metrics: Initial integration of Prometheus metrics (#3709)

Signed-off-by: Dave Henderson <dhenderson@gmail.com>

2 files changed, 164 insertions, 0 deletions

diff --git a/modules/metrics/adminmetrics.go b/modules/metrics/adminmetrics.go
new file mode 100644
index 0000000..f6a55e8
--- /dev/null
+++ b/modules/metrics/adminmetrics.go
@@ -0,0 +1,55 @@
+// Copyright 2020 Matthew Holt and The Caddy 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/caddyserver/caddy/v2"
+)
+
+func init() {
+	caddy.RegisterModule(AdminMetrics{})
+}
+
+// AdminMetrics is a module that serves a metrics endpoint so that any gathered
+// metrics can be exposed for scraping. This module is not configurable, and
+// is permanently mounted to the admin API endpoint at "/metrics".
+// See the Metrics module for a configurable endpoint that is usable if the
+// Admin API is disabled.
+type AdminMetrics struct{}
+
+// CaddyModule returns the Caddy module information.
+func (AdminMetrics) CaddyModule() caddy.ModuleInfo {
+	return caddy.ModuleInfo{
+		ID:  "admin.api.metrics",
+		New: func() caddy.Module { return new(AdminMetrics) },
+	}
+}
+
+// Routes returns a route for the /metrics endpoint.
+func (m *AdminMetrics) Routes() []caddy.AdminRoute {
+	metricsHandler := createMetricsHandler(nil)
+	h := caddy.AdminHandlerFunc(func(w http.ResponseWriter, r *http.Request) error {
+		metricsHandler.ServeHTTP(w, r)
+		return nil
+	})
+	return []caddy.AdminRoute{{Pattern: "/metrics", Handler: h}}
+}
+
+// Interface guards
+var (
+	_ caddy.AdminRouter = (*AdminMetrics)(nil)
+)
diff --git a/modules/metrics/metrics.go b/modules/metrics/metrics.go
new file mode 100644
index 0000000..eab6342
--- /dev/null
+++ b/modules/metrics/metrics.go
@@ -0,0 +1,109 @@
+// Copyright 2020 Matthew Holt and The Caddy 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/caddyserver/caddy/v2"
+	"github.com/caddyserver/caddy/v2/caddyconfig/caddyfile"
+	"github.com/caddyserver/caddy/v2/caddyconfig/httpcaddyfile"
+	"github.com/caddyserver/caddy/v2/modules/caddyhttp"
+
+	"go.uber.org/zap"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+)
+
+func init() {
+	caddy.RegisterModule(Metrics{})
+	httpcaddyfile.RegisterHandlerDirective("metrics", parseCaddyfile)
+}
+
+// Metrics is a module that serves a /metrics endpoint so that any gathered
+// metrics can be exposed for scraping. This module is configurable by end-users
+// unlike AdminMetrics.
+type Metrics struct {
+	metricsHandler http.Handler
+}
+
+// CaddyModule returns the Caddy module information.
+func (Metrics) CaddyModule() caddy.ModuleInfo {
+	return caddy.ModuleInfo{
+		ID:  "http.handlers.metrics",
+		New: func() caddy.Module { return new(Metrics) },
+	}
+}
+
+type zapLogger struct {
+	zl *zap.Logger
+}
+
+func (l *zapLogger) Println(v ...interface{}) {
+	l.zl.Sugar().Error(v...)
+}
+
+// Provision sets up m.
+func (m *Metrics) Provision(ctx caddy.Context) error {
+	log := ctx.Logger(m)
+	m.metricsHandler = createMetricsHandler(&zapLogger{log})
+	return nil
+}
+
+func parseCaddyfile(h httpcaddyfile.Helper) (caddyhttp.MiddlewareHandler, error) {
+	var m Metrics
+	err := m.UnmarshalCaddyfile(h.Dispenser)
+	return m, err
+}
+
+// UnmarshalCaddyfile sets up the handler from Caddyfile tokens. Syntax:
+//
+//     metrics <matcher>
+//
+func (m *Metrics) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
+	for d.Next() {
+		args := d.RemainingArgs()
+		if len(args) > 0 {
+			return d.ArgErr()
+		}
+	}
+	return nil
+}
+
+func (m Metrics) ServeHTTP(w http.ResponseWriter, r *http.Request, next caddyhttp.Handler) error {
+	m.metricsHandler.ServeHTTP(w, r)
+	return next.ServeHTTP(w, r)
+}
+
+// Interface guards
+var (
+	_ caddy.Provisioner           = (*Metrics)(nil)
+	_ caddyhttp.MiddlewareHandler = (*Metrics)(nil)
+	_ caddyfile.Unmarshaler       = (*Metrics)(nil)
+)
+
+func createMetricsHandler(logger promhttp.Logger) http.Handler {
+	return promhttp.InstrumentMetricHandler(prometheus.DefaultRegisterer,
+		promhttp.HandlerFor(prometheus.DefaultGatherer, promhttp.HandlerOpts{
+			// will only log errors if logger is non-nil
+			ErrorLog: logger,
+
+			// Allow OpenMetrics format to be negotiated - largely compatible,
+			// except quantile/le label values always have a decimal.
+			EnableOpenMetrics: true,
+		}),
+	)
+}