Exclude legacy docs page from navigation

GPG is known to have usability issues and is generally cumbersome to
use. age [0] is a modern alternative to GPG that is designed by a
cryptographer that has worked and continues to work on Golang's crypto
packages for years.

Allowing age to be used to encrypt backups dramatically simplifies the
backup process.

[0]: https://age-encryption.org/

cmd/backup/command.go

@@ -36,9 +36,6 @@ func (c *command) runAsCommand() error {
 	}
 
 	for _, config := range configurations {
-		if err := config.validate(); err != nil {
-			return errwrap.Wrap(err, "error validating config")
-		}
 		if err := runScript(config); err != nil {
 			return errwrap.Wrap(err, "error running script")
 		}
@@ -104,12 +101,6 @@ func (c *command) schedule(strategy configStrategy) error {
 	}
 
 	for _, cfg := range configurations {
-		if err := cfg.validate(); err != nil {
-			return errwrap.Wrap(
-				err,
-				fmt.Sprintf("error validating config for schedule %s", cfg.BackupCronExpression),
-			)
-		}
 		config := cfg
 		id, err := c.cr.AddFunc(config.BackupCronExpression, func() {
 			c.logger.Info(

cmd/backup/config.go

@@ -12,91 +12,85 @@ import (
 	"strconv"
 	"time"
 
-	"github.com/Azure/azure-sdk-for-go/sdk/storage/azblob/blob"
 	"github.com/offen/docker-volume-backup/internal/errwrap"
 )
 
