From 159e96f6c79253cac6589cc72e5bc9acef4a08dd Mon Sep 17 00:00:00 2001 From: Bjoern Rabenstein Date: Mon, 12 Jan 2015 19:16:09 +0100 Subject: [PATCH] Allow error reporting during metrics collection and simplify Register(). Both are interface changes I want to get in before public announcement. They only break rare usage cases, and are always easy to fix, but still we want to avoid breaking changes after a wider announcement of the project. The change of Register() simply removes the return of the Collector, which nobody was using in practice. It was just bloating the call syntax. Note that this is different from RegisterOrGet(), which is used at various occasions where you want to register something that might or might not be registered already, but if it is, you want the previously registered Collector back (because that's the relevant one). WRT error reporting: I first tried the obvious way of letting the Collector methods Describe() and Collect() return error. However, I had to conclude that that bloated _many_ calls and their handling in very obnoxious ways. On the other hand, the case where you actually want to report errors during registration or collection is very rare. Hence, this approach has the wrong trade-off. The approach taken here might at first appear clunky but is in practice quite handy, mostly because there is almost no change for the "normal" case of "no special error handling", but also because it plays well with the way descriptors and metrics are handled (via channels). Explaining the approach in more detail: - During registration / describe: Error handling was actually already in place (for invalid descriptors, which carry an error anyway). I only added a convenience function to create an invalid descriptor with a given error on purpose. - Metrics are now treated in a similar way. The Write method returns an error now (the only change in interface). An "invalid metric" is provided that can be sent via the channel to signal that that metric could not be collected. It alse transports an error. NON-GOALS OF THIS COMMIT: This is NOT yet the major improvement of the whole registry part, where we want a public Registry interface and plenty of modular configurations (for error handling, various auto-metrics, http instrumentation, testing, ...). However, we can do that whole thing without breaking existing interfaces. For now (which is a significant issue) any error during collection will either cause a 500 HTTP response or a panic (depending on registry config). Later, we definitely want to have a possibility to skip (and only report somehow) non-collectible metrics instead of aborting the whole scrape. --- prometheus/collector.go | 3 +- prometheus/desc.go | 10 ++++ prometheus/example_selfcollector_test.go | 3 +- prometheus/examples_test.go | 18 +++---- prometheus/expvar.go | 62 ++++++++++++------------ prometheus/go_collector_test.go | 4 +- prometheus/metric.go | 22 ++++++++- prometheus/process_collector.go | 27 +++++++++-- prometheus/registry.go | 20 +++++--- prometheus/summary.go | 3 +- prometheus/value.go | 17 ++++--- 11 files changed, 123 insertions(+), 66 deletions(-) diff --git a/prometheus/collector.go b/prometheus/collector.go index afa0fc8..f5cb2f6 100644 --- a/prometheus/collector.go +++ b/prometheus/collector.go @@ -33,7 +33,8 @@ type Collector interface { // duplicate descriptors. Those duplicates are simply ignored. However, // two different Collectors must not send duplicate descriptors.) This // method idempotently sends the same descriptors throughout the - // lifetime of the Collector. + // lifetime of the Collector. A Collector unable to describe itself must + // send an invalid descriptor (created with