Add local Pyroscope server and Go continuous profiling

Add a docker-compose service running the Grafana Pyroscope backend on
port 4040 with a persistent data volume, and instrument the Go app via
github.com/grafana/pyroscope-go. The app pushes CPU, memory, and
goroutine profiles every 10s when pyroscope.enabled is set in
config.yaml. Config is extended with application_name and server_address
(defaults to http://localhost:4040). Document usage in the README.

1 files changed, 36 insertions, 0 deletions

diff --git a/main.go b/main.go
index 4404acf..8971433 100644
--- a/main.go
+++ b/main.go
@@ -3,7 +3,9 @@ package main
 import (
 	"database/sql"
 	"flag"
+	"log/slog"
 
+	"github.com/grafana/pyroscope-go"
 	"github.com/martinlehoux/biking_home/cli"
 	"github.com/martinlehoux/biking_home/config"
 	"github.com/martinlehoux/kagamigo/kcore"
@@ -18,8 +20,42 @@ func main() {
 	flag.Parse()
 	appConfig, err := config.Load(*configFile)
 	kcore.Expect(err, "failed to load configuration")
+	stopProfiler, err := startPyroscope(appConfig.Pyroscope)
+	if err != nil {
+		kcore.Expect(err, "failed to start pyroscope")
+	}
+	if stopProfiler != nil {
+		defer stopProfiler()
+	}
 	db, err := sql.Open("sqlite3", appConfig.Database.Path)
 	kcore.Expect(err, "failed to open database")
 	defer db.Close()
 	cli.Run(db, *configFile, appConfig)
 }
+
+// startPyroscope starts the continuous profiler when enabled in the config and
+// returns a stop function to flush and detach the profiler on shutdown, or nil
+// when pyroscope is disabled.
+func startPyroscope(appConfig config.PyroscopeConfig) (func(), error) {
+	if !appConfig.Enabled {
+		return nil, nil
+	}
+	profiler, err := pyroscope.Start(pyroscope.Config{
+		ApplicationName: appConfig.ApplicationName,
+		ServerAddress:   appConfig.ServerAddress,
+		Logger:          pyroscope.StandardLogger,
+		ProfileTypes: []pyroscope.ProfileType{
+			pyroscope.ProfileCPU,
+			pyroscope.ProfileAllocSpace,
+			pyroscope.ProfileAllocObjects,
+			pyroscope.ProfileInuseSpace,
+			pyroscope.ProfileInuseObjects,
+			pyroscope.ProfileGoroutines,
+		},
+	})
+	if err != nil {
+		return nil, err
+	}
+	slog.Info("pyroscope enabled", "server", appConfig.ServerAddress, "application", appConfig.ApplicationName)
+	return func() { _ = profiler.Stop() }, nil
+}