feat: add metrics system, move webhook feature to dedicated module (#372)

pkg/modules/prometheus/prometheus.go

@@ -0,0 +1,189 @@
+package prometheus
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"net/http"
+	"time"
+
+	"github.com/gotenberg/gotenberg/v7/pkg/gotenberg"
+	"github.com/gotenberg/gotenberg/v7/pkg/modules/api"
+	"github.com/labstack/echo/v4"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+	flag "github.com/spf13/pflag"
+)
+
+func init() {
+	gotenberg.MustRegisterModule(Prometheus{})
+}
+
+// Prometheus is a module which collects metrics and exposes them via an HTTP
+// route.
+type Prometheus struct {
+	namespace           string
+	interval            time.Duration
+	disableRouteLogging bool
+	disableCollect      bool
+
+	metrics  []gotenberg.Metric
+	registry *prometheus.Registry
+}
+
+// Descriptor returns a Prometheus's module descriptor.
+func (Prometheus) Descriptor() gotenberg.ModuleDescriptor {
+	return gotenberg.ModuleDescriptor{
+		ID: "prometheus",
+		FlagSet: func() *flag.FlagSet {
+			fs := flag.NewFlagSet("prometheus", flag.ExitOnError)
+			fs.String("prometheus-namespace", "gotenberg", "Set the namespace of modules' metrics")
+			fs.Duration("prometheus-collect-interval", time.Duration(1)*time.Second, "Set the interval for collecting modules' metrics")
+			fs.Bool("prometheus-disable-route-logging", false, "Disable the route logging")
+			fs.Bool("prometheus-disable-collect", false, "Disable the collect of metrics")
+
+			return fs
+		}(),
+		New: func() gotenberg.Module { return new(Prometheus) },
+	}
+}
+
+// Provision sets the modules properties.
+func (mod *Prometheus) Provision(ctx *gotenberg.Context) error {
+	flags := ctx.ParsedFlags()
+	mod.namespace = flags.MustString("prometheus-namespace")
+	mod.interval = flags.MustDuration("prometheus-collect-interval")
+	mod.disableRouteLogging = flags.MustBool("prometheus-disable-route-logging")
+	mod.disableCollect = flags.MustBool("prometheus-disable-collect")
+
+	if mod.disableCollect {
+		// Exit early.
+		return nil
+	}
+
+	// Get metrics from modules.
+	mods, err := ctx.Modules(new(gotenberg.MetricsProvider))
+	if err != nil {
+		return fmt.Errorf("get metrics providers: %w", err)
+	}
+
+	metricsProviders := make([]gotenberg.MetricsProvider, len(mods))
+	for i, metricsProvider := range mods {
+		metricsProviders[i] = metricsProvider.(gotenberg.MetricsProvider)
+	}
+
+	for _, metricsProvider := range metricsProviders {
+		metrics, err := metricsProvider.Metrics()
+		if err != nil {
+			return fmt.Errorf("get metrics: %w", err)
+		}
+
+		mod.metrics = append(mod.metrics, metrics...)
+	}
+
+	mod.registry = prometheus.NewRegistry()
+
+	return nil
+}
+
+// Validate validates the module properties.
+func (mod Prometheus) Validate() error {
+	if mod.disableCollect {
+		// Exit early.
+		return nil
+	}
+
+	if mod.namespace == "" {
+		return errors.New("namespace must not be empty")
+	}
+
+	metricsMap := make(map[string]string, len(mod.metrics))
+
+	for _, metric := range mod.metrics {
+		if metric.Name == "" {
+			return errors.New("metric name cannot be empty")
+		}
+
+		if metric.Read == nil {
+			return fmt.Errorf("metric '%s' has nil read method", metric.Name)
+		}
+
+		if _, ok := metricsMap[metric.Name]; ok {
+			return fmt.Errorf("metric '%s' is already registered", metric.Name)
+		}
+
+		metricsMap[metric.Name] = metric.Name
+	}
+
+	return nil
+}
+
+// Start starts the collect.
+func (mod Prometheus) Start() error {
+	if mod.disableCollect {
+		// Exit early.
+		return nil
+	}
+
+	for _, metric := range mod.metrics {
+		gauge := prometheus.NewGauge(
+			prometheus.GaugeOpts{
+				Namespace: mod.namespace,
+				Name:      metric.Name,
+				Help:      metric.Description,
+			},
+		)
+
+		mod.registry.MustRegister(gauge)
+
+		go func(gauge prometheus.Gauge, metric gotenberg.Metric) {
+			for {
+				gauge.Set(metric.Read())
+				time.Sleep(mod.interval)
+			}
+		}(gauge, metric)
+	}
+
+	return nil
+}
+
+// StartupMessage returns a custom startup message.
+func (mod Prometheus) StartupMessage() string {
+	if mod.disableCollect {
+		return "application not started (collect disabled by user)"
+	}
+
+	return "collecting metrics"
+}
+
+// Stop does nothing.
+func (mod Prometheus) Stop(_ context.Context) error {
+	return nil
+}
+
+// Routes returns the HTTP route.
+func (mod Prometheus) Routes() ([]api.Route, error) {
+	if mod.disableCollect {
+		return nil, nil
+	}
+
+	return []api.Route{
+		{
+			Method:         http.MethodGet,
+			Path:           "/prometheus/metrics",
+			DisableLogging: mod.disableRouteLogging,
+			Handler: echo.WrapHandler(
+				promhttp.HandlerFor(mod.registry, promhttp.HandlerOpts{}),
+			),
+		},
+	}, nil
+}
+
+// Interface guards.
+var (
+	_ gotenberg.Module      = (*Prometheus)(nil)
+	_ gotenberg.Provisioner = (*Prometheus)(nil)
+	_ gotenberg.Validator   = (*Prometheus)(nil)
+	_ gotenberg.App         = (*Prometheus)(nil)
+	_ api.Router            = (*Prometheus)(nil)
+)