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Merge pull request #594 from prometheus/beorn7/promhttp 

Add an error counter for internal errors in the HTTP handler
This commit is contained in:
Björn Rabenstein 2019-06-06 17:41:52 +02:00 committed by GitHub
parent ea8c935f20 4d8144c11a
commit 7ed96b33bd
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
2 changed files with 70 additions and 8 deletions
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47
prometheus/promhttp/http.go
View File

@ -84,10 +84,32 @@ func Handler() http.Handler {
// instrumentation. Use the InstrumentMetricHandler function to apply the same
// kind of instrumentation as it is used by the Handler function.
func HandlerFor(reg prometheus.Gatherer, opts HandlerOpts) http.Handler {
var inFlightSem chan struct{}
var (
inFlightSem chan struct{}
errCnt = prometheus.NewCounterVec(
prometheus.CounterOpts{
Name: "promhttp_metric_handler_errors_total",
Help: "Total number of internal errors encountered by the promhttp metric handler.",
},
[]string{"cause"},
)
)
if opts.MaxRequestsInFlight > 0 {
inFlightSem = make(chan struct{}, opts.MaxRequestsInFlight)
}
if opts.Registry != nil {
// Initialize all possibilites that can occur below.
errCnt.WithLabelValues("gathering")
errCnt.WithLabelValues("encoding")
if err := opts.Registry.Register(errCnt); err != nil {
if are, ok := err.(prometheus.AlreadyRegisteredError); ok {
errCnt = are.ExistingCollector.(*prometheus.CounterVec)
} else {
panic(err)
}
}
}
h := http.HandlerFunc(func(rsp http.ResponseWriter, req *http.Request) {
if inFlightSem != nil {
@ -106,6 +128,7 @@ func HandlerFor(reg prometheus.Gatherer, opts HandlerOpts) http.Handler {
if opts.ErrorLog != nil {
opts.ErrorLog.Println("error gathering metrics:", err)
}
errCnt.WithLabelValues("gathering").Inc()
switch opts.ErrorHandling {
case PanicOnError:
panic(err)
@ -146,6 +169,7 @@ func HandlerFor(reg prometheus.Gatherer, opts HandlerOpts) http.Handler {
if opts.ErrorLog != nil {
opts.ErrorLog.Println("error encoding and sending metric family:", err)
}
errCnt.WithLabelValues("encoding").Inc()
switch opts.ErrorHandling {
case PanicOnError:
panic(err)
@ -236,9 +260,12 @@ const (
// Ignore errors and try to serve as many metrics as possible. However,
// if no metrics can be served, serve an HTTP status code 500 and the
// last error message in the body. Only use this in deliberate "best
// effort" metrics collection scenarios. It is recommended to at least
// log errors (by providing an ErrorLog in HandlerOpts) to not mask
// errors completely.
// effort" metrics collection scenarios. In this case, it is highly
// recommended to provide other means of detecting errors: By setting an
// ErrorLog in HandlerOpts, the errors are logged. By providing a
// Registry in HandlerOpts, the exposed metrics include an error counter
// "promhttp_metric_handler_errors_total", which can be used for
// alerts.
ContinueOnError
// Panic upon the first error encountered (useful for "crash only" apps).
PanicOnError
@ -261,6 +288,18 @@ type HandlerOpts struct {
// logged regardless of the configured ErrorHandling provided ErrorLog
// is not nil.
ErrorHandling HandlerErrorHandling
// If Registry is not nil, it is used to register a metric
// "promhttp_metric_handler_errors_total", partitioned by "cause". A
// failed registration causes a panic. Note that this error counter is
// different from the instrumentation you get from the various
// InstrumentHandler... helpers. It counts errors that don't necessarily
// result in a non-2xx HTTP status code. There are two typical cases:
// (1) Encoding errors that only happen after streaming of the HTTP body
// has already started (and the status code 200 has been sent). This
// should only happen with custom collectors. (2) Collection errors with
// no effect on the HTTP status code because ErrorHandling is set to
// ContinueOnError.
Registry prometheus.Registerer
// If DisableCompression is true, the handler will never compress the
// response, even if requested by the client.
DisableCompression bool

31
prometheus/promhttp/http_test.go
View File

@ -59,7 +59,8 @@ func (b blockingCollector) Collect(ch chan<- prometheus.Metric) {
func TestHandlerErrorHandling(t *testing.T) {
// Create a registry that collects a MetricFamily with two elements,
// another with one, and reports an error.
// another with one, and reports an error. Further down, we'll use the
// same registry in the HandlerOpts.
reg := prometheus.NewRegistry()
cnt := prometheus.NewCounter(prometheus.CounterOpts{
@ -92,14 +93,17 @@ func TestHandlerErrorHandling(t *testing.T) {
errorHandler := HandlerFor(reg, HandlerOpts{
ErrorLog: logger,
ErrorHandling: HTTPErrorOnError,
Registry: reg,
})
continueHandler := HandlerFor(reg, HandlerOpts{
ErrorLog: logger,
ErrorHandling: ContinueOnError,
Registry: reg,
})
panicHandler := HandlerFor(reg, HandlerOpts{
ErrorLog: logger,
ErrorHandling: PanicOnError,
Registry: reg,
})
wantMsg := `error gathering metrics: error collecting metric Desc{fqName: "invalid_metric", help: "not helpful", constLabels: {}, variableLabels: []}: collect error
`
@ -107,10 +111,29 @@ func TestHandlerErrorHandling(t *testing.T) {
error collecting metric Desc{fqName: "invalid_metric", help: "not helpful", constLabels: {}, variableLabels: []}: collect error
`
wantOKBody := `# HELP name docstring
wantOKBody1 := `# HELP name docstring
# TYPE name counter
name{constname="constvalue",labelname="val1"} 1
name{constname="constvalue",labelname="val2"} 1
# HELP promhttp_metric_handler_errors_total Total number of internal errors encountered by the promhttp metric handler.
# TYPE promhttp_metric_handler_errors_total counter
promhttp_metric_handler_errors_total{cause="encoding"} 0
promhttp_metric_handler_errors_total{cause="gathering"} 1
# HELP the_count Ah-ah-ah! Thunder and lightning!
# TYPE the_count counter
the_count 0
`
// It might happen that counting the gathering error makes it to the
// promhttp_metric_handler_errors_total counter before it is gathered
// itself. Thus, we have to bodies that are acceptable for the test.
wantOKBody2 := `# HELP name docstring
# TYPE name counter
name{constname="constvalue",labelname="val1"} 1
name{constname="constvalue",labelname="val2"} 1
# HELP promhttp_metric_handler_errors_total Total number of internal errors encountered by the promhttp metric handler.
# TYPE promhttp_metric_handler_errors_total counter
promhttp_metric_handler_errors_total{cause="encoding"} 0
promhttp_metric_handler_errors_total{cause="gathering"} 2
# HELP the_count Ah-ah-ah! Thunder and lightning!
# TYPE the_count counter
the_count 0
@ -137,8 +160,8 @@ the_count 0
if got := logBuf.String(); got != wantMsg {
t.Errorf("got log message %q, want %q", got, wantMsg)
}
if got := writer.Body.String(); got != wantOKBody {
t.Errorf("got body %q, want %q", got, wantOKBody)
if got := writer.Body.String(); got != wantOKBody1 && got != wantOKBody2 {
t.Errorf("got body %q, want either %q or %q", got, wantOKBody1, wantOKBody2)
}
defer func() {