 // Config holds all configuration values that are expected to be set
 // by users.
 type Config struct {
-	AwsS3BucketName               string                 `split_words:"true"`
+	AwsS3BucketName               string          `split_words:"true"`
-	AwsS3Path                     string                 `split_words:"true"`
+	AwsS3Path                     string          `split_words:"true"`
-	AwsEndpoint                   string                 `split_words:"true" default:"s3.amazonaws.com"`
+	AwsEndpoint                   string          `split_words:"true" default:"s3.amazonaws.com"`
-	AwsEndpointProto              string                 `split_words:"true" default:"https"`
+	AwsEndpointProto              string          `split_words:"true" default:"https"`
-	AwsEndpointInsecure           bool                   `split_words:"true"`
+	AwsEndpointInsecure           bool            `split_words:"true"`
-	AwsEndpointCACert             CertDecoder            `envconfig:"AWS_ENDPOINT_CA_CERT"`
+	AwsEndpointCACert             CertDecoder     `envconfig:"AWS_ENDPOINT_CA_CERT"`
-	AwsStorageClass               string                 `split_words:"true"`
+	AwsStorageClass               string          `split_words:"true"`
-	AwsAccessKeyID                string                 `envconfig:"AWS_ACCESS_KEY_ID"`
+	AwsAccessKeyID                string          `envconfig:"AWS_ACCESS_KEY_ID"`
-	AwsSecretAccessKey            string                 `split_words:"true"`
+	AwsSecretAccessKey            string          `split_words:"true"`
-	AwsIamRoleEndpoint            string                 `split_words:"true"`
+	AwsIamRoleEndpoint            string          `split_words:"true"`
-	AwsPartSize                   int64                  `split_words:"true"`
+	AwsPartSize                   int64           `split_words:"true"`
-	BackupCompression             CompressionType        `split_words:"true" default:"gz"`
+	BackupCompression             CompressionType `split_words:"true" default:"gz"`
-	GzipParallelism               WholeNumber            `split_words:"true" default:"1"`
+	GzipParallelism               WholeNumber     `split_words:"true" default:"1"`
-	BackupSources                 string                 `split_words:"true" default:"/backup"`
+	BackupSources                 string          `split_words:"true" default:"/backup"`
-	BackupFilename                string                 `split_words:"true" default:"backup-%Y-%m-%dT%H-%M-%S.{{ .Extension }}"`
+	BackupFilename                string          `split_words:"true" default:"backup-%Y-%m-%dT%H-%M-%S.{{ .Extension }}"`
-	BackupFilenameExpand          bool                   `split_words:"true"`
+	BackupFilenameExpand          bool            `split_words:"true"`
-	BackupLatestSymlink           string                 `split_words:"true"`
+	BackupLatestSymlink           string          `split_words:"true"`
-	BackupArchive                 string                 `split_words:"true" default:"/archive"`
+	BackupArchive                 string          `split_words:"true" default:"/archive"`
-	BackupCronExpression          string                 `split_words:"true" default:"@daily"`
+	BackupCronExpression          string          `split_words:"true" default:"@daily"`
-	BackupRetentionDays           int32                  `split_words:"true" default:"-1"`
+	BackupRetentionDays           int32           `split_words:"true" default:"-1"`
-	BackupPruningLeeway           time.Duration          `split_words:"true" default:"1m"`
+	BackupPruningLeeway           time.Duration   `split_words:"true" default:"1m"`
-	BackupPruningPrefix           string                 `split_words:"true"`
+	BackupPruningPrefix           string          `split_words:"true"`
-	BackupStopContainerLabel      string                 `split_words:"true"`
+	BackupStopContainerLabel      string          `split_words:"true"`
-	BackupStopDuringBackupLabel   string                 `split_words:"true" default:"true"`
+	BackupStopDuringBackupLabel   string          `split_words:"true" default:"true"`
-	BackupStopServiceTimeout      time.Duration          `split_words:"true" default:"5m"`
+	BackupStopServiceTimeout      time.Duration   `split_words:"true" default:"5m"`
-	BackupFromSnapshot            bool                   `split_words:"true"`
+	BackupFromSnapshot            bool            `split_words:"true"`
-	BackupExcludeRegexp           RegexpDecoder          `split_words:"true"`
+	BackupExcludeRegexp           RegexpDecoder   `split_words:"true"`
-	BackupSkipBackendsFromPrune   []string               `split_words:"true"`
+	BackupSkipBackendsFromPrune   []string        `split_words:"true"`
-	GpgPassphrase                 string                 `split_words:"true"`
+	GpgPassphrase                 string          `split_words:"true"`
-	GpgPublicKeyRing              string                 `split_words:"true"`
+	GpgPublicKeyRing              string          `split_words:"true"`
-	NotificationURLs              []string               `envconfig:"NOTIFICATION_URLS"`
+	AgePassphrase                 string          `split_words:"true"`
-	NotificationLevel             string                 `split_words:"true" default:"error"`
+	AgePublicKeys                 []string        `split_words:"true"`
-	EmailNotificationRecipient    string                 `split_words:"true"`
+	NotificationURLs              []string        `envconfig:"NOTIFICATION_URLS"`
-	EmailNotificationSender       string                 `split_words:"true" default:"noreply@nohost"`
+	NotificationLevel             string          `split_words:"true" default:"error"`
-	EmailSMTPHost                 string                 `envconfig:"EMAIL_SMTP_HOST"`
+	EmailNotificationRecipient    string          `split_words:"true"`
-	EmailSMTPPort                 int                    `envconfig:"EMAIL_SMTP_PORT" default:"587"`
+	EmailNotificationSender       string          `split_words:"true" default:"noreply@nohost"`
-	EmailSMTPUsername             string                 `envconfig:"EMAIL_SMTP_USERNAME"`
+	EmailSMTPHost                 string          `envconfig:"EMAIL_SMTP_HOST"`
-	EmailSMTPPassword             string                 `envconfig:"EMAIL_SMTP_PASSWORD"`
+	EmailSMTPPort                 int             `envconfig:"EMAIL_SMTP_PORT" default:"587"`
-	WebdavUrl                     string                 `split_words:"true"`
+	EmailSMTPUsername             string          `envconfig:"EMAIL_SMTP_USERNAME"`
-	WebdavUrlInsecure             bool                   `split_words:"true"`
+	EmailSMTPPassword             string          `envconfig:"EMAIL_SMTP_PASSWORD"`
-	WebdavPath                    string                 `split_words:"true" default:"/"`
+	WebdavUrl                     string          `split_words:"true"`
-	WebdavUsername                string                 `split_words:"true"`
+	WebdavUrlInsecure             bool            `split_words:"true"`
-	WebdavPassword                string                 `split_words:"true"`
+	WebdavPath                    string          `split_words:"true" default:"/"`
-	SSHHostName                   string                 `split_words:"true"`
+	WebdavUsername                string          `split_words:"true"`
-	SSHPort                       string                 `split_words:"true" default:"22"`
+	WebdavPassword                string          `split_words:"true"`
-	SSHUser                       string                 `split_words:"true"`
+	SSHHostName                   string          `split_words:"true"`
-	SSHPassword                   string                 `split_words:"true"`
+	SSHPort                       string          `split_words:"true" default:"22"`
-	SSHIdentityFile               string                 `split_words:"true" default:"/root/.ssh/id_rsa"`
+	SSHUser                       string          `split_words:"true"`
-	SSHIdentityPassphrase         string                 `split_words:"true"`
+	SSHPassword                   string          `split_words:"true"`
-	SSHRemotePath                 string                 `split_words:"true"`
+	SSHIdentityFile               string          `split_words:"true" default:"/root/.ssh/id_rsa"`
-	ExecLabel                     string                 `split_words:"true"`
+	SSHIdentityPassphrase         string          `split_words:"true"`
-	ExecForwardOutput             bool                   `split_words:"true"`
+	SSHRemotePath                 string          `split_words:"true"`
-	LockTimeout                   time.Duration          `split_words:"true" default:"60m"`
+	ExecLabel                     string          `split_words:"true"`
-	AzureStorageAccountName       string                 `split_words:"true"`
+	ExecForwardOutput             bool            `split_words:"true"`
-	AzureStoragePrimaryAccountKey string                 `split_words:"true"`
+	LockTimeout                   time.Duration   `split_words:"true" default:"60m"`
-	AzureStorageConnectionString  string                 `split_words:"true"`
+	AzureStorageAccountName       string          `split_words:"true"`
-	AzureStorageContainerName     string                 `split_words:"true"`
+	AzureStoragePrimaryAccountKey string          `split_words:"true"`
-	AzureStoragePath              string                 `split_words:"true"`
+	AzureStorageConnectionString  string          `split_words:"true"`
-	AzureStorageEndpoint          string                 `split_words:"true" default:"https://{{ .AccountName }}.blob.core.windows.net/"`
+	AzureStorageContainerName     string          `split_words:"true"`
-	AzureStorageAccessTier        AzureStorageAccessTier `split_words:"true"`
+	AzureStoragePath              string          `split_words:"true"`
-	DropboxEndpoint               string                 `split_words:"true" default:"https://api.dropbox.com/"`
+	AzureStorageEndpoint          string          `split_words:"true" default:"https://{{ .AccountName }}.blob.core.windows.net/"`
-	DropboxOAuth2Endpoint         string                 `envconfig:"DROPBOX_OAUTH2_ENDPOINT" default:"https://api.dropbox.com/"`
+	AzureStorageAccessTier        string          `split_words:"true"`
-	DropboxRefreshToken           string                 `split_words:"true"`
+	DropboxEndpoint               string          `split_words:"true" default:"https://api.dropbox.com/"`
-	DropboxAppKey                 string                 `split_words:"true"`
+	DropboxOAuth2Endpoint         string          `envconfig:"DROPBOX_OAUTH2_ENDPOINT" default:"https://api.dropbox.com/"`
-	DropboxAppSecret              string                 `split_words:"true"`
+	DropboxRefreshToken           string          `split_words:"true"`
-	DropboxRemotePath             string                 `split_words:"true"`
+	DropboxAppKey                 string          `split_words:"true"`
-	DropboxConcurrencyLevel       NaturalNumber          `split_words:"true" default:"6"`
+	DropboxAppSecret              string          `split_words:"true"`
+	DropboxRemotePath             string          `split_words:"true"`
+	DropboxConcurrencyLevel       NaturalNumber   `split_words:"true" default:"6"`
 	source                        string
 	additionalEnvVars             map[string]string
 }
 
