Merge pull request #83722 from RainbowMango/pr_introduce_promhttp

Introduce http handler to metrics stability framework

staging/src/k8s.io/component-base/metrics/BUILD

@@ -6,6 +6,7 @@ go_library(
         "counter.go",
         "gauge.go",
         "histogram.go",
+        "http.go",
         "labels.go",
         "metric.go",
         "opts.go",
@@ -24,6 +25,7 @@ go_library(
         "//staging/src/k8s.io/component-base/version:go_default_library",
         "//vendor/github.com/blang/semver:go_default_library",
         "//vendor/github.com/prometheus/client_golang/prometheus:go_default_library",
+        "//vendor/github.com/prometheus/client_golang/prometheus/promhttp:go_default_library",
         "//vendor/github.com/prometheus/client_model/go:go_default_library",
         "//vendor/github.com/prometheus/procfs:go_default_library",
         "//vendor/k8s.io/klog:go_default_library",

staging/src/k8s.io/component-base/metrics/http.go

@@ -0,0 +1,63 @@
+/*
+Copyright 2019 The Kubernetes 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 metrics
+
+import (
+	"net/http"
+
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+)
+
+// 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 promhttp.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
+)
+
+// HandlerOpts specifies options how to serve metrics via an http.Handler. The
+// zero value of HandlerOpts is a reasonable default.
+type HandlerOpts promhttp.HandlerOpts
+
+func (ho *HandlerOpts) toPromhttpHandlerOpts() promhttp.HandlerOpts {
+	return promhttp.HandlerOpts(*ho)
+}
+
+// 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 Gatherer, opts HandlerOpts) http.Handler {
+	return promhttp.HandlerFor(reg, opts.toPromhttpHandlerOpts())
+}