func ExampleCounter() {
pushCounter := prometheus.NewCounter(prometheus.CounterOpts{
Name: "repository_pushes", // Note: No help string...
})
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
}
// Try it once more, this time with a help string.
pushCounter = prometheus.NewCounter(prometheus.CounterOpts{
Name: "repository_pushes",
Help: "Number of pushes to external repository.",
})
err = prometheus.Register(pushCounter)
if err != nil {
fmt.Println("Push counter couldn't be registered AGAIN, no counting will happen:", err)
return
}
pushComplete := make(chan struct{})
// TODO: Start a goroutine that performs repository pushes and reports
// each completion via the channel.
for _ = range pushComplete {
pushCounter.Inc()
}
// Output:
// Push counter couldn't be registered, no counting will happen: descriptor Desc{fqName: "repository_pushes", help: "", constLabels: {}, variableLabels: []} is invalid: empty help string
}
func ExampleRegister() {
// Imagine you have a worker pool and want to count the tasks completed.
taskCounter := prometheus.NewCounter(prometheus.CounterOpts{
Subsystem: "worker_pool",
Name: "completed_tasks_total",
Help: "Total number of tasks completed.",
})
// This will register fine.
if err := prometheus.Register(taskCounter); err != nil {
fmt.Println(err)
} else {
fmt.Println("taskCounter registered.")
}
// Don't forget to tell the HTTP server about the Prometheus handler.
// (In a real program, you still need to start the HTTP server...)
http.Handle("/metrics", prometheus.Handler())
// Now you can start workers and give every one of them a pointer to
// taskCounter and let it increment it whenever it completes a task.
taskCounter.Inc() // This has to happen somewhere in the worker code.
// But wait, you want to see how individual workers perform. So you need
// a vector of counters, with one element for each worker.
taskCounterVec := prometheus.NewCounterVec(
prometheus.CounterOpts{
Subsystem: "worker_pool",
Name: "completed_tasks_total",
Help: "Total number of tasks completed.",
},
[]string{"worker_id"},
)
// Registering will fail because we already have a metric of that name.
if err := prometheus.Register(taskCounterVec); err != nil {
fmt.Println("taskCounterVec not registered:", err)
} else {
fmt.Println("taskCounterVec registered.")
}
// To fix, first unregister the old taskCounter.
if prometheus.Unregister(taskCounter) {
fmt.Println("taskCounter unregistered.")
}
// Try registering taskCounterVec again.
if err := prometheus.Register(taskCounterVec); err != nil {
fmt.Println("taskCounterVec not registered:", err)
} else {
fmt.Println("taskCounterVec registered.")
}
// Bummer! Still doesn't work.
// Prometheus will not allow you to ever export metrics with
// inconsistent help strings or label names. After unregistering, the
// unregistered metrics will cease to show up in the /metrics HTTP
// response, but the registry still remembers that those metrics had
// been exported before. For this example, we will now choose a
// different name. (In a real program, you would obviously not export
// the obsolete metric in the first place.)
taskCounterVec = prometheus.NewCounterVec(
prometheus.CounterOpts{
Subsystem: "worker_pool",
Name: "completed_tasks_by_id",
Help: "Total number of tasks completed.",
},
[]string{"worker_id"},
)
if err := prometheus.Register(taskCounterVec); err != nil {
fmt.Println("taskCounterVec not registered:", err)
} else {
fmt.Println("taskCounterVec registered.")
}
// Finally it worked!
// The workers have to tell taskCounterVec their id to increment the
// right element in the metric vector.
taskCounterVec.WithLabelValues("42").Inc() // Code from worker 42.
// Each worker could also keep a reference to their own counter element
// around. Pick the counter at initialization time of the worker.
myCounter := taskCounterVec.WithLabelValues("42") // From worker 42 initialization code.
myCounter.Inc() // Somewhere in the code of that worker.
// Note that something like WithLabelValues("42", "spurious arg") would
// panic (because you have provided too many label values). If you want
// to get an error instead, use GetMetricWithLabelValues(...) instead.
notMyCounter, err := taskCounterVec.GetMetricWithLabelValues("42", "spurious arg")
if err != nil {
fmt.Println("Worker initialization failed:", err)
}
if notMyCounter == nil {
fmt.Println("notMyCounter is nil.")
}
// A different (and somewhat tricky) approach is to use
// ConstLabels. ConstLabels are pairs of label names and label values
// that never change. You might ask what those labels are good for (and
// rightfully so - if they never change, they could as well be part of
// the metric name). There are essentially two use-cases: The first is
// if labels are constant throughout the lifetime of a binary execution,
// but they vary over time or between different instances of a running
// binary. The second is what we have here: Each worker creates and
// registers an own Counter instance where the only difference is in the
// value of the ConstLabels. Those Counters can all be registered
// because the different ConstLabel values guarantee that each worker
// will increment a different Counter metric.
counterOpts := prometheus.CounterOpts{
Subsystem: "worker_pool",
Name: "completed_tasks",
Help: "Total number of tasks completed.",
ConstLabels: prometheus.Labels{"worker_id": "42"},
}
taskCounterForWorker42 := prometheus.NewCounter(counterOpts)
if err := prometheus.Register(taskCounterForWorker42); err != nil {
fmt.Println("taskCounterVForWorker42 not registered:", err)
} else {
fmt.Println("taskCounterForWorker42 registered.")
}
// Obviously, in real code, taskCounterForWorker42 would be a member
// variable of a worker struct, and the "42" would be retrieved with a
// GetId() method or something. The Counter would be created and
// registered in the initialization code of the worker.
// For the creation of the next Counter, we can recycle
// counterOpts. Just change the ConstLabels.
counterOpts.ConstLabels = prometheus.Labels{"worker_id": "2001"}
taskCounterForWorker2001 := prometheus.NewCounter(counterOpts)
if err := prometheus.Register(taskCounterForWorker2001); err != nil {
fmt.Println("taskCounterVForWorker2001 not registered:", err)
} else {
fmt.Println("taskCounterForWorker2001 registered.")
}
taskCounterForWorker2001.Inc()
taskCounterForWorker42.Inc()
taskCounterForWorker2001.Inc()
// Yet another approach would be to turn the workers themselves into
// Collectors and register them. See the Collector example for details.
// Output:
// taskCounter registered.
// taskCounterVec not registered: a previously registered descriptor with the same fully-qualified name as Desc{fqName: "worker_pool_completed_tasks_total", help: "Total number of tasks completed.", constLabels: {}, variableLabels: [worker_id]} has different label names or a different help string
// taskCounter unregistered.
// taskCounterVec not registered: a previously registered descriptor with the same fully-qualified name as Desc{fqName: "worker_pool_completed_tasks_total", help: "Total number of tasks completed.", constLabels: {}, variableLabels: [worker_id]} has different label names or a different help string
// taskCounterVec registered.
// Worker initialization failed: inconsistent label cardinality
// notMyCounter is nil.
// taskCounterForWorker42 registered.
// taskCounterForWorker2001 registered.
}