-func (c *Config) validate() error {
-	if c.AzureStoragePrimaryAccountKey != "" && c.AzureStorageConnectionString != "" {
-		return errwrap.Wrap(nil, "using azure primary account key and connection string are mutually exclusive")
-	}
-	return nil
-}
-
 type CompressionType string
 
 func (c *CompressionType) Decode(v string) error {
@@ -188,30 +182,6 @@ func (n *WholeNumber) Int() int {
 	return int(*n)
 }
 
-type AzureStorageAccessTier string
-
-func (t *AzureStorageAccessTier) Decode(v string) error {
-	if v == "" {
-		*t = ""
-		return nil
-	}
-	for _, a := range blob.PossibleAccessTierValues() {
-		if string(a) == v {
-			*t = AzureStorageAccessTier(v)
-			return nil
-		}
-	}
-	return errwrap.Wrap(nil, fmt.Sprintf("%s is not a possible access tier value", v))
-}
-
-func (t *AzureStorageAccessTier) AccessTier() *blob.AccessTier {
-	if *t == "" {
-		return nil
-	}
-	a := blob.AccessTier(*t)
-	return &a
-}
-
 type envVarLookup struct {
 	ok    bool
 	key   string

cmd/backup/encrypt_archive.go

@@ -11,109 +11,191 @@ import (
 	"os"
 	"path"
 
