collector/drbd_linux.go
+++ b/collector/drbd_linux.go
@@ -188,7 +188,7 @@ func (c *drbdCollector) Update(ch chan<- prometheus.Metric) error {
         if err != nil {
                 if os.IsNotExist(err) {
                         level.Debug(c.logger).Log("msg", "stats file does not exist, skipping", "file", statsFile, "err", err)
-                        return nil
+                        return ErrNoData
                 }
 
                 return err
diff --git a/collector/hwmon_linux.go b/collector/hwmon_linux.go
index 31dbd22..5649942 100644
--- a/collector/hwmon_linux.go
+++ b/collector/hwmon_linux.go
@@ -426,7 +426,7 @@ func (c *hwMonCollector) Update(ch chan<- prometheus.Metric) error {
         if err != nil {
                 if os.IsNotExist(err) {
                         level.Debug(c.logger).Log("msg", "hwmon collector metrics are not available for this system")
-                        return nil
+                        return ErrNoData
                 }
 
                 return err
diff --git a/collector/infiniband_linux.go b/collector/infiniband_linux.go
index 4fa68ba..1f453b8 100644
--- a/collector/infiniband_linux.go
+++ b/collector/infiniband_linux.go
@@ -109,8 +109,8 @@ func (c *infinibandCollector) Update(ch chan<- prometheus.Metric) error {
         devices, err := c.fs.InfiniBandClass()
         if err != nil {
                 if os.IsNotExist(err) {
-                        level.Debug(c.logger).Log("msg", "IPv4 sockstat statistics not found, skipping")
-                        return nil
+                        level.Debug(c.logger).Log("msg", "infiniband statistics not found, skipping")
+                        return ErrNoData
                 }
                 return fmt.Errorf("error obtaining InfiniBand class info: %s", err)
         }
diff --git a/collector/ipvs_linux.go b/collector/ipvs_linux.go
index 89469e5..11adf0f 100644
--- a/collector/ipvs_linux.go
+++ b/collector/ipvs_linux.go
@@ -115,7 +115,7 @@ func (c *ipvsCollector) Update(ch chan<- prometheus.Metric) error {
                 // Cannot access ipvs metrics, report no error.
                 if os.IsNotExist(err) {
                         level.Debug(c.logger).Log("msg", "ipvs collector metrics are not available for this system")
-                        return nil
+                        return ErrNoData
                 }
                 return fmt.Errorf("could not get IPVS stats: %s", err)
         }
diff --git a/collector/mdadm_linux.go b/collector/mdadm_linux.go
index faf1cee..05f83ee 100644
--- a/collector/mdadm_linux.go
+++ b/collector/mdadm_linux.go
@@ -105,7 +105,7 @@ func (c *mdadmCollector) Update(ch chan<- prometheus.Metric) error {
         if err != nil {
                 if os.IsNotExist(err) {
                         level.Debug(c.logger).Log("msg", "Not collecting mdstat, file does not exist", "file", *procPath)
-                        return nil
+                        return ErrNoData
                 }
 
                 return fmt.Errorf("error parsing mdstatus: %s", err)
diff --git a/collector/nfs_linux.go b/collector/nfs_linux.go
index 7ed4930..55f9e19 100644
--- a/collector/nfs_linux.go
+++ b/collector/nfs_linux.go
@@ -97,7 +97,7 @@ func (c *nfsCollector) Update(ch chan<- prometheus.Metric) error {
         if err != nil {
                 if os.IsNotExist(err) {
                         level.Debug(c.logger).Log("msg", "Not collecting NFS metrics", "err", err)
-                        return nil
+                        return ErrNoData
                 }
                 return fmt.Errorf("failed to retrieve nfs stats: %w", err)
         }
diff --git a/collector/nfsd_linux.go b/collector/nfsd_linux.go
index 234e1da..b6f2f8e 100644
--- a/collector/nfsd_linux.go
+++ b/collector/nfsd_linux.go
@@ -63,7 +63,7 @@ func (c *nfsdCollector) Update(ch chan<- prometheus.Metric) error {
         if err != nil {
                 if os.IsNotExist(err) {
                         level.Debug(c.logger).Log("msg", "Not collecting NFSd metrics", "err", err)
-                        return nil
+                        return ErrNoData
                 }
                 return fmt.Errorf("failed to retrieve nfsd stats: %w", err)
         }
diff --git a/collector/wifi_linux.go b/collector/wifi_linux.go
index 5a5a86c..118e714 100644
--- a/collector/wifi_linux.go
+++ b/collector/wifi_linux.go
@@ -167,11 +167,11 @@ func (c *wifiCollector) Update(ch chan<- prometheus.Metric) error {
                 // Cannot access wifi metrics, report no error.
                 if os.IsNotExist(err) {
                         level.Debug(c.logger).Log("msg", "wifi collector metrics are not available for this system")
-                        return nil
+                        return ErrNoData
                 }
                 if os.IsPermission(err) {
                         level.Debug(c.logger).Log("msg", "wifi collector got permission denied when accessing metrics")
-                        return nil
+                        return ErrNoData
                 }
 
                 return fmt.Errorf("failed to access wifi data: %w", err)