[feature] Initial Prometheus metrics implementation (#2334)

* feat: Initial OTEL metrics

* docs: add metrics documentation

* fix: metrics endpoint conditional check

* feat: metrics endpoint basic auth

* fix: make metrics-auth-enabled default false

* fix: go fmt helpers.gen.go

* fix: add metric-related env vars to envparsing.sh

* fix: metrics docs

* fix: metrics related stuff in envparsing.sh

* fix: metrics docs

* chore: metrics docs wording

* fix: metrics stuff in envparsing?

* bump otel versions

---------

Co-authored-by: Tsuribori <user@acertaindebian>
Co-authored-by: Tsuribori <none@example.org>
Co-authored-by: tsmethurst <tobi.smethurst@protonmail.com>

8 files changed, 283 insertions, 0 deletions

diff --git a/internal/config/config.go b/internal/config/config.go
index b7d2eff36..173999b53 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -140,6 +140,11 @@ type Configuration struct {
 	TracingEndpoint          string `name:"tracing-endpoint" usage:"Endpoint of your trace collector. Eg., 'localhost:4317' for gRPC, 'localhost:4318' for http"`
 	TracingInsecureTransport bool   `name:"tracing-insecure-transport" usage:"Disable TLS for the gRPC or HTTP transport protocol"`
 
+	MetricsEnabled      bool   `name:"metrics-enabled" usage:"Enable OpenTelemetry based metrics support."`
+	MetricsAuthEnabled  bool   `name:"metrics-auth-enabled" usage:"Enable HTTP Basic Authentication for Prometheus metrics endpoint"`
+	MetricsAuthUsername string `name:"metrics-auth-username" usage:"Username for Prometheus metrics endpoint"`
+	MetricsAuthPassword string `name:"metrics-auth-password" usage:"Password for Prometheus metrics endpoint"`
+
 	SMTPHost               string `name:"smtp-host" usage:"Host of the smtp server. Eg., 'smtp.eu.mailgun.org'"`
 	SMTPPort               int    `name:"smtp-port" usage:"Port of the smtp server. Eg., 587"`
 	SMTPUsername           string `name:"smtp-username" usage:"Username to authenticate with the smtp server as. Eg., 'postmaster@mail.example.org'"`
diff --git a/internal/config/defaults.go b/internal/config/defaults.go
index 3da489501..5aba6c689 100644
--- a/internal/config/defaults.go
+++ b/internal/config/defaults.go
@@ -121,6 +121,9 @@ var Defaults = Configuration{
 	TracingEndpoint:          "",
 	TracingInsecureTransport: false,
 
+	MetricsEnabled:     false,
+	MetricsAuthEnabled: false,
+
 	SyslogEnabled:  false,
 	SyslogProtocol: "udp",
 	SyslogAddress:  "localhost:514",
diff --git a/internal/config/helpers.gen.go b/internal/config/helpers.gen.go
index a008092d3..393a1b1e9 100644
--- a/internal/config/helpers.gen.go
+++ b/internal/config/helpers.gen.go
@@ -2100,6 +2100,106 @@ func GetTracingInsecureTransport() bool { return global.GetTracingInsecureTransp
 // SetTracingInsecureTransport safely sets the value for global configuration 'TracingInsecureTransport' field
 func SetTracingInsecureTransport(v bool) { global.SetTracingInsecureTransport(v) }
 
