feat: add --pid-file option to write PID files (#25499)

Add `--pid-file` option to write PID files on startup. The PID filename
is specified by the argument after `--pid-file`. If the PID file already exists, influxd will exit unless the `--overwrite-pid-file` flag is also used.

Example: `influxd --pid-file /var/lib/influxd/influxd.pid`

PID files are automatically removed when the influxd process is shutdown.

Closes: #25498
(cherry picked from commit c35321b)
(cherry picked from commit 48f7600)

cmd/influxd/launcher/cmd.go

@@ -144,6 +144,9 @@ type InfluxdOpts struct {
 	TracingType       string
 	ReportingDisabled bool
 
+	PIDFile          string
+	OverwritePIDFile bool
+
 	AssetsPath string
 	BoltPath   string
 	SqLitePath string
@@ -213,6 +216,9 @@ func NewOpts(viper *viper.Viper) *InfluxdOpts {
 		FluxLogEnabled:    false,
 		ReportingDisabled: false,
 
+		PIDFile:          "",
+		OverwritePIDFile: false,
+
 		BoltPath:   filepath.Join(dir, bolt.DefaultFilename),
 		SqLitePath: filepath.Join(dir, sqlite.DefaultFilename),
 		EnginePath: filepath.Join(dir, "engine"),
@@ -325,6 +331,18 @@ 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.OverwritePIDFile,
+			Flag:    "overwrite-pid-file",
+			Default: o.OverwritePIDFile,
+			Desc:    "overwrite PID file if it already exists instead of exiting",
+		},
 		{
 			DestP:   &o.SessionLength,
 			Flag:    "session-length",

cmd/influxd/launcher/launcher.go

@@ -5,10 +5,12 @@ import (
 	"crypto/tls"
 	"errors"
 	"fmt"
+	"io/fs"
 	"net"
 	nethttp "net/http"
 	"os"
 	"path/filepath"
+	"strconv"
 	"strings"
 	"sync"
 	"time"
@@ -109,6 +111,11 @@ const (
 	JaegerTracing = "jaeger"
 )
 
+var (
+	// ErrPIDFileExists indicates that a PID file already exists.
+	ErrPIDFileExists = errors.New("PID file exists (possible unclean shutdown or another instance already running)")
+)
+
 type labeledCloser struct {
 	label  string
 	closer func(context.Context) error
@@ -248,6 +255,10 @@ func (m *Launcher) run(ctx context.Context, opts *InfluxdOpts) (err error) {
 		}
 	}
 
+	if err := m.writePIDFile(opts.PIDFile, opts.OverwritePIDFile); 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 +981,74 @@ func (m *Launcher) initTracing(opts *InfluxdOpts) {
 	}
 }
 