+	"filippo.io/age"
 	"github.com/ProtonMail/go-crypto/openpgp/armor"
 	openpgp "github.com/ProtonMail/go-crypto/openpgp/v2"
 	"github.com/offen/docker-volume-backup/internal/errwrap"
 )
 
-func (s *script) encryptAsymmetrically(outFile *os.File) (io.WriteCloser, func() error, error) {
+func countTrue(b ...bool) int {
-
+	c := int(0)
-	entityList, err := openpgp.ReadArmoredKeyRing(bytes.NewReader([]byte(s.c.GpgPublicKeyRing)))
+	for _, v := range b {
-	if err != nil {
+		if v {
-		return nil, nil, errwrap.Wrap(err, "error parsing armored keyring")
+			c++
-	}
-
-	armoredWriter, err := armor.Encode(outFile, "PGP MESSAGE", nil)
-	if err != nil {
-		return nil, nil, errwrap.Wrap(err, "error preparing encryption")
-	}
-
-	_, name := path.Split(s.file)
-	dst, err := openpgp.Encrypt(armoredWriter, entityList, nil, nil, &openpgp.FileHints{
-		FileName: name,
-	}, nil)
-	if err != nil {
-		return nil, nil, err
-	}
-
-	return dst, func() error {
-		if err := dst.Close(); err != nil {
-			return err
 		}
-		return armoredWriter.Close()
-	}, err
-}
-
-func (s *script) encryptSymmetrically(outFile *os.File) (io.WriteCloser, func() error, error) {
-
-	_, name := path.Split(s.file)
-	dst, err := openpgp.SymmetricallyEncrypt(outFile, []byte(s.c.GpgPassphrase), &openpgp.FileHints{
-		FileName: name,
-	}, nil)
-	if err != nil {
-		return nil, nil, err
 	}
-
+	return c
-	return dst, dst.Close, nil
 }
 
 // encryptArchive encrypts the backup file using PGP and the configured passphrase or publickey(s).
 // In case no passphrase or publickey is given it returns early, leaving the backup file
 // untouched.
 func (s *script) encryptArchive() error {
-
+	useGPGSymmetric := s.c.GpgPassphrase != ""
-	var encrypt func(outFile *os.File) (io.WriteCloser, func() error, error)
+	useGPGAsymmetric := s.c.GpgPublicKeyRing != ""
-	var cleanUpErr error
+	useAgeSymmetric := s.c.AgePassphrase != ""
-
+	useAgeAsymmetric := len(s.c.AgePublicKeys) > 0
-	switch {
+	switch nconfigured := countTrue(
-	case s.c.GpgPassphrase != "" && s.c.GpgPublicKeyRing != "":
+		useGPGSymmetric,
-		return errwrap.Wrap(nil, "error in selecting asymmetric and symmetric encryption methods: conflicting env vars are set")
+		useGPGAsymmetric,
-	case s.c.GpgPassphrase != "":
+		useAgeSymmetric,
-		encrypt = s.encryptSymmetrically
+		useAgeAsymmetric,
-	case s.c.GpgPublicKeyRing != "":
+	); nconfigured {
-		encrypt = s.encryptAsymmetrically
+	case 0:
-	default:
 		return nil
+	case 1:
+		// ok!
+	default:
+		return fmt.Errorf(
+			"error in selecting archive encryption method: expected 0 or 1 to be configured, %d methods are configured",
+			nconfigured,
+		)
 	}
 
