chanbackup: archive old channel backup files #9232

Abdulkbk · 2024-10-29T11:14:01Z

Change Description

To ensure that certain classes of recovery are always possible, we should considering adding a mode to never delete channel backups, and only rename or move them to a special folder that stores archived channels. They're relatively small (~300 bytes or so), so it shouldn't take up a significant amount of disk space.

This PR allows for the archiving of channel backups, enabling users to choose whether to permanently delete previous backup files or archive them by moving them to a designated archives folder.

Problem:
LND currently overwrites old channel backup files when creating new ones. This means:

If a user accidentally deletes a channel backup file, the backup is irretrievably lost.
If a newly created backup file becomes corrupted and no older backups are preserved, recovering the channel through the file becomes impossible.
In certain cases, users may want to compare older and newer backups to verify that the evolution of the channel states was valid.

Solution:
We modify the current flow of creating channel.backup. We start by creating a folder in the same directory where we store the channel.backup file (chan-backup-archives). We ensure that the channel.backup file is copied to the archive directory and timestamped before finally replacing it with the new file.

We set the LND's default behavior to archive old channel backups, but we provide a configuration option that can be passed as an argument or specified in lnd.conf to disable this behavior. This option allows LND to delete channel.backup files instead of archiving them. This can be achieved by setting disable-backup-archive=true in lnd.conf or passed as argument:

lnd --disable-backup-archive

Steps to Test

Start LND (make sure disable-backup-archive=true is not set in lnd.conf):

lnd

Trigger the channel backup process. This can be achieved by generating some blocks. If you're using BTCD backend:

btcctl generate 6

Stop LND and check the directory where the channel.backup file is stored. You will find a new folder called chan-backup-archives, where the backup files are archived.

To test disabling this feature

Start LND

lnd # if disable-backup-archive=true is set in lnd.conf

# or

lnd --disable-backup-archive # pass as arg

Repeat 2 & 3. This time the chan-backup-archives directory will not be created (if it does not already exist). If it already exists a new archive will not be created.

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Tests covering the positive and negative (error paths) are included.
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There is a change description in the release notes, or [skip ci] in the commit message for small changes.

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coderabbitai · 2024-10-29T11:14:09Z

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chanbackup/backupfile_test.go

lightninglabs-deploy · 2025-01-06T00:24:56Z

@Abdulkbk, remember to re-request review from reviewers when ready

MPins · 2025-01-06T20:09:46Z

LGTM 👌

chanbackup/backupfile_test.go

yyforyongyu · 2025-01-07T03:16:29Z

Could you do a rebase and push so the CI can run again, wanna check what's going in the logs but they are expired.

Abdulkbk · 2025-01-07T07:07:42Z

I've rebased and pushed
@yyforyongyu

yyforyongyu · 2025-01-08T06:12:25Z

chanbackup/backupfile.go

@@ -147,3 +173,48 @@ func (b *MultiFile) ExtractMulti(keyChain keychain.KeyRing) (*Multi, error) {
 	packedMulti := PackedMulti(multiBytes)
 	return packedMulti.Unpack(keyChain)
 }
+
+func createArchiveFile(archiveDir string, fileName string) error {


nit: missing godocs

wow, nice catch 👍

yyforyongyu · 2025-01-08T06:25:07Z

chanbackup/backupfile.go

+	}
+
+	return nil
+}


think ade9d50 should be squashed into this commit instead since it's testing the newly introduced method createArchiveFile.

Makes sense

yyforyongyu · 2025-01-08T06:25:57Z

chanbackup/backupfile.go

@@ -17,6 +19,10 @@ const (
 	// file that we'll use to atomically update the primary back up file
 	// when new channel are detected.
 	DefaultTempBackupFileName = "temp-dont-use.backup"
+
+	// DefaultChanBackupDirName is the default name of the directory that


Suggested change

// DefaultChanBackupDirName is the default name of the directory that

// DefaultChanBackupArchiveDirName is the default name of the directory that

yyforyongyu · 2025-01-08T06:26:51Z

chanbackup/backupfile_test.go

+
+	// First, we'll create a temporary directory for our test files.
+	tempDir := t.TempDir()
+	archiveDir := filepath.Join(tempDir, "chan-backup-archives")


use the var DefaultChanBackupArchiveDirName?

yyforyongyu · 2025-01-08T06:27:18Z

chanbackup/backupfile_test.go

+	archiveDir := filepath.Join(tempDir, "chan-backup-archives")
+
+	// Next, we'll create a test backup file and write some content to it.
+	backupFile := filepath.Join(tempDir, "channel.backup")


use the var DefaultBackupFileName

yyforyongyu · 2025-01-08T07:08:54Z

chanbackup/backupfile.go

@@ -117,6 +130,19 @@ func (b *MultiFile) UpdateAndSwap(newBackup PackedMulti) error {
 		return fmt.Errorf("unable to close file: %w", err)
 	}

+	// We check if the main backup file exists, if it does we archive it
+	// before replacing it with the new backup.
+	if _, err := os.Stat(b.fileName); err == nil {


Q: should we return the error here instead?