+// GetMetricsEnabled safely fetches the Configuration value for state's 'MetricsEnabled' field
+func (st *ConfigState) GetMetricsEnabled() (v bool) {
+	st.mutex.RLock()
+	v = st.config.MetricsEnabled
+	st.mutex.RUnlock()
+	return
+}
+
+// SetMetricsEnabled safely sets the Configuration value for state's 'MetricsEnabled' field
+func (st *ConfigState) SetMetricsEnabled(v bool) {
+	st.mutex.Lock()
+	defer st.mutex.Unlock()
+	st.config.MetricsEnabled = v
+	st.reloadToViper()
+}
+
+// MetricsEnabledFlag returns the flag name for the 'MetricsEnabled' field
+func MetricsEnabledFlag() string { return "metrics-enabled" }
+
+// GetMetricsEnabled safely fetches the value for global configuration 'MetricsEnabled' field
+func GetMetricsEnabled() bool { return global.GetMetricsEnabled() }
+
+// SetMetricsEnabled safely sets the value for global configuration 'MetricsEnabled' field
+func SetMetricsEnabled(v bool) { global.SetMetricsEnabled(v) }
+
+// GetMetricsAuthEnabled safely fetches the Configuration value for state's 'MetricsAuthEnabled' field
+func (st *ConfigState) GetMetricsAuthEnabled() (v bool) {
+	st.mutex.RLock()
+	v = st.config.MetricsAuthEnabled
+	st.mutex.RUnlock()
+	return
+}
+
+// SetMetricsAuthEnabled safely sets the Configuration value for state's 'MetricsAuthEnabled' field
+func (st *ConfigState) SetMetricsAuthEnabled(v bool) {
+	st.mutex.Lock()
+	defer st.mutex.Unlock()
+	st.config.MetricsAuthEnabled = v
+	st.reloadToViper()
+}
+
+// MetricsAuthEnabledFlag returns the flag name for the 'MetricsAuthEnabled' field
+func MetricsAuthEnabledFlag() string { return "metrics-auth-enabled" }
+
+// GetMetricsAuthEnabled safely fetches the value for global configuration 'MetricsAuthEnabled' field
+func GetMetricsAuthEnabled() bool { return global.GetMetricsAuthEnabled() }
+
+// SetMetricsAuthEnabled safely sets the value for global configuration 'MetricsAuthEnabled' field
+func SetMetricsAuthEnabled(v bool) { global.SetMetricsAuthEnabled(v) }
+
+// GetMetricsAuthUsername safely fetches the Configuration value for state's 'MetricsAuthUsername' field
+func (st *ConfigState) GetMetricsAuthUsername() (v string) {
+	st.mutex.RLock()
+	v = st.config.MetricsAuthUsername
+	st.mutex.RUnlock()
+	return
+}
+
+// SetMetricsAuthUsername safely sets the Configuration value for state's 'MetricsAuthUsername' field
+func (st *ConfigState) SetMetricsAuthUsername(v string) {
+	st.mutex.Lock()
+	defer st.mutex.Unlock()
+	st.config.MetricsAuthUsername = v
+	st.reloadToViper()
+}
+
+// MetricsAuthUsernameFlag returns the flag name for the 'MetricsAuthUsername' field
+func MetricsAuthUsernameFlag() string { return "metrics-auth-username" }
+
+// GetMetricsAuthUsername safely fetches the value for global configuration 'MetricsAuthUsername' field
+func GetMetricsAuthUsername() string { return global.GetMetricsAuthUsername() }
+
+// SetMetricsAuthUsername safely sets the value for global configuration 'MetricsAuthUsername' field
+func SetMetricsAuthUsername(v string) { global.SetMetricsAuthUsername(v) }
+
+// GetMetricsAuthPassword safely fetches the Configuration value for state's 'MetricsAuthPassword' field
+func (st *ConfigState) GetMetricsAuthPassword() (v string) {
+	st.mutex.RLock()
+	v = st.config.MetricsAuthPassword
+	st.mutex.RUnlock()
+	return
+}
+
+// SetMetricsAuthPassword safely sets the Configuration value for state's 'MetricsAuthPassword' field
+func (st *ConfigState) SetMetricsAuthPassword(v string) {
+	st.mutex.Lock()
+	defer st.mutex.Unlock()
+	st.config.MetricsAuthPassword = v
+	st.reloadToViper()
+}
+
+// MetricsAuthPasswordFlag returns the flag name for the 'MetricsAuthPassword' field
+func MetricsAuthPasswordFlag() string { return "metrics-auth-password" }
+
+// GetMetricsAuthPassword safely fetches the value for global configuration 'MetricsAuthPassword' field
+func GetMetricsAuthPassword() string { return global.GetMetricsAuthPassword() }
+
+// SetMetricsAuthPassword safely sets the value for global configuration 'MetricsAuthPassword' field
+func SetMetricsAuthPassword(v string) { global.SetMetricsAuthPassword(v) }
+
 // GetSMTPHost safely fetches the Configuration value for state's 'SMTPHost' field
 func (st *ConfigState) GetSMTPHost() (v string) {
 	st.mutex.RLock()
diff --git a/internal/db/bundb/bundb.go b/internal/db/bundb/bundb.go
index a86a20274..2559b8d58 100644
--- a/internal/db/bundb/bundb.go
+++ b/internal/db/bundb/bundb.go
@@ -40,6 +40,7 @@ import (
 	"github.com/superseriousbusiness/gotosocial/internal/db/bundb/migrations"
 	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
 	"github.com/superseriousbusiness/gotosocial/internal/log"
+	"github.com/superseriousbusiness/gotosocial/internal/metrics"
 	"github.com/superseriousbusiness/gotosocial/internal/state"
 	"github.com/superseriousbusiness/gotosocial/internal/tracing"
 	"github.com/uptrace/bun"
@@ -142,6 +143,9 @@ func NewBunDBService(ctx context.Context, state *state.State) (db.DB, error) {
 	if config.GetTracingEnabled() {
 		db.AddQueryHook(tracing.InstrumentBun())
 	}
+	if config.GetMetricsEnabled() {
+		db.AddQueryHook(metrics.InstrumentBun())
+	}
 