-	gpgFile := fmt.Sprintf("%s.gpg", s.file)
+	if useGPGSymmetric {
+		return s.encryptWithGPGSymmetric()
+	} else if useGPGAsymmetric {
+		return s.encryptWithGPGAsymmetric()
+	} else if useAgeSymmetric || useAgeAsymmetric {
+		ar, err := s.getConfiguredAgeRecipients()
+		if err != nil {
+			return errwrap.Wrap(err, "failed to get configured age recipients")
+		}
+		return s.encryptWithAge(ar)
+	}
+	return nil
+}
+
+func (s *script) getConfiguredAgeRecipients() ([]age.Recipient, error) {
+	if s.c.AgePassphrase == "" && len(s.c.AgePublicKeys) == 0 {
+		return nil, fmt.Errorf("no age recipients configured")
+	}
+	recipients := []age.Recipient{}
+	if len(s.c.AgePublicKeys) > 0 {
+		for _, pk := range s.c.AgePublicKeys {
+			pkr, err := age.ParseX25519Recipient(pk)
+			if err != nil {
+				return nil, errwrap.Wrap(err, "failed to parse age public key")
+			}
+			recipients = append(recipients, pkr)
+		}
+	}
+	if s.c.AgePassphrase != "" {
+		if len(recipients) != 0 {
+			return nil, fmt.Errorf("age encryption must only be enabled via passphrase or public key, not both")
+		}
+
+		r, err := age.NewScryptRecipient(s.c.AgePassphrase)
+		if err != nil {
+			return nil, errwrap.Wrap(err, "failed to create scrypt identity from age passphrase")
+		}
+		recipients = append(recipients, r)
+	}
+	return recipients, nil
+}
+
+func (s *script) encryptWithAge(rec []age.Recipient) error {
+	return s.doEncrypt("age", func(ciphertextWriter io.Writer) (io.WriteCloser, error) {
+		return age.Encrypt(ciphertextWriter, rec...)
+	})
+}
+
+func (s *script) encryptWithGPGSymmetric() error {
+	return s.doEncrypt("gpg", func(ciphertextWriter io.Writer) (io.WriteCloser, error) {
+		_, name := path.Split(s.file)
+		return openpgp.SymmetricallyEncrypt(ciphertextWriter, []byte(s.c.GpgPassphrase), &openpgp.FileHints{
+			FileName: name,
+		}, nil)
+	})
+}
+
+type closeAllWriter struct {
+	io.Writer
+	closers []io.Closer
+}
+
+func (c *closeAllWriter) Close() (err error) {
+	for _, cl := range c.closers {
+		err = errors.Join(err, cl.Close())
+	}
+	return
+}
+
+var _ io.WriteCloser = (*closeAllWriter)(nil)
+
+func (s *script) encryptWithGPGAsymmetric() error {
+	return s.doEncrypt("gpg", func(ciphertextWriter io.Writer) (_ io.WriteCloser, outerr error) {
+		entityList, err := openpgp.ReadArmoredKeyRing(bytes.NewReader([]byte(s.c.GpgPublicKeyRing)))
+		if err != nil {
+			return nil, errwrap.Wrap(err, "error parsing armored keyring")
+		}
+
+		armoredWriter, err := armor.Encode(ciphertextWriter, "PGP MESSAGE", nil)
+		if err != nil {
+			return nil, errwrap.Wrap(err, "error preparing encryption")
+		}
+		defer func() {
+			if outerr != nil {
+				_ = armoredWriter.Close()
+			}
+		}()
+
+		_, name := path.Split(s.file)
+		encWriter, err := openpgp.Encrypt(armoredWriter, entityList, nil, nil, &openpgp.FileHints{
+			FileName: name,
+		}, nil)
+		if err != nil {
+			return nil, err
+		}
+		return &closeAllWriter{
+			Writer:  encWriter,
+			closers: []io.Closer{encWriter, armoredWriter},
+		}, nil
+	})
+}
+
+func (s *script) doEncrypt(
+	extension string,
+	encryptor func(ciphertextWriter io.Writer) (io.WriteCloser, error),
+) (outerr error) {
+	encFile := fmt.Sprintf("%s.%s", s.file, extension)
 	s.registerHook(hookLevelPlumbing, func(error) error {
-		if err := remove(gpgFile); err != nil {
+		if err := remove(encFile); err != nil {
-			return errwrap.Wrap(err, "error removing gpg file")
+			return errwrap.Wrap(err, "error removing encrypted file")
 		}
 		s.logger.Info(
-			fmt.Sprintf("Removed GPG file `%s`.", gpgFile),
+			fmt.Sprintf("Removed encrypted file `%s`.", encFile),
 		)
 		return nil
 	})
 
-	outFile, err := os.Create(gpgFile)
+	outFile, err := os.Create(encFile)
 	if err != nil {
 		return errwrap.Wrap(err, "error opening out file")
 	}
 	defer func() {
 		if err := outFile.Close(); err != nil {
-			cleanUpErr = errors.Join(cleanUpErr, errwrap.Wrap(err, "error closing out file"))
+			outerr = errors.Join(outerr, errwrap.Wrap(err, "error closing out file"))
 		}
 	}()
 
