| // Copyright 2016 The Prometheus Authors |
| // Licensed under the Apache License, Version 2.0 (the "License"); |
| // you may not use this file except in compliance with the License. |
| // You may obtain a copy of the License at |
| // |
| // http://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS IS" BASIS, |
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| // See the License for the specific language governing permissions and |
| // limitations under the License. |
| |
| // Package promhttp provides tooling around HTTP servers and clients. |
| // |
| // First, the package allows the creation of http.Handler instances to expose |
| // Prometheus metrics via HTTP. promhttp.Handler acts on the |
| // prometheus.DefaultGatherer. With HandlerFor, you can create a handler for a |
| // custom registry or anything that implements the Gatherer interface. It also |
| // allows the creation of handlers that act differently on errors or allow to |
| // log errors. |
| // |
| // Second, the package provides tooling to instrument instances of http.Handler |
| // via middleware. Middleware wrappers follow the naming scheme |
| // InstrumentHandlerX, where X describes the intended use of the middleware. |
| // See each function's doc comment for specific details. |
| // |
| // Finally, the package allows for an http.RoundTripper to be instrumented via |
| // middleware. Middleware wrappers follow the naming scheme |
| // InstrumentRoundTripperX, where X describes the intended use of the |
| // middleware. See each function's doc comment for specific details. |
| package promhttp |
| |
| import ( |
| "compress/gzip" |
| "fmt" |
| "io" |
| "net/http" |
| "strings" |
| "sync" |
| "time" |
| |
| "github.com/prometheus/common/expfmt" |
| |
| "github.com/prometheus/client_golang/prometheus" |
| ) |
| |
| const ( |
| contentTypeHeader = "Content-Type" |
| contentEncodingHeader = "Content-Encoding" |
| acceptEncodingHeader = "Accept-Encoding" |
| ) |
| |
| var gzipPool = sync.Pool{ |
| New: func() interface{} { |
| return gzip.NewWriter(nil) |
| }, |
| } |
| |
| // Handler returns an http.Handler for the prometheus.DefaultGatherer, using |
| // default HandlerOpts, i.e. it reports the first error as an HTTP error, it has |
| // no error logging, and it applies compression if requested by the client. |
| // |
| // The returned http.Handler is already instrumented using the |
| // InstrumentMetricHandler function and the prometheus.DefaultRegisterer. If you |
| // create multiple http.Handlers by separate calls of the Handler function, the |
| // metrics used for instrumentation will be shared between them, providing |
| // global scrape counts. |
| // |
| // This function is meant to cover the bulk of basic use cases. If you are doing |
| // anything that requires more customization (including using a non-default |
| // Gatherer, different instrumentation, and non-default HandlerOpts), use the |
| // HandlerFor function. See there for details. |
| func Handler() http.Handler { |
| return InstrumentMetricHandler( |
| prometheus.DefaultRegisterer, HandlerFor(prometheus.DefaultGatherer, HandlerOpts{}), |
| ) |
| } |
| |
| // HandlerFor returns an uninstrumented http.Handler for the provided |
| // Gatherer. The behavior of the Handler is defined by the provided |
| // HandlerOpts. Thus, HandlerFor is useful to create http.Handlers for custom |
| // Gatherers, with non-default HandlerOpts, and/or with custom (or no) |
| // 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{} |
| 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 { |
| select { |
| case inFlightSem <- struct{}{}: // All good, carry on. |
| defer func() { <-inFlightSem }() |
| default: |
| http.Error(rsp, fmt.Sprintf( |
| "Limit of concurrent requests reached (%d), try again later.", opts.MaxRequestsInFlight, |
| ), http.StatusServiceUnavailable) |
| return |
| } |
| } |
| mfs, err := reg.Gather() |
| if err != nil { |
| if opts.ErrorLog != nil { |
| opts.ErrorLog.Println("error gathering metrics:", err) |
| } |
| errCnt.WithLabelValues("gathering").Inc() |
| switch opts.ErrorHandling { |
| case PanicOnError: |
| panic(err) |
| case ContinueOnError: |
| if len(mfs) == 0 { |
| // Still report the error if no metrics have been gathered. |
| httpError(rsp, err) |
| return |
| } |
| case HTTPErrorOnError: |
| httpError(rsp, err) |
| return |
| } |
| } |
| |
| contentType := expfmt.Negotiate(req.Header) |
| header := rsp.Header() |
| header.Set(contentTypeHeader, string(contentType)) |
| |
| w := io.Writer(rsp) |
| if !opts.DisableCompression && gzipAccepted(req.Header) { |
| header.Set(contentEncodingHeader, "gzip") |
| gz := gzipPool.Get().(*gzip.Writer) |
| defer gzipPool.Put(gz) |
| |
| gz.Reset(w) |
| defer gz.Close() |
| |
| w = gz |
| } |
| |
| enc := expfmt.NewEncoder(w, contentType) |
| |
| var lastErr error |
| for _, mf := range mfs { |
| if err := enc.Encode(mf); err != nil { |
| lastErr = err |
| 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) |
| case ContinueOnError: |
| // Handled later. |
| case HTTPErrorOnError: |
| httpError(rsp, err) |
| return |
| } |
| } |
| } |
| |
| if lastErr != nil { |
| httpError(rsp, lastErr) |
| } |
| }) |
| |
| if opts.Timeout <= 0 { |
| return h |
| } |
| return http.TimeoutHandler(h, opts.Timeout, fmt.Sprintf( |
| "Exceeded configured timeout of %v.\n", |
| opts.Timeout, |
| )) |
| } |
| |
| // InstrumentMetricHandler is usually used with an http.Handler returned by the |
| // HandlerFor function. It instruments the provided http.Handler with two |