NewInvalidDesc). Describe(chan<- *Desc) // Collect is called by Prometheus when collecting metrics. The // implementation sends each collected metric via the provided channel diff --git a/prometheus/desc.go b/prometheus/desc.go index b4f8652..e09f86d 100644 --- a/prometheus/desc.go +++ b/prometheus/desc.go @@ -166,6 +166,16 @@ func NewDesc(fqName, help string, variableLabels []string, constLabels Labels) * return d } +// NewInvalidDesc returns an invalid descriptor, i.e. a descriptor with the +// provided error set. If a collector returning such a descriptor is registered, +// registration will fail with the provided error. NewInvalidDesc can be used by +// a Collector to signal inability to describe itself. +func NewInvalidDesc(err error) *Desc { + return &Desc{ + err: err, + } +} + func (d *Desc) String() string { lpStrings := make([]string, 0, len(d.constLabelPairs)) for _, lp := range d.constLabelPairs { diff --git a/prometheus/example_selfcollector_test.go b/prometheus/example_selfcollector_test.go index e4fef39..1ac0791 100644 --- a/prometheus/example_selfcollector_test.go +++ b/prometheus/example_selfcollector_test.go @@ -49,8 +49,9 @@ func (cm *CallbackMetric) Desc() *prometheus.Desc { return cm.desc } -func (cm *CallbackMetric) Write(m *dto.Metric) { +func (cm *CallbackMetric) Write(m *dto.Metric) error { m.Untyped = &dto.Untyped{Value: proto.Float64(cm.callback())} + return nil } func ExampleSelfCollector() { diff --git a/prometheus/examples_test.go b/prometheus/examples_test.go index 14e853d..63261db 100644 --- a/prometheus/examples_test.go +++ b/prometheus/examples_test.go @@ -74,7 +74,7 @@ func ExampleGaugeVec() { } func ExampleGaugeFunc() { - if _, err := prometheus.Register(prometheus.NewGaugeFunc( + if err := prometheus.Register(prometheus.NewGaugeFunc( prometheus.GaugeOpts{ Subsystem: "runtime", Name: "goroutines_count", @@ -95,7 +95,7 @@ func ExampleCounter() { pushCounter := prometheus.NewCounter(prometheus.CounterOpts{ Name: "repository_pushes", // Note: No help string... }) - _, err := prometheus.Register(pushCounter) // ... so this will return an error. + err := prometheus.Register(pushCounter) // ... so this will return an error. if err != nil { fmt.Println("Push counter couldn't be registered, no counting will happen:", err) return @@ -106,7 +106,7 @@ func ExampleCounter() { Name: "repository_pushes", Help: "Number of pushes to external repository.", }) - _, err = prometheus.Register(pushCounter) + err = prometheus.Register(pushCounter) if err != nil { fmt.Println("Push counter couldn't be registered AGAIN, no counting will happen:", err) return @@ -194,7 +194,7 @@ func ExampleRegister() { Help: "Total number of tasks completed.", }) // This will register fine. - if _, err := prometheus.Register(taskCounter); err != nil { + if err := prometheus.Register(taskCounter); err != nil { fmt.Println(err) } else { fmt.Println("taskCounter registered.") @@ -219,7 +219,7 @@ func ExampleRegister() { ) // Registering will fail because we already have a metric of that name. - if _, err := prometheus.Register(taskCounterVec); err != nil { + if err := prometheus.Register(taskCounterVec); err != nil { fmt.Println("taskCounterVec not registered:", err) } else { fmt.Println("taskCounterVec registered.") @@ -231,7 +231,7 @@ func ExampleRegister() { } // Try registering taskCounterVec again. - if _, err := prometheus.Register(taskCounterVec); err != nil { + if err := prometheus.Register(taskCounterVec); err != nil { fmt.Println("taskCounterVec not registered:", err) } else { fmt.Println("taskCounterVec registered.") @@ -253,7 +253,7 @@ func ExampleRegister() { }, []string{"worker_id"}, ) - if _, err := prometheus.Register(taskCounterVec); err != nil { + if err := prometheus.Register(taskCounterVec); err != nil { fmt.Println("taskCounterVec not registered:", err) } else { fmt.Println("taskCounterVec registered.") @@ -299,7 +299,7 @@ func ExampleRegister() { ConstLabels: prometheus.Labels{"worker_id": "42"}, } taskCounterForWorker42 := prometheus.NewCounter(counterOpts) - if _, err := prometheus.Register(taskCounterForWorker42); err != nil { + if err := prometheus.Register(taskCounterForWorker42); err != nil { fmt.Println("taskCounterVForWorker42 not registered:", err) } else { fmt.Println("taskCounterForWorker42 registered.") @@ -313,7 +313,7 @@ func ExampleRegister() { // counterOpts. Just change the ConstLabels. counterOpts.ConstLabels = prometheus.Labels{"worker_id": "2001"} taskCounterForWorker2001 := prometheus.NewCounter(counterOpts) - if _, err := prometheus.Register(taskCounterForWorker2001); err != nil { + if err := prometheus.Register(taskCounterForWorker2001); err != nil { fmt.Println("taskCounterVForWorker2001 not registered:", err) } else { fmt.Println("taskCounterForWorker2001 registered.") diff --git a/prometheus/expvar.go b/prometheus/expvar.go index d964642..636d8b3 100644 --- a/prometheus/expvar.go +++ b/prometheus/expvar.go @@ -82,36 +82,38 @@ func (e *ExpvarCollector) Collect(ch chan<- Metric) { } var v interface{} labels := make([]string, len(desc.variableLabels)) - if err := json.Unmarshal([]byte(expVar.String()), &v); err == nil { - var processValue func(v interface{}, i int) - processValue = func(v interface{}, i int) { - if i >= len(labels) { - copiedLabels := append(make([]string, 0, len(labels)), labels...) - switch v := v.(type) { - case float64: - m = MustNewConstMetric(desc, UntypedValue, v, copiedLabels...) - case bool: - if v { - m = MustNewConstMetric(desc, UntypedValue, 1, copiedLabels...) - } else { - m = MustNewConstMetric(desc, UntypedValue, 0, copiedLabels...) - } - default: - return - } - ch <- m - return - } - vm, ok := v.(map[string]interface{}) - if !ok { - return - } - for lv, val := range vm { - labels[i] = lv - processValue(val, i+1) - } - } - processValue(v, 0) + if err := json.Unmarshal([]byte(expVar.String()), &v); err != nil { + ch <- NewInvalidMetric(desc, err) + continue } + var processValue func(v interface{}, i int) + processValue = func(v interface{}, i int) { + if i >= len(labels) { + copiedLabels := append(make([]string, 0, len(labels)), labels...) + switch v := v.(type) { + case float64: + m = MustNewConstMetric(desc, UntypedValue, v, copiedLabels...) + case bool: + if v { + m = MustNewConstMetric(desc, UntypedValue, 1, copiedLabels...) + } else { + m = MustNewConstMetric(desc, UntypedValue, 0, copiedLabels...) + } + default: + return + } + ch <- m + return + } + vm, ok := v.(map[string]interface{}) + if !ok { + return + } + for lv, val := range vm { + labels[i] = lv + processValue(val, i+1) + } + } + processValue(v, 0) } } diff --git a/prometheus/go_collector_test.go b/prometheus/go_collector_test.go index 60af3b5..4e7d572 100644 --- a/prometheus/go_collector_test.go +++ b/prometheus/go_collector_test.go @@ -31,7 +31,7 @@ func TestGoCollector(t *testing.T) { select { case metric := <-ch: switch m := metric.