-	dst, dstCloseCallback, err := encrypt(outFile)
+	dst, err := encryptor(outFile)
 	if err != nil {
 		return errwrap.Wrap(err, "error encrypting backup file")
 	}
 	defer func() {
-		if err := dstCloseCallback(); err != nil {
+		if err := dst.Close(); err != nil {
-			cleanUpErr = errors.Join(cleanUpErr, errwrap.Wrap(err, "error closing encrypted backup file"))
+			outerr = errors.Join(outerr, errwrap.Wrap(err, "error closing encrypted backup file"))
 		}
 	}()
 
 	src, err := os.Open(s.file)
 	if err != nil {
-		return errwrap.Wrap(err, fmt.Sprintf("error opening backup file `%s`", s.file))
+		return errwrap.Wrap(err, fmt.Sprintf("error opening backup file %q", s.file))
 	}
 	defer func() {
 		if err := src.Close(); err != nil {
-			cleanUpErr = errors.Join(cleanUpErr, errwrap.Wrap(err, "error closing backup file"))
+			outerr = errors.Join(outerr, errwrap.Wrap(err, "error closing backup file"))
 		}
 	}()
 
@@ -121,9 +203,10 @@ func (s *script) encryptArchive() error {
 		return errwrap.Wrap(err, "error writing ciphertext to file")
 	}
 
-	s.file = gpgFile
+	s.file = encFile
 	s.logger.Info(
-		fmt.Sprintf("Encrypted backup using gpg, saving as `%s`.", s.file),
+		fmt.Sprintf("Encrypted backup using %q, saving as %q", extension, s.file),
 	)
-	return cleanUpErr
+
+	return
 }

cmd/backup/script.go

@@ -199,7 +199,7 @@ func (s *script) init() error {
 			Endpoint:          s.c.AzureStorageEndpoint,
 			RemotePath:        s.c.AzureStoragePath,
 			ConnectionString:  s.c.AzureStorageConnectionString,
-			AccessTier:        s.c.AzureStorageAccessTier.AccessTier(),
+			AccessTier:        s.c.AzureStorageAccessTier,
 		}
 		azureBackend, err := azure.NewStorageBackend(azureConfig, logFunc)
 		if err != nil {

docs/how-tos/encrypt-backups-using-gpg.md

@@ -3,15 +3,7 @@ title: Encrypt backups using GPG
 layout: default
 parent: How Tos
 nav_order: 7
+nav_exclude: true
 ---
 
-# Encrypt backups using GPG
+See: [Encrypt Backups](encrypt-backups)
-
-The image supports encrypting backups using GPG out of the box.
-In case a `GPG_PASSPHRASE` or `GPG_PUBLIC_KEY_RING` environment variable is set, the backup archive will be encrypted using the given key and saved as a `.gpg` file instead.
-
-Assuming you have `gpg` installed, you can decrypt such a backup using (your OS will prompt for the passphrase before decryption can happen):
-
-```console
-gpg -o backup.tar.gz -d backup.tar.gz.gpg
-```

docs/how-tos/encrypt-backups.md

@@ -0,0 +1,28 @@
+---
+title: Encrypting backups
+layout: default
+parent: How Tos
+nav_order: 7
+---
+
+# Encrypting backups
+
+The image supports encrypting backups using one of two available methods: **GPG** or **[age](https://age-encryption.org/)**
+
+## Using GPG encryption
+
+In case a `GPG_PASSPHRASE` or `GPG_PUBLIC_KEY_RING` environment variable is set, the backup archive will be encrypted using the given key and saved as a `.gpg` file instead.
+
+Assuming you have `gpg` installed, you can decrypt such a backup using (your OS will prompt for the passphrase before decryption can happen):
+
+```console
+gpg -o backup.tar.gz -d backup.tar.gz.gpg
+```
+
+## Using age encryption
+
+age allows backups to be encrypted with either a symmetric key (password) or a public key. One of those options are available for use.
+
+Given `AGE_PASSPHRASE` being provided, the backup archive will be encrypted with the passphrase and saved as a `.age` file instead. Refer to age documentation for how to properly decrypt.
+
+Given `AGE_PUBLIC_KEYS` being provided (allowing multiple by separating each public key with `,`), the backup archive will be encrypted with the provided public keys. It will also result in the archive being saved as a `.age` file.

