Passing a full duration as retention period is more flexible

cmd/backup/config.go

@@ -38,6 +38,7 @@ type Config struct {
 	BackupArchive                 string          `split_words:"true" default:"/archive"`
 	BackupCronExpression          string          `split_words:"true" default:"@daily"`
 	BackupRetentionDays           int32           `split_words:"true" default:"-1"`
+	BackupRetentionPeriod         time.Duration   `split_words:"true"`
 	BackupPruningLeeway           time.Duration   `split_words:"true" default:"1m"`
 	BackupPruningPrefix           string          `split_words:"true"`
 	BackupStopContainerLabel      string          `split_words:"true"`

cmd/backup/prune_backups.go

@@ -17,11 +17,18 @@ import (
 // the given configuration. In case the given configuration would delete all
 // backups, it does nothing instead and logs a warning.
 func (s *script) pruneBackups() error {
-	if s.c.BackupRetentionDays < 0 {
+	if s.c.BackupRetentionDays < 0 && s.c.BackupRetentionPeriod == 0 {
 		return nil
 	}
 
-	deadline := time.Now().AddDate(0, 0, -int(s.c.BackupRetentionDays)).Add(s.c.BackupPruningLeeway)
+	var deadline time.Time
+	if s.c.BackupRetentionPeriod != 0 {
+		deadline = time.Now().Add(-s.c.BackupRetentionPeriod)
+	} else {
+		s.logger.Warn("Using BACKUP_RETENTION_DAYS has been deprecated and will be removed in the next major version. Please use BACKUP_RETENTION_PERIOD instead.")
+		deadline = time.Now().AddDate(0, 0, -int(s.c.BackupRetentionDays))
+	}
+	deadline = deadline.Add(s.c.BackupPruningLeeway)
 
 	eg := errgroup.Group{}
 	for _, backend := range s.storages {

cmd/backup/script.go

@@ -225,6 +225,10 @@ func (s *script) init() error {
 		s.storages = append(s.storages, dropboxBackend)
 	}
 
+	if s.c.BackupRetentionDays > 0 && s.c.BackupRetentionPeriod > 0 {
+		return errwrap.Wrap(nil, "both BACKUP_RETENTION_DAYS and BACKUP_RETENTION_PERIOD were configured, which are mutually exclusive")
+	}
+
 	if s.c.EmailNotificationRecipient != "" {
 		emailURL := fmt.Sprintf(
 			"smtp://%s:%s@%s:%d/?from=%s&to=%s",

docs/how-tos/automatically-prune-old-backups.md

@@ -7,7 +7,8 @@ nav_order: 3
 
 # Automatically prune old backups
 
-When `BACKUP_RETENTION_DAYS` is configured, the command will check if there are any archives in the remote storage backend(s) or local archive that are older than the given retention value and rotate these backups away.
+When `BACKUP_RETENTION_PERIOD` is configured, the command will check if there are any archives in the remote storage backend(s) or local archive that are older than the given retention value and rotate these backups away.
+The value is a duration as per Go's [`time.ParseDuration`][duration].
 
 {: .note }
 Be aware that this mechanism looks at __all files in the target bucket or archive__, which means that other files that are older than the given deadline are deleted as well.
@@ -23,7 +24,7 @@ services:
     environment:
       BACKUP_FILENAME: backup-%Y-%m-%dT%H-%M-%S.tar.gz
       BACKUP_PRUNING_PREFIX: backup-
-      BACKUP_RETENTION_DAYS: '7'
+      BACKUP_RETENTION_PERIOD: '168h'
     volumes:
       - ${HOME}/backups:/archive
       - data:/backup/my-app-backup:ro
@@ -32,3 +33,5 @@ services:
 volumes:
   data:
 ```
+
+[duration]: https://pkg.go.dev/time#ParseDuration

docs/recipes/index.md

@@ -280,7 +280,7 @@ services:
       AWS_SECRET_ACCESS_KEY: wJalrXUtnFEMI/K7MDENG/bPxRfiCYEXAMPLEKEY
       BACKUP_FILENAME: backup-%Y-%m-%dT%H-%M-%S.tar.gz
       BACKUP_PRUNING_PREFIX: backup-
-      BACKUP_RETENTION_DAYS: 7
+      BACKUP_RETENTION_PERIOD: 168h
     volumes:
       - data:/backup/my-app-backup:ro
       - /var/run/docker.sock:/var/run/docker.sock:ro

docs/reference/index.md

@@ -312,9 +312,10 @@ You can populate below template according to your requirements and use it as you
 # removal to certain files.
 
 # Define this value to enable automatic rotation of old backups. The value
-# declares the number of days for which a backup is kept.
+# declares the duration for which a backup is kept. It is formatted as per
+# https://pkg.go.dev/time#ParseDuration
 
-# BACKUP_RETENTION_DAYS="7"
+# BACKUP_RETENTION_PERIOD="168h"
 
 # In case the duration a backup takes fluctuates noticeably in your setup
 # you can adjust this setting to make sure there are no race conditions