(type) { - // Attention, this als catches Counter ... + // Attention, this also catches Counter... case Gauge: pb := &dto.Metric{} m.Write(pb) @@ -43,7 +43,7 @@ func TestGoCollector(t *testing.T) { } if diff := int(pb.GetGauge().GetValue()) - old; diff != 1 { - t.Errorf("want 1 new goroutine, got %f", diff) + t.Errorf("want 1 new goroutine, got %d", diff) } return diff --git a/prometheus/metric.go b/prometheus/metric.go index b199210..115331f 100644 --- a/prometheus/metric.go +++ b/prometheus/metric.go @@ -27,7 +27,9 @@ import ( type Metric interface { // Desc returns the descriptor for the Metric. This method idempotently // returns the same descriptor throughout the lifetime of the - // Metric. The returned descriptor is immutable by contract. + // Metric. The returned descriptor is immutable by contract. A Metric + // unable to describe itself must return an invalid descriptor (created + // with NewInvalidDesc). Desc() *Desc // Write encodes the Metric into a "Metric" Protocol Buffer data // transmission object. @@ -46,7 +48,7 @@ type Metric interface { // // While populating dto.Metric, labels must be sorted lexicographically. // (Implementers may find LabelPairSorter useful for that.) - Write(*dto.Metric) + Write(*dto.Metric) error } // Opts bundles the options for creating most Metric types. Each metric @@ -144,3 +146,19 @@ func (s hashSorter) Swap(i, j int) { func (s hashSorter) Less(i, j int) bool { return s[i] < s[j] } + +type invalidMetric struct { + desc *Desc + err error +} + +// NewInvalidMetric returns a metric whose Write method always returns the +// provided error. It is useful if a Collector finds itself unable to collect +// a metric and wishes to report an error to the registry. +func NewInvalidMetric(desc *Desc, err error) Metric { + return &invalidMetric{desc, err} +} + +func (m *invalidMetric) Desc() *Desc { return m.desc } + +func (m *invalidMetric) Write(*dto.Metric) error { return m.err } diff --git a/prometheus/process_collector.go b/prometheus/process_collector.go index 60c5912..567d88c 100644 --- a/prometheus/process_collector.go +++ b/prometheus/process_collector.go @@ -92,10 +92,23 @@ func noopCollect(ch chan<- Metric) {} func (c *processCollector) procfsCollect(ch chan<- Metric) { p, err := procfs.NewProc(c.pidFn()) if err != nil { + // Report collect errors for all metrics. + ch <- NewInvalidMetric(c.cpuTotal.Desc(), err) + ch <- NewInvalidMetric(c.openFDs.Desc(), err) + ch <- NewInvalidMetric(c.maxFDs.Desc(), err) + ch <- NewInvalidMetric(c.vsize.Desc(), err) + ch <- NewInvalidMetric(c.rss.Desc(), err) + ch <- NewInvalidMetric(c.startTime.Desc(), err) return } - if stat, err := p.NewStat(); err == nil { + if stat, err := p.NewStat(); err != nil { + // Report collect errors for metrics depending on stat. + ch <- NewInvalidMetric(c.vsize.Desc(), err) + ch <- NewInvalidMetric(c.rss.Desc(), err) + ch <- NewInvalidMetric(c.startTime.Desc(), err) + ch <- NewInvalidMetric(c.cpuTotal.Desc(), err) + } else { c.cpuTotal.Set(stat.CPUTime()) ch <- c.cpuTotal c.vsize.Set(float64(stat.VirtualMemory())) @@ -103,18 +116,24 @@ func (c *processCollector) procfsCollect(ch chan<- Metric) { c.rss.Set(float64(stat.ResidentMemory())) ch <- c.rss - if startTime, err := stat.StartTime(); err == nil { + if startTime, err := stat.StartTime(); err != nil { + ch <- NewInvalidMetric(c.startTime.Desc(), err) + } else { c.startTime.Set(startTime) ch <- c.startTime } } - if fds, err := p.FileDescriptorsLen(); err == nil { + if fds, err := p.FileDescriptorsLen(); err != nil { + ch <- NewInvalidMetric(c.openFDs.Desc(), err) + } else { c.openFDs.Set(float64(fds)) ch <- c.openFDs } - if limits, err := p.NewLimits(); err == nil { + if limits, err := p.NewLimits(); err != nil { + ch <- NewInvalidMetric(c.maxFDs.Desc(), err) + } else { c.maxFDs.Set(float64(limits.OpenFiles)) ch <- c.maxFDs } diff --git a/prometheus/registry.go b/prometheus/registry.go index 81eda27..551fb92 100644 --- a/prometheus/registry.go +++ b/prometheus/registry.go @@ -105,24 +105,23 @@ func UninstrumentedHandler() http.Handler { // returns an error if the descriptors provided by the Collector are invalid or // if they - in combination with descriptors of already registered