 	// table registration is needed for many-to-many, see:
 	// https://bun.uptrace.dev/orm/many-to-many-relation/
diff --git a/internal/metrics/metrics.go b/internal/metrics/metrics.go
new file mode 100644
index 000000000..966f346fd
--- /dev/null
+++ b/internal/metrics/metrics.go
@@ -0,0 +1,82 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+//go:build !nometrics
+
+package metrics
+
+import (
+	"errors"
+
+	"github.com/gin-gonic/gin"
+	"github.com/superseriousbusiness/gotosocial/internal/config"
+	"github.com/technologize/otel-go-contrib/otelginmetrics"
+	"github.com/uptrace/bun"
+	"github.com/uptrace/bun/extra/bunotel"
+	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/exporters/prometheus"
+	sdk "go.opentelemetry.io/otel/sdk/metric"
+	"go.opentelemetry.io/otel/sdk/resource"
+	semconv "go.opentelemetry.io/otel/semconv/v1.17.0"
+)
+
+const (
+	serviceName = "GoToSocial"
+)
+
+func Initialize() error {
+	if !config.GetMetricsEnabled() {
+		return nil
+	}
+
+	if config.GetMetricsAuthEnabled() {
+		if config.GetMetricsAuthPassword() == "" || config.GetMetricsAuthUsername() == "" {
+			return errors.New("metrics-auth-username and metrics-auth-password must be set when metrics-auth-enabled is true")
+		}
+	}
+
+	r, _ := resource.Merge(
+		resource.Default(),
+		resource.NewWithAttributes(
+			semconv.SchemaURL,
+			semconv.ServiceName(serviceName),
+		),
+	)
+
+	prometheusExporter, err := prometheus.New()
+	if err != nil {
+		return err
+	}
+
+	meterProvider := sdk.NewMeterProvider(
+		sdk.WithResource(r),
+		sdk.WithReader(prometheusExporter),
+	)
+	otel.SetMeterProvider(meterProvider)
+
+	return nil
+}
+
+func InstrumentGin() gin.HandlerFunc {
+	return otelginmetrics.Middleware(serviceName)
+}
+
+func InstrumentBun() bun.QueryHook {
+	return bunotel.NewQueryHook(
+		bunotel.WithMeterProvider(otel.GetMeterProvider()),
+	)
+}
diff --git a/internal/metrics/no_metrics.go b/internal/metrics/no_metrics.go
new file mode 100644
index 000000000..590a3fbf8
--- /dev/null
+++ b/internal/metrics/no_metrics.go
@@ -0,0 +1,43 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+//go:build nometrics
+
+package metrics
+
+import (
+	"errors"
+
+	"github.com/gin-gonic/gin"
+	"github.com/superseriousbusiness/gotosocial/internal/config"
+	"github.com/uptrace/bun"
+)
+
+func Initialize() error {
+	if config.GetMetricsEnabled() {
+		return errors.New("metrics was disabled at build time")
+	}
+	return nil
+}
+
+func InstrumentGin() gin.HandlerFunc {
+	return func(c *gin.Context) {}
+}
+
+func InstrumentBun() bun.QueryHook {
+	return nil
+}
diff --git a/internal/web/metrics.go b/internal/web/metrics.go
new file mode 100644
index 000000000..eb5530290
--- /dev/null
+++ b/internal/web/metrics.go
@@ -0,0 +1,33 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package web
+
+import (
+	"github.com/gin-gonic/gin"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+)
+
+const (
+	metricsPath = "/metrics"
+	metricsUser = "metrics"
+)
+
+func (m *Module) metricsGETHandler(c *gin.Context) {
+	h := promhttp.Handler()
+	h.ServeHTTP(c.Writer, c.Request)
+}
diff --git a/internal/web/web.go b/internal/web/web.go
index 86e74d6f8..6a21a754b 100644
--- a/internal/web/web.go
+++ b/internal/web/web.go
@@ -110,6 +110,19 @@ func (m *Module) Route(r *router.Router, mi ...gin.HandlerFunc) {
 	r.AttachHandler(http.MethodGet, domainBlockListPath, m.domainBlockListGETHandler)
 	r.AttachHandler(http.MethodGet, tagsPath, m.tagGETHandler)
 
+	// Prometheus metrics export endpoint
+	if config.GetMetricsEnabled() {
+		metricsGroup := r.AttachGroup(metricsPath)
+		metricsGroup.Use(mi...)
+		// Attach basic auth if enabled
+		if config.GetMetricsAuthEnabled() {
+			metricsGroup.Use(gin.BasicAuth(gin.Accounts{
+				config.GetMetricsAuthUsername(): config.GetMetricsAuthPassword(),
+			}))
+		}
+		metricsGroup.Handle(http.MethodGet, "", m.metricsGETHandler)
+	}
+
 	// Attach redirects from old endpoints to current ones for backwards compatibility
 	r.AttachHandler(http.MethodGet, "/auth/edit", func(c *gin.Context) { c.Redirect(http.StatusMovedPermanently, userPanelPath) })
 	r.AttachHandler(http.MethodGet, "/user", func(c *gin.Context) { c.Redirect(http.StatusMovedPermanently, userPanelPath) })