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prober: support adding key/value labels to probes. (#4250)

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prober: add labels to Probe instances.

This allows especially dynamically-registered probes to have a bunch
more dimensions along which they can be sliced in Prometheus.

Signed-off-by: David Anderson <danderson@tailscale.com>
This commit is contained in:
Dave Anderson
2022-03-22 13:45:11 -07:00
committed by GitHub
parent f3b13604b3
commit 0968b2d55a
2 changed files with 246 additions and 120 deletions
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prober/prober.go
+134 -64
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@@ -9,13 +9,16 @@ package prober
import (
"context"
"encoding/json"
"errors"
"expvar"
"fmt"
"io"
"log"
"sort"
"strings"
"sync"
"time"
"tailscale.com/metrics"
)
// ProbeFunc is a function that probes something and reports whether
@@ -29,33 +32,6 @@ type Prober struct {
now func() time.Time
newTicker func(time.Duration) ticker
// lastStart is the time, in seconds since epoch, of the last time
// each probe started a probe cycle.
lastStart metrics.LabelMap
// lastEnd is the time, in seconds since epoch, of the last time
// each probe finished a probe cycle.
lastEnd metrics.LabelMap
// lastResult records whether probes succeeded. A successful probe
// is recorded as 1, a failure as 0.
lastResult metrics.LabelMap
// lastLatency records how long the last probe cycle took for each
// probe, in milliseconds.
lastLatency metrics.LabelMap
// probeInterval records the time in seconds between successive
// runs of each probe.
//
// This is to help Prometheus figure out how long a probe should
// be failing before it fires an alert for it. To avoid random
// background noise, you want it to wait for more than 1
// datapoint, but you also can't use a fixed interval because some
// probes might run every few seconds, while e.g. TLS certificate
// expiry might only run once a day.
//
// So, for each probe, the prober tells Prometheus how often it
// runs, so that the alert can autotune itself to eliminate noise
// without being excessively delayed.
probeInterval metrics.LabelMap
mu sync.Mutex // protects all following fields
probes map[string]*Probe
}
@@ -67,32 +43,21 @@ func New() *Prober {
func newForTest(now func() time.Time, newTicker func(time.Duration) ticker) *Prober {
return &Prober{
now: now,
newTicker: newTicker,
lastStart: metrics.LabelMap{Label: "probe"},
lastEnd: metrics.LabelMap{Label: "probe"},
lastResult: metrics.LabelMap{Label: "probe"},
lastLatency: metrics.LabelMap{Label: "probe"},
probeInterval: metrics.LabelMap{Label: "probe"},
probes: map[string]*Probe{},
now: now,
newTicker: newTicker,
probes: map[string]*Probe{},
}
}
// Expvar returns the metrics for running probes.
func (p *Prober) Expvar() *metrics.Set {
ret := new(metrics.Set)
ret.Set("start_secs", &p.lastStart)
ret.Set("end_secs", &p.lastEnd)
ret.Set("result", &p.lastResult)
ret.Set("latency_millis", &p.lastLatency)
ret.Set("interval_secs", &p.probeInterval)
return ret
func (p *Prober) Expvar() expvar.Var {
return varExporter{p}
}
// Run executes fun every interval, and exports probe results under probeName.
//
// Registering a probe under an already-registered name panics.
func (p *Prober) Run(name string, interval time.Duration, fun ProbeFunc) *Probe {
func (p *Prober) Run(name string, interval time.Duration, labels map[string]string, fun ProbeFunc) *Probe {
p.mu.Lock()
defer p.mu.Unlock()
if _, ok := p.probes[name]; ok {
@@ -111,9 +76,9 @@ func (p *Prober) Run(name string, interval time.Duration, fun ProbeFunc) *Probe
doProbe: fun,
interval: interval,
tick: ticker,
labels: labels,
}
p.probes[name] = probe
p.probeInterval.Get(name).Set(int64(interval.Seconds()))
go probe.loop()
return probe
}
@@ -123,11 +88,6 @@ func (p *Prober) unregister(probe *Probe) {
defer p.mu.Unlock()
name := probe.name
delete(p.probes, name)
p.lastStart.Delete(name)
p.lastEnd.Delete(name)
p.lastResult.Delete(name)
p.lastLatency.Delete(name)
p.probeInterval.Delete(name)
}
// Reports the number of registered probes. For tests only.
@@ -149,6 +109,12 @@ type Probe struct {
doProbe ProbeFunc
interval time.Duration
tick ticker
labels map[string]string
mu sync.Mutex
start time.Time // last time doProbe started
end time.Time // last time doProbe returned
result bool // whether the last doProbe call succeeded
}
