feat: add --pid-file option to write PID files

cmd/influxd/launcher/cmd.go

@@ -144,6 +144,8 @@ type InfluxdOpts struct {
 	TracingType       string
 	ReportingDisabled bool
 
+	PIDFile string
+
 	AssetsPath string
 	BoltPath   string
 	SqLitePath string
@@ -213,6 +215,8 @@ func NewOpts(viper *viper.Viper) *InfluxdOpts {
 		FluxLogEnabled:    false,
 		ReportingDisabled: false,
 
+		PIDFile: "",
+
 		BoltPath:   filepath.Join(dir, bolt.DefaultFilename),
 		SqLitePath: filepath.Join(dir, sqlite.DefaultFilename),
 		EnginePath: filepath.Join(dir, "engine"),
@@ -325,6 +329,12 @@ func (o *InfluxdOpts) BindCliOpts() []cli.Opt {
 			Default: o.ReportingDisabled,
 			Desc:    "disable sending telemetry data to https://telemetry.influxdata.com every 8 hours",
 		},
+		{
+			DestP:   &o.PIDFile,
+			Flag:    "pid-file",
+			Default: o.PIDFile,
+			Desc:    "write process ID to a file",
+		},
 		{
 			DestP:   &o.SessionLength,
 			Flag:    "session-length",

cmd/influxd/launcher/launcher.go

@@ -9,6 +9,7 @@ import (
 	nethttp "net/http"
 	"os"
 	"path/filepath"
+	"strconv"
 	"strings"
 	"sync"
 	"time"
@@ -248,6 +249,10 @@ func (m *Launcher) run(ctx context.Context, opts *InfluxdOpts) (err error) {
 		}
 	}
 
+	if err := m.writePIDFile(opts.PIDFile); err != nil {
+		return fmt.Errorf("error writing PIDFile %q: %w", opts.PIDFile, err)
+	}
+
 	m.reg = prom.NewRegistry(m.log.With(zap.String("service", "prom_registry")))
 	m.reg.MustRegister(collectors.NewGoCollector())
 
@@ -970,6 +975,40 @@ func (m *Launcher) initTracing(opts *InfluxdOpts) {
 	}
 }
 
+// writePIDFile will write the process ID to pidFile and register a cleanup function to delete it during
+// shutdown. If pidFile is empty, then no PID file is written and no cleanup function is registered.
+func (m *Launcher) writePIDFile(pidFile string) error {
+	if pidFile == "" {
+		return nil
+	}
+
+	// Create directory to PIDfile if needed.
+	if err := os.MkdirAll(filepath.Dir(pidFile), 0777); err != nil {
+		return fmt.Errorf("mkdir: %w", err)
+	}
+
+	// Write PID to file
+	pidStr := strconv.Itoa(os.Getpid())
+	if writeErr := os.WriteFile(pidFile, []byte(pidStr), 0666); writeErr != nil {
+		// Let's make sure we don't leave a PID file behind on error.
+		removeErr := os.Remove(pidFile)
+		return fmt.Errorf("write file: %w; remove file: %w", writeErr, removeErr)
+	}
+
+	// Add a cleanup function.
+	m.closers = append(m.closers, labeledCloser{
+		label: "pidfile",
+		closer: func(context.Context) error {
+			if err := os.Remove(pidFile); err != nil {
+				return fmt.Errorf("removing PID file %q: %w", pidFile, err)
+			}
+			return nil
+		},
+	})
+
+	return nil
+}
+
 // openMetaStores opens the embedded DBs used to store metadata about influxd resources, migrating them to
 // the latest schema expected by the server.
 // On success, a unique ID is returned to be used as an identifier for the influxd instance in telemetry.

cmd/influxd/launcher/launcher_test.go

@@ -5,6 +5,9 @@ import (
 	"encoding/json"
 	"io"
 	nethttp "net/http"
+	"os"
+	"path/filepath"
+	"strconv"
 	"testing"
 	"time"
 
@@ -14,6 +17,7 @@ import (
 	"github.com/influxdata/influxdb/v2/http"
 	"github.com/influxdata/influxdb/v2/tenant"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 // Default context.
@@ -164,3 +168,21 @@ func TestLauncher_PingHeaders(t *testing.T) {
 	assert.Equal(t, []string{"OSS"}, resp.Header.Values("X-Influxdb-Build"))
 	assert.Equal(t, []string{"dev"}, resp.Header.Values("X-Influxdb-Version"))
 }
+
+func TestLauncher_PIDFile(t *testing.T) {
+	pidDir := t.TempDir()
+	pidFilename := filepath.Join(pidDir, "influxd.pid")
+
+	l := launcher.RunAndSetupNewLauncherOrFail(ctx, t, func(o *launcher.InfluxdOpts) {
+		o.PIDFile = pidFilename
+	})
+	defer func() {
+		l.ShutdownOrFail(t, ctx)
+		require.NoFileExists(t, pidFilename)
+	}()
+
+	require.FileExists(t, pidFilename)
+	pidBytes, err := os.ReadFile(pidFilename)
+	require.NoError(t, err)
+	require.Equal(t, strconv.Itoa(os.Getpid()), string(pidBytes))
+}