If we return an error here, LND will fail to start during the first run because channel.backup does not exist then. Should we add a log here instead?

I will also update the comment to capture this.

yyforyongyu · 2025-01-08T07:13:09Z

config.go

@@ -360,6 +366,8 @@ type Config struct {
 	MaxPendingChannels int    `long:"maxpendingchannels" description:"The maximum number of incoming pending channels permitted per peer."`
 	BackupFilePath     string `long:"backupfilepath" description:"The target location of the channel backup file"`

+	DisableBackupArchive bool `long:"disable-backup-archive" description:"If set to true, channel backups will be deleted or replaced rather than being archived to a separate location."`


think it'd be better if we could name it ArchiveBackup - then we don't need to use a double negative to decide whether we wanna create this archive or not.

The problem with this approach is when you try to disable this feature (since its enabled by default) using a CLI arg. Running the command lnd --archivebackup=false results in an error although setting archivebackup=false in the lnd.conf file works fine.

I think the alternative is to disable this feature by default and then the user can then run lnd --archivebackup to enable it without getting any errors. In this case there won't be any need for lnd --archivebackup=false

yyforyongyu · 2025-01-08T07:13:41Z

docs/release-notes/release-notes-0.19.0.md

@@ -74,6 +74,9 @@
  This is a protocol gadget required for Dynamic Commitments and Splicing that
  will be added later.

+* Add support for [archiving channel backup](https://github.com/lightningnetwork/lnd/pull/9232)
+ in a designated folder which allows for easy referencing in the future.


should also mention the newly introduced config value here.

yyforyongyu · 2025-01-08T07:25:13Z

chanbackup/backupfile.go

@@ -117,6 +134,21 @@ func (b *MultiFile) UpdateAndSwap(newBackup PackedMulti) error {
 		return fmt.Errorf("unable to close file: %w", err)
 	}

+	if !b.deleteOldBackup {


should also update the docs in UpdateAndSwap about this new behavior.

yyforyongyu · 2025-01-08T07:27:18Z

chanbackup/backupfile_test.go

@@ -94,7 +94,7 @@ func TestUpdateAndSwap(t *testing.T) {
 		},
 	}
 	for i, testCase := range testCases {
-		backupFile := NewMultiFile(testCase.fileName)
+		backupFile := NewMultiFile(testCase.fileName, false)


think this test should also be updated to check the new behavior, maybe a new test TestUpdateAndSwapWithArchive.

The test is in the next commit ade9d50, I will squash it into the first commit.

In this commit, we first check if a previous backup file exists, if it does we copy it to archive folder before replacing it with a new backup file.

In this commit, we add the --disable-backup-archive with a default as false. When set to true then previous channel backup file will not be archived but replaced.

Abdulkbk marked this pull request as ready for review November 1, 2024 11:49

Abdulkbk mentioned this pull request Nov 1, 2024

chanbackup/[feature]: add archive mode for channel back ups #8906

Open

Abdulkbk force-pushed the archive-channel-backups branch from bd7fb87 to 71ee590 Compare November 24, 2024 15:38

MPins reviewed Dec 7, 2024

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chanbackup/backupfile_test.go Show resolved Hide resolved

Abdulkbk force-pushed the archive-channel-backups branch from 71ee590 to 375e0fb Compare December 22, 2024 16:46

MPins approved these changes Jan 6, 2025

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chanbackup/backupfile_test.go Show resolved Hide resolved

Abdulkbk changed the title ~~chanbackup: archive old channel backups~~ chanbackup: archive old channel backup files Jan 7, 2025

Abdulkbk force-pushed the archive-channel-backups branch from 375e0fb to ade9d50 Compare January 7, 2025 04:13

yyforyongyu added this to the v0.19.0 milestone Jan 8, 2025

yyforyongyu added enhancement Improvements to existing features / behaviour SCB Related to static channel backup size/kilo medium, proper context needed, less than 1000 lines labels Jan 8, 2025

yyforyongyu requested changes Jan 8, 2025

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Abdulkbk added 4 commits January 13, 2025 13:40

chanbackup: archive old channel backups

b038ddd

In this commit, we first check if a previous backup file exists, if it does we copy it to archive folder before replacing it with a new backup file.

lnd+chanbackup: add lnd config flag

ca669b9

In this commit, we add the --disable-backup-archive with a default as false. When set to true then previous channel backup file will not be archived but replaced.

chanbackup: test archiving chan backups

817168a

docs: add release note

c5a1f13

Abdulkbk force-pushed the archive-channel-backups branch from 7dd1be4 to c5a1f13 Compare January 13, 2025 19:42

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	// DefaultChanBackupDirName is the default name of the directory that
	// DefaultChanBackupArchiveDirName is the default name of the directory that

chanbackup: archive old channel backup files #9232

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chanbackup: archive old channel backup files #9232

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