// Close shuts down the Probe and unregisters it from its Prober.
@@ -183,7 +149,7 @@ func (p *Probe) loop() {
// the probe either succeeds or fails before the next cycle is
// scheduled to start.
func (p *Probe) run() {
start := p.start()
start := p.recordStart()
defer func() {
// Prevent a panic within one probe function from killing the
// entire prober, so that a single buggy probe doesn't destroy
@@ -192,7 +158,7 @@ func (p *Probe) run() {
// alert for debugging.
if r := recover(); r != nil {
log.Printf("probe %s panicked: %v", p.name, r)
p.end(start, errors.New("panic"))
p.recordEnd(start, errors.New("panic"))
}
}()
timeout := time.Duration(float64(p.interval) * 0.8)
@@ -200,27 +166,131 @@ func (p *Probe) run() {
defer cancel()
err := p.doProbe(ctx)
p.end(start, err)
p.recordEnd(start, err)
if err != nil {
log.Printf("probe %s: %v", p.name, err)
}
}
func (p *Probe) start() time.Time {
func (p *Probe) recordStart() time.Time {
st := p.prober.now()
p.prober.lastStart.Get(p.name).Set(st.Unix())
p.mu.Lock()
defer p.mu.Unlock()
p.start = st
return st
}
func (p *Probe) end(start time.Time, err error) {
func (p *Probe) recordEnd(start time.Time, err error) {
end := p.prober.now()
p.prober.lastEnd.Get(p.name).Set(end.Unix())
p.prober.lastLatency.Get(p.name).Set(end.Sub(start).Milliseconds())
v := int64(1)
if err != nil {
v = 0
p.mu.Lock()
defer p.mu.Unlock()
p.end = end
p.result = err == nil
}
type varExporter struct {
p *Prober
}
// probeInfo is the state of a Probe. Used in expvar-format debug
// data.
type probeInfo struct {
Labels map[string]string
Start time.Time
End time.Time
Latency string // as a string because time.Duration doesn't encode readably to JSON
Result bool
}
// String implements expvar.Var, returning the prober's state as an
// encoded JSON map of probe name to its probeInfo.
func (v varExporter) String() string {
out := map[string]probeInfo{}
v.p.mu.Lock()
probes := make([]*Probe, 0, len(v.p.probes))
for _, probe := range v.p.probes {
probes = append(probes, probe)
}
v.p.mu.Unlock()
for _, probe := range probes {
probe.mu.Lock()
inf := probeInfo{
Labels: probe.labels,
Start: probe.start,
End: probe.end,
Result: probe.result,
}
if probe.end.After(probe.start) {
inf.Latency = probe.end.Sub(probe.start).String()
}
out[probe.name] = inf
probe.mu.Unlock()
}
bs, err := json.Marshal(out)
if err != nil {
return fmt.Sprintf(`{"error": %q}`, err)
}
return string(bs)
}
// WritePrometheus writes the the state of all probes to w.
//
// For each probe, WritePrometheus exports 5 variables:
// - <prefix>_interval_secs, how frequently the probe runs.
// - <prefix>_start_secs, when the probe last started running, in seconds since epoch.
// - <prefix>_end_secs, when the probe last finished running, in seconds since epoch.
// - <prefix>_latency_millis, how long the last probe cycle took, in
// milliseconds. This is just (end_secs-start_secs) in an easier to
// graph form.
// - <prefix>_result, 1 if the last probe succeeded, 0 if it failed.
//
// Each probe has a set of static key/value labels (defined once at
// probe creation), which are added as Prometheus metric labels to
// that probe's variables.
func (v varExporter) WritePrometheus(w io.Writer, prefix string) {
v.p.mu.Lock()
probes := make([]*Probe, 0, len(v.p.probes))
for _, probe := range v.p.probes {
probes = append(probes, probe)
}
v.p.mu.Unlock()
sort.Slice(probes, func(i, j int) bool {
return probes[i].name < probes[j].name
})
for _, probe := range probes {
probe.mu.Lock()
keys := make([]string, 0, len(probe.labels))
for k := range probe.labels {
keys = append(keys, k)
}
sort.Strings(keys)
var sb strings.Builder
fmt.Fprintf(&sb, "name=%q", probe.name)
for _, k := range keys {
fmt.Fprintf(&sb, ",%s=%q", k, probe.labels[k])
}
labels := sb.String()
fmt.Fprintf(w, "%s_interval_secs{%s} %f\n", prefix, labels, probe.interval.Seconds())
if !probe.start.IsZero() {
fmt.Fprintf(w, "%s_start_secs{%s} %d\n", prefix, labels, probe.start.Unix())
}
if !probe.end.IsZero() {
fmt.Fprintf(w, "%s_end_secs{%s} %d\n", prefix, labels, probe.end.Unix())
// Start is always present if end is.
fmt.Fprintf(w, "%s_latency_millis{%s} %d\n", prefix, labels, probe.end.Sub(probe.start).Milliseconds())
if probe.result {
fmt.Fprintf(w, "%s_result{%s} 1\n", prefix, labels)
} else {
fmt.Fprintf(w, "%s_result{%s} 0\n", prefix, labels)
}
}
probe.mu.Unlock()
}
p.prober.lastResult.Get(p.name).Set(v)
}
// ticker wraps a time.Ticker in a way that can be faked for tests.