| // metrics: A counter vector "promhttp_metric_handler_requests_total" to count |
| // scrapes partitioned by HTTP status code, and a gauge |
| // "promhttp_metric_handler_requests_in_flight" to track the number of |
| // simultaneous scrapes. This function idempotently registers collectors for |
| // both metrics with the provided Registerer. It panics if the registration |
| // fails. The provided metrics are useful to see how many scrapes hit the |
| // monitored target (which could be from different Prometheus servers or other |
| // scrapers), and how often they overlap (which would result in more than one |
| // scrape in flight at the same time). Note that the scrapes-in-flight gauge |
| // will contain the scrape by which it is exposed, while the scrape counter will |
| // only get incremented after the scrape is complete (as only then the status |
| // code is known). For tracking scrape durations, use the |
| // "scrape_duration_seconds" gauge created by the Prometheus server upon each |
| // scrape. |
| func InstrumentMetricHandler(reg prometheus.Registerer, handler http.Handler) http.Handler { |
| cnt := prometheus.NewCounterVec( |
| prometheus.CounterOpts{ |
| Name: "promhttp_metric_handler_requests_total", |
| Help: "Total number of scrapes by HTTP status code.", |
| }, |
| []string{"code"}, |
| ) |
| // Initialize the most likely HTTP status codes. |
| cnt.WithLabelValues("200") |
| cnt.WithLabelValues("500") |
| cnt.WithLabelValues("503") |
| if err := reg.Register(cnt); err != nil { |
| if are, ok := err.(prometheus.AlreadyRegisteredError); ok { |
| cnt = are.ExistingCollector.(*prometheus.CounterVec) |
| } else { |
| panic(err) |
| } |
| } |
| |
| gge := prometheus.NewGauge(prometheus.GaugeOpts{ |
| Name: "promhttp_metric_handler_requests_in_flight", |
| Help: "Current number of scrapes being served.", |
| }) |
| if err := reg.Register(gge); err != nil { |
| if are, ok := err.(prometheus.AlreadyRegisteredError); ok { |
| gge = are.ExistingCollector.(prometheus.Gauge) |
| } else { |
| panic(err) |
| } |
| } |
| |
| return InstrumentHandlerCounter(cnt, InstrumentHandlerInFlight(gge, handler)) |
| } |
| |
| // HandlerErrorHandling defines how a Handler serving metrics will handle |
| // errors. |
| type HandlerErrorHandling int |
| |
| // These constants cause handlers serving metrics to behave as described if |
| // errors are encountered. |
| const ( |
| // Serve an HTTP status code 500 upon the first error |
| // encountered. Report the error message in the body. |
| HTTPErrorOnError HandlerErrorHandling = iota |
| // 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. 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 |
| ) |
| |
| // Logger is the minimal interface HandlerOpts needs for logging. Note that |
| // log.Logger from the standard library implements this interface, and it is |
| // easy to implement by custom loggers, if they don't do so already anyway. |
| type Logger interface { |
| Println(v ...interface{}) |
| } |
| |
| // HandlerOpts specifies options how to serve metrics via an http.Handler. The |
| // zero value of HandlerOpts is a reasonable default. |
| type HandlerOpts struct { |
| // ErrorLog specifies an optional logger for errors collecting and |
| // serving metrics. If nil, errors are not logged at all. |
| ErrorLog Logger |
| // ErrorHandling defines how errors are handled. Note that errors are |
| // 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 |
| // The number of concurrent HTTP requests is limited to |
| // MaxRequestsInFlight. Additional requests are responded to with 503 |
| // Service Unavailable and a suitable message in the body. If |
| // MaxRequestsInFlight is 0 or negative, no limit is applied. |
| MaxRequestsInFlight int |
| // If handling a request takes longer than Timeout, it is responded to |
| // with 503 ServiceUnavailable and a suitable Message. No timeout is |
| // applied if Timeout is 0 or negative. Note that with the current |
| // implementation, reaching the timeout simply ends the HTTP requests as |
| // described above (and even that only if sending of the body hasn't |
| // started yet), while the bulk work of gathering all the metrics keeps |
| // running in the background (with the eventual result to be thrown |
| // away). Until the implementation is improved, it is recommended to |
| // implement a separate timeout in potentially slow Collectors. |
| Timeout time.Duration |
| } |
| |
| // gzipAccepted returns whether the client will accept gzip-encoded content. |
| func gzipAccepted(header http.Header) bool { |
| a := header.Get(acceptEncodingHeader) |
| parts := strings.Split(a, ",") |
| for _, part := range parts { |
| part = strings.TrimSpace(part) |
| if part == "gzip" || strings.HasPrefix(part, "gzip;") { |
| return true |
| } |
| } |
| return false |
| } |
| |
| // httpError removes any content-encoding header and then calls http.Error with |
| // the provided error and http.StatusInternalServerErrer. Error contents is |
| // supposed to be uncompressed plain text. However, same as with a plain |
| // http.Error, any header settings will be void if the header has already been |
| // sent. The error message will still be written to the writer, but it will |
| // probably be of limited use. |
| func httpError(rsp http.ResponseWriter, err error) { |
| rsp.Header().Del(contentEncodingHeader) |
| http.Error( |
| rsp, |
| "An error has occurred while serving metrics:\n\n"+err.Error(), |
| http.StatusInternalServerError, |
| ) |
| } |