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Add a file lock to the data directory on startup to prevent multiple agents. #18483

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merged 3 commits into from
May 14, 2020
Merged

Add a file lock to the data directory on startup to prevent multiple agents. #18483

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e0c1359
Add a file lock to the data directory on startup to prevent multiple …
blakerouse May 13, 2020
2422e02
Add export comments to AppLocker.
blakerouse May 13, 2020
0744577
Fix periodic to not block startup.
blakerouse May 14, 2020
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50 changes: 50 additions & 0 deletions x-pack/elastic-agent/pkg/agent/application/locker.go
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Original file line number Diff line number Diff line change
@@ -0,0 +1,50 @@
// Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
// or more contributor license agreements. Licensed under the Elastic License;
// you may not use this file except in compliance with the Elastic License.

package application

import (
"fmt"
"os"
"path/filepath"

"github.com/gofrs/flock"
)

const lockFileName = "agent.lock"

// ErrAppAlreadyRunning error returned when another elastic-agent is already holding the lock.
var ErrAppAlreadyRunning = fmt.Errorf("another elastic-agent is already running")

// AppLocker locks the agent.lock file inside the provided directory.
type AppLocker struct {
lock *flock.Flock
}

// NewAppLocker creates an AppLocker that locks the agent.lock file inside the provided directory.
func NewAppLocker(dir string) *AppLocker {
if _, err := os.Stat(dir); os.IsNotExist(err) {
_ = os.Mkdir(dir, 0755)
}
return &AppLocker{
lock: flock.New(filepath.Join(dir, lockFileName)),
}
}

// TryLock tries to grab the lock file and returns error if it cannot.
func (a *AppLocker) TryLock() error {
locked, err := a.lock.TryLock()
if err != nil {
return err
}
if !locked {
return ErrAppAlreadyRunning
}
return nil
}

// Unlock releases the lock file.
func (a *AppLocker) Unlock() error {
return a.lock.Unlock()
}
29 changes: 29 additions & 0 deletions x-pack/elastic-agent/pkg/agent/application/locker_test.go
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Original file line number Diff line number Diff line change
@@ -0,0 +1,29 @@
// Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
// or more contributor license agreements. Licensed under the Elastic License;
// you may not use this file except in compliance with the Elastic License.

package application

import (
"io/ioutil"
"os"
"testing"

"github.com/stretchr/testify/assert"
"github.com/stretchr/testify/require"
)

func TestAppLocker(t *testing.T) {
tmp, _ := ioutil.TempDir("", "locker")
defer os.RemoveAll(tmp)

locker1 := NewAppLocker(tmp)
locker2 := NewAppLocker(tmp)

require.NoError(t, locker1.TryLock())
assert.Error(t, locker2.TryLock())
require.NoError(t, locker1.Unlock())
require.NoError(t, locker2.TryLock())
assert.Error(t, locker1.TryLock())
require.NoError(t, locker2.Unlock())
}
27 changes: 15 additions & 12 deletions x-pack/elastic-agent/pkg/agent/application/periodic.go
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Original file line number Diff line number Diff line change
Expand Up @@ -23,21 +23,24 @@ type periodic struct {
}

func (p *periodic) Start() error {
if err := p.work(); err != nil {
p.log.Debugf("Failed to read configuration, error: %s", err)
}

for {
select {
case <-p.done:
break
case <-time.After(p.period):
}

go func() {
if err := p.work(); err != nil {
p.log.Debugf("Failed to read configuration, error: %s", err)
}
}

for {
select {
case <-p.done:
break
case <-time.After(p.period):
}

if err := p.work(); err != nil {
p.log.Debugf("Failed to read configuration, error: %s", err)
}
}
}()
return nil
}

func (p *periodic) work() error {
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7 changes: 7 additions & 0 deletions x-pack/elastic-agent/pkg/agent/cmd/run.go
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,7 @@ import (
"github.com/spf13/cobra"

"github.com/elastic/beats/v7/x-pack/elastic-agent/pkg/agent/application"
"github.com/elastic/beats/v7/x-pack/elastic-agent/pkg/agent/application/paths"
"github.com/elastic/beats/v7/x-pack/elastic-agent/pkg/agent/errors"
"github.com/elastic/beats/v7/x-pack/elastic-agent/pkg/cli"
"github.com/elastic/beats/v7/x-pack/elastic-agent/pkg/config"
Expand Down Expand Up @@ -47,6 +48,12 @@ func run(flags *globalFlags, streams *cli.IOStreams) error {
return err
}

locker := application.NewAppLocker(paths.Data())
if err := locker.TryLock(); err != nil {
return err
}
defer locker.Unlock()
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can you make sure this is handled even if we are killed. defer statements are skipped if SIGINT or SIGTERM are received and it can prevent us from restarting

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I have verified that this does get called in all the cases defined below with signals.

signals := make(chan os.Signal, 1)
signal.Notify(signals, syscall.SIGINT, syscall.SIGKILL, syscall.SIGTERM, syscall.SIGQUIT)

<-signals

So the defer does get called. I did find a bug in periodic that was preventing app.Start from returning to catch the signals. I have fixed that in my most recent commit.


app, err := application.New(logger, pathConfigFile)
if err != nil {
return err
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2 changes: 1 addition & 1 deletion x-pack/elastic-agent/pkg/artifact/download/fs/downloader.go
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Expand Up @@ -42,7 +42,7 @@ func NewDownloader(config *artifact.Config) *Downloader {
func (e *Downloader) Download(_ context.Context, programName, version string) (string, error) {
// create a destination directory root/program
destinationDir := filepath.Join(e.config.TargetDirectory, programName)
if err := os.MkdirAll(destinationDir, os.ModeDir); err != nil {
if err := os.MkdirAll(destinationDir, 0755); err != nil {
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This is a drive-by fix on Mac os.ModeDir does not create the directory with the proper permissions. 0755 must be used.

return "", errors.New(err, "creating directory for downloaded artifact failed", errors.TypeFilesystem, errors.M(errors.MetaKeyPath, destinationDir))
}

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