Collectors - // do not fulfill the consistency and uniqueness criteria described in the Desc -// documentation. If the registration is successful, the registered Collector -// is returned. +// documentation. // // Do not register the same Collector multiple times concurrently. (Registering // the same Collector twice would result in an error anyway, but on top of that, // it is not safe to do so concurrently.) -func Register(m Collector) (Collector, error) { - return defRegistry.Register(m) +func Register(m Collector) error { + _, err := defRegistry.Register(m) + return err } // MustRegister works like Register but panics where Register would have // returned an error. -func MustRegister(m Collector) Collector { - m, err := Register(m) +func MustRegister(m Collector) { + err := Register(m) if err != nil { panic(err) } - return m } // RegisterOrGet works like Register but does not return an error if a Collector @@ -447,7 +446,12 @@ func (r *registry) writePB(w io.Writer, writeEncoded encoder) (int, error) { } dtoMetric := r.getMetric() defer r.giveMetric(dtoMetric) - metric.Write(dtoMetric) + if err := metric.Write(dtoMetric); err != nil { + // TODO: Consider different means of error reporting so + // that a single erroneous metric could be skipped + // instead of blowing up the whole collection. + return 0, fmt.Errorf("error collecting metric %v: %s", desc, err) + } switch { case metricFamily.Type != nil: // Type already set. We are good. diff --git a/prometheus/summary.go b/prometheus/summary.go index 93d4320..afb9bca 100644 --- a/prometheus/summary.go +++ b/prometheus/summary.go @@ -242,7 +242,7 @@ func (s *summary) Observe(v float64) { } } -func (s *summary) Write(out *dto.Metric) { +func (s *summary) Write(out *dto.Metric) error { sum := &dto.Summary{} qs := make([]*dto.Quantile, 0, len(s.objectives)) @@ -277,6 +277,7 @@ func (s *summary) Write(out *dto.Metric) { out.Summary = sum out.Label = s.labelPairs + return nil } func (s *summary) newStream() *quantile.Stream { diff --git a/prometheus/value.go b/prometheus/value.go index 70af308..b34f863 100644 --- a/prometheus/value.go +++ b/prometheus/value.go @@ -98,12 +98,12 @@ func (v *value) Sub(val float64) { v.Add(val * -1) } -func (v *value) Write(out *dto.Metric) { +func (v *value) Write(out *dto.Metric) error { v.mtx.RLock() val := v.val v.mtx.RUnlock() - populateMetric(v.valType, val, v.labelPairs, out) + return populateMetric(v.valType, val, v.labelPairs, out) } // valueFunc is a generic metric for simple values retrieved on collect time @@ -141,8 +141,8 @@ func (v *valueFunc) Desc() *Desc { return v.desc } -func (v *valueFunc) Write(out *dto.Metric) { - populateMetric(v.valType, v.function(), v.labelPairs, out) +func (v *valueFunc) Write(out *dto.Metric) error { + return populateMetric(v.valType, v.function(), v.labelPairs, out) } // NewConstMetric returns a metric with one fixed value that cannot be @@ -184,8 +184,8 @@ func (m *constMetric) Desc() *Desc { return m.desc } -func (m *constMetric) Write(out *dto.Metric) { - populateMetric(m.valType, m.val, m.labelPairs, out) +func (m *constMetric) Write(out *dto.Metric) error { + return populateMetric(m.valType, m.val, m.labelPairs, out) } func populateMetric( @@ -193,7 +193,7 @@ func populateMetric( v float64, labelPairs []*dto.LabelPair, m *dto.Metric, -) { +) error { m.Label = labelPairs switch t { case CounterValue: @@ -203,8 +203,9 @@ func populateMetric( case UntypedValue: m.Untyped = &dto.Untyped{Value: proto.Float64(v)} default: - panic(fmt.Errorf("encountered unknown type %v", t)) + return fmt.Errorf("encountered unknown type %v", t) } + return nil } func makeLabelPairs(desc *Desc, labelValues []string) []*dto.LabelPair {