go.mod

@@ -3,6 +3,7 @@ module github.com/offen/docker-volume-backup
 go 1.22
 
 require (
+	filippo.io/age v1.2.0
 	github.com/Azure/azure-sdk-for-go/sdk/azidentity v1.7.0
 	github.com/Azure/azure-sdk-for-go/sdk/storage/azblob v1.4.0
 	github.com/containrrr/shoutrrr v0.8.0
@@ -13,7 +14,7 @@ require (
 	github.com/joho/godotenv v1.5.1
 	github.com/klauspost/compress v1.17.9
 	github.com/leekchan/timeutil v0.0.0-20150802142658-28917288c48d
-	github.com/minio/minio-go/v7 v7.0.74
+	github.com/minio/minio-go/v7 v7.0.75
 	github.com/offen/envconfig v1.5.0
 	github.com/otiai10/copy v1.14.0
 	github.com/pkg/sftp v1.13.6

go.sum

@@ -1,3 +1,5 @@
+c2sp.org/CCTV/age v0.0.0-20240306222714-3ec4d716e805 h1:u2qwJeEvnypw+OCPUHmoZE3IqwfuN5kgDfo5MLzpNM0=
+c2sp.org/CCTV/age v0.0.0-20240306222714-3ec4d716e805/go.mod h1:FomMrUJ2Lxt5jCLmZkG3FHa72zUprnhd3v/Z18Snm4w=
 cloud.google.com/go v0.26.0/go.mod h1:aQUYkXzVsufM+DwF1aE+0xfcU+56JwCaLick0ClmMTw=
 cloud.google.com/go v0.34.0/go.mod h1:aQUYkXzVsufM+DwF1aE+0xfcU+56JwCaLick0ClmMTw=
 cloud.google.com/go v0.38.0/go.mod h1:990N+gfupTy94rShfmMCWGDn0LpTmnzTp2qbd1dvSRU=
@@ -31,6 +33,8 @@ cloud.google.com/go/storage v1.6.0/go.mod h1:N7U0C8pVQ/+NIKOBQyamJIeKQKkZ+mxpohl
 cloud.google.com/go/storage v1.8.0/go.mod h1:Wv1Oy7z6Yz3DshWRJFhqM/UCfaWIRTdp0RXyy7KQOVs=
 cloud.google.com/go/storage v1.10.0/go.mod h1:FLPqc6j+Ki4BU591ie1oL6qBQGu2Bl/tZ9ullr3+Kg0=
 dmitri.shuralyov.com/gpu/mtl v0.0.0-20190408044501-666a987793e9/go.mod h1:H6x//7gZCb22OMCxBHrMx7a5I7Hp++hsVxbQ4BYO7hU=
+filippo.io/age v1.2.0 h1:vRDp7pUMaAJzXNIWJVAZnEf/Dyi4Vu4wI8S1LBzufhE=
+filippo.io/age v1.2.0/go.mod h1:JL9ew2lTN+Pyft4RiNGguFfOpewKwSHm5ayKD/A4004=
 github.com/Azure/azure-sdk-for-go/sdk/azcore v1.13.0 h1:GJHeeA2N7xrG3q30L2UXDyuWRzDM900/65j70wcM4Ww=
 github.com/Azure/azure-sdk-for-go/sdk/azcore v1.13.0/go.mod h1:l38EPgmsp71HHLq9j7De57JcKOWPyhrsW1Awm1JS6K0=
 github.com/Azure/azure-sdk-for-go/sdk/azidentity v1.7.0 h1:tfLQ34V6F7tVSwoTf/4lH5sE0o6eCJuNDTmH09nDpbc=
@@ -208,8 +212,8 @@ github.com/mattn/go-isatty v0.0.20 h1:xfD0iDuEKnDkl03q4limB+vH+GxLEtL/jb4xVJSWWE
 github.com/mattn/go-isatty v0.0.20/go.mod h1:W+V8PltTTMOvKvAeJH7IuucS94S2C6jfK/D7dTCTo3Y=
 github.com/minio/md5-simd v1.1.2 h1:Gdi1DZK69+ZVMoNHRXJyNcxrMA4dSxoYHZSQbirFg34=
 github.com/minio/md5-simd v1.1.2/go.mod h1:MzdKDxYpY2BT9XQFocsiZf/NKVtR7nkE4RoEpN+20RM=
-github.com/minio/minio-go/v7 v7.0.74 h1:fTo/XlPBTSpo3BAMshlwKL5RspXRv9us5UeHEGYCFe0=
+github.com/minio/minio-go/v7 v7.0.75 h1:0uLrB6u6teY2Jt+cJUVi9cTvDRuBKWSRzSAcznRkwlE=
-github.com/minio/minio-go/v7 v7.0.74/go.mod h1:qydcVzV8Hqtj1VtEocfxbmVFa2siu6HGa+LDEPogjD8=
+github.com/minio/minio-go/v7 v7.0.75/go.mod h1:qydcVzV8Hqtj1VtEocfxbmVFa2siu6HGa+LDEPogjD8=
 github.com/moby/docker-image-spec v1.3.1 h1:jMKff3w6PgbfSa69GfNg+zN/XLhfXJGnEx3Nl2EsFP0=
 github.com/moby/docker-image-spec v1.3.1/go.mod h1:eKmb5VW8vQEh/BAr2yvVNvuiJuY6UIocYsFu/DxxRpo=
 github.com/moby/term v0.0.0-20200312100748-672ec06f55cd h1:aY7OQNf2XqY/JQ6qREWamhI/81os/agb2BAGpcx5yWI=
@@ -485,8 +489,8 @@ golang.org/x/tools v0.0.0-20200804011535-6c149bb5ef0d/go.mod h1:njjCfa9FT2d7l9Bc
 golang.org/x/tools v0.0.0-20200825202427-b303f430e36d/go.mod h1:njjCfa9FT2d7l9Bc6FUM5FLjQPp3cFF28FI3qnDFljA=
 golang.org/x/tools v0.0.0-20210106214847-113979e3529a/go.mod h1:emZCQorbCU4vsT4fOWvOPXz4eW1wZW4PmDk9uLelYpA=
 golang.org/x/tools v0.1.12/go.mod h1:hNGJHUnrk76NpqgfD5Aqm5Crs+Hm0VOH/i9J2+nxYbc=
-golang.org/x/tools v0.21.1-0.20240508182429-e35e4ccd0d2d h1:vU5i/LfpvrRCpgM/VPfJLg5KjxD3E+hfT1SH+d9zLwg=
+golang.org/x/tools v0.22.0 h1:gqSGLZqv+AI9lIQzniJ0nZDRG5GBPsSi+DRNHWNz6yA=
-golang.org/x/tools v0.21.1-0.20240508182429-e35e4ccd0d2d/go.mod h1:aiJjzUbINMkxbQROHiO6hDPo2LHcIPhhQsa9DLh0yGk=
+golang.org/x/tools v0.22.0/go.mod h1:aCwcsjqvq7Yqt6TNyX7QMU2enbQ/Gt0bo6krSeEri+c=
 golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=