+// writePIDFile will write the process ID to pidFilename and register a cleanup function to delete it during
+// shutdown. If pidFilename is empty, then no PID file is written and no cleanup function is registered.
+// If pidFilename already exists and overwrite is false, then pidFilename is not overwritten and a
+// ErrPIDFileExists error is returned. If pidFilename already exists and overwrite is true, then pidFilename
+// will be overwritten but a warning will be logged.
+func (m *Launcher) writePIDFile(pidFilename string, overwrite bool) error {
+	if pidFilename == "" {
+		return nil
+	}
+
+	// Create directory to PIDfile if needed.
+	if err := os.MkdirAll(filepath.Dir(pidFilename), 0777); err != nil {
+		return fmt.Errorf("mkdir: %w", err)
+	}
+
+	// Write PID to file, but don't clobber an existing PID file.
+	pidBytes := []byte(strconv.Itoa(os.Getpid()))
+	pidMode := fs.FileMode(0666)
+	openFlags := os.O_WRONLY | os.O_CREATE | os.O_TRUNC
+	pidFile, err := os.OpenFile(pidFilename, openFlags|os.O_EXCL, pidMode)
+	if err != nil {
+		if !errors.Is(err, fs.ErrExist) {
+			return fmt.Errorf("open file: %w", err)
+		}
+		if !overwrite {
+			return ErrPIDFileExists
+		} else {
+			m.log.Warn("PID file already exists, attempting to overwrite", zap.String("pidFile", pidFilename))
+			pidFile, err = os.OpenFile(pidFilename, openFlags, pidMode)
+			if err != nil {
+				return fmt.Errorf("overwrite file: %w", err)
+			}
+		}
+	}
+	_, writeErr := pidFile.Write(pidBytes) // Contract says Write must return an error if count < len(pidBytes).
+	closeErr := pidFile.Close()            // always close the file
+	if writeErr != nil || closeErr != nil {
+		var errs []error
+		if writeErr != nil {
+			errs = append(errs, fmt.Errorf("write file: %w", writeErr))
+		}
+		if closeErr != nil {
+			errs = append(errs, fmt.Errorf("close file: %w", closeErr))
+		}
+
+		// Let's make sure we don't leave a PID file behind on error.
+		removeErr := os.Remove(pidFilename)
+		if removeErr != nil {
+			errs = append(errs, fmt.Errorf("remove file: %w", removeErr))
+		}
+
+		return errors.Join(errs...)
+	}
+
+	// Add a cleanup function.
+	m.closers = append(m.closers, labeledCloser{
+		label: "pidfile",
+		closer: func(context.Context) error {
+			if err := os.Remove(pidFilename); err != nil {
+				return fmt.Errorf("removing PID file %q: %w", pidFilename, 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_helpers.go

@@ -55,6 +55,8 @@ type TestLauncher struct {
 	Bucket *influxdb.Bucket
 	Auth   *influxdb.Authorization
 
+	Logger *zap.Logger
+
 	httpClient *httpc.Client
 	apiClient  *api.APIClient
 
@@ -146,7 +148,10 @@ func (tl *TestLauncher) Run(tb zaptest.TestingT, ctx context.Context, setters ..
 	}
 
 	// Set up top-level logger to write into the test-case.
-	tl.Launcher.log = zaptest.NewLogger(tb, zaptest.Level(opts.LogLevel)).With(zap.String("test_name", tb.Name()))
+	if tl.Logger == nil {
+		tl.Logger = zaptest.NewLogger(tb, zaptest.Level(opts.LogLevel)).With(zap.String("test_name", tb.Name()))
+	}
+	tl.Launcher.log = tl.Logger
 	return tl.Launcher.run(ctx, opts)
 }
 

cmd/influxd/launcher/launcher_test.go

@@ -3,8 +3,13 @@ package launcher_test
 import (
 	"context"
 	"encoding/json"
+	"fmt"
 	"io"
+	"io/fs"
 	nethttp "net/http"
+	"os"
+	"path/filepath"
+	"strconv"
 	"testing"
 	"time"
 
@@ -14,6 +19,10 @@ import (
 	"github.com/influxdata/influxdb/v2/http"
 	"github.com/influxdata/influxdb/v2/tenant"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"go.uber.org/zap"
+	"go.uber.org/zap/zapcore"
+	"go.uber.org/zap/zaptest/observer"
 )
 
 // Default context.
@@ -164,3 +173,129 @@ 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))
+}
+
+func TestLauncher_PIDFile_Locked(t *testing.T) {
+	pidDir := t.TempDir()
+	pidFilename := filepath.Join(pidDir, "influxd.pid")
+	lockContents := []byte("foobar") // something wouldn't appear in normal lock file
+
+	// Write PID file to lock out the launcher.
+	require.NoError(t, os.WriteFile(pidFilename, lockContents, 0666))
+	require.FileExists(t, pidFilename)
+	origSt, err := os.Stat(pidFilename)
+	require.NoError(t, err)
+
+	// Make sure we get an error about the PID file from the launcher
+	l := launcher.NewTestLauncher()
+	err = l.Run(t, ctx, func(o *launcher.InfluxdOpts) {
+		o.PIDFile = pidFilename
+	})
+	defer func() {
+		l.ShutdownOrFail(t, ctx)
+
+		require.FileExists(t, pidFilename)
+		contents, err := os.ReadFile(pidFilename)
+		require.NoError(t, err)
+		require.Equal(t, lockContents, contents)
+		curSt, err := os.Stat(pidFilename)
+		require.NoError(t, err)
+
+		// We can't compare origSt and curSt directly because even on mounts
+		// with "noatime" or "relatime" options, the sys.Atim field can still
+		// change. We'll just compare the most relevant exposed fields.
+		require.Equal(t, origSt.ModTime(), curSt.ModTime())
+		require.Equal(t, origSt.Mode(), curSt.Mode())
+	}()
+
+	require.ErrorIs(t, err, launcher.ErrPIDFileExists)
+	require.ErrorContains(t, err, fmt.Sprintf("error writing PIDFile %q: PID file exists (possible unclean shutdown or another instance already running)", pidFilename))
+}
+
+func TestLauncher_PIDFile_Overwrite(t *testing.T) {
+	pidDir := t.TempDir()
+	pidFilename := filepath.Join(pidDir, "influxd.pid")
+	lockContents := []byte("foobar") // something wouldn't appear in normal lock file
+
+	// Write PID file to lock out the launcher (or not in this case).
+	require.NoError(t, os.WriteFile(pidFilename, lockContents, 0666))
+	require.FileExists(t, pidFilename)
+
+	// Make sure we get an error about the PID file from the launcher.
+	l := launcher.NewTestLauncher()
+	loggerCore, ol := observer.New(zap.WarnLevel)
+	l.Logger = zap.New(loggerCore)
+	err := l.Run(t, ctx, func(o *launcher.InfluxdOpts) {
+		o.PIDFile = pidFilename
+		o.OverwritePIDFile = true
+	})
+	defer func() {
+		l.ShutdownOrFail(t, ctx)
+
+		require.NoFileExists(t, pidFilename)
+	}()
+	require.NoError(t, err)
+
+	expLogs := []observer.LoggedEntry{
+		{
+			Entry:   zapcore.Entry{Level: zap.WarnLevel, Message: "PID file already exists, attempting to overwrite"},
+			Context: []zapcore.Field{zap.String("pidFile", pidFilename)},
+		},
+	}
+	require.Equal(t, expLogs, ol.AllUntimed())
+	require.FileExists(t, pidFilename)
+	pidBytes, err := os.ReadFile(pidFilename)
+	require.NoError(t, err)
+	require.Equal(t, strconv.Itoa(os.Getpid()), string(pidBytes))
+}
+
+func TestLauncher_PIDFile_OverwriteFail(t *testing.T) {
+	if os.Geteuid() == 0 {
+		t.Skip("test will fail when run as root")
+	}
+
+	pidDir := t.TempDir()
+	pidFilename := filepath.Join(pidDir, "influxd.pid")
+	lockContents := []byte("foobar") // something wouldn't appear in normal lock file
+
+	// Write PID file to lock out the launcher.
+	require.NoError(t, os.WriteFile(pidFilename, lockContents, 0666))
+	require.FileExists(t, pidFilename)
+	require.NoError(t, os.Chmod(pidFilename, 0000))
+
+	// Make sure we get an error about the PID file from the launcher
+	l := launcher.NewTestLauncher()
+	err := l.Run(t, ctx, func(o *launcher.InfluxdOpts) {
+		o.PIDFile = pidFilename
+		o.OverwritePIDFile = true
+	})
+	defer func() {
+		l.ShutdownOrFail(t, ctx)
+
+		require.NoError(t, os.Chmod(pidFilename, 0644))
+		require.FileExists(t, pidFilename)
+		pidBytes, err := os.ReadFile(pidFilename)
+		require.NoError(t, err)
+		require.Equal(t, lockContents, pidBytes)
+	}()
+
+	require.ErrorContains(t, err, fmt.Sprintf("error writing PIDFile %[1]q: overwrite file: open %[1]s:", pidFilename))
+	require.ErrorIs(t, err, fs.ErrPermission)
+}