internal/storage/azure/azure.go

@@ -39,11 +39,15 @@ type Config struct {
 	ConnectionString  string
 	Endpoint          string
 	RemotePath        string
-	AccessTier        *blob.AccessTier
+	AccessTier        string
 }
 
 // NewStorageBackend creates and initializes a new Azure Blob Storage backend.
 func NewStorageBackend(opts Config, logFunc storage.Log) (storage.Backend, error) {
+	if opts.PrimaryAccountKey != "" && opts.ConnectionString != "" {
+		return nil, errwrap.Wrap(nil, "using primary account key and connection string are mutually exclusive")
+	}
+
 	endpointTemplate, err := template.New("endpoint").Parse(opts.Endpoint)
 	if err != nil {
 		return nil, errwrap.Wrap(err, "error parsing endpoint template")
@@ -81,12 +85,26 @@ func NewStorageBackend(opts Config, logFunc storage.Log) (storage.Backend, error
 		}
 	}
 
+	var uploadStreamOptions *blockblob.UploadStreamOptions
+	if opts.AccessTier != "" {
+		var found bool
+		for _, t := range blob.PossibleAccessTierValues() {
+			if string(t) == opts.AccessTier {
+				found = true
+				uploadStreamOptions = &blockblob.UploadStreamOptions{
+					AccessTier: &t,
+				}
+			}
+		}
+		if !found {
+			return nil, errwrap.Wrap(nil, fmt.Sprintf("%s is not a possible access tier value", opts.AccessTier))
+		}
+	}
+
 	storage := azureBlobStorage{
-		client: client,
+		client:              client,
-		uploadStreamOptions: &blockblob.UploadStreamOptions{
+		uploadStreamOptions: uploadStreamOptions,
-			AccessTier: opts.AccessTier,
+		containerName:       opts.ContainerName,
-		},
-		containerName: opts.ContainerName,
 		StorageBackend: &storage.StorageBackend{
 			DestinationPath: opts.RemotePath,
 			Log:             logFunc,

test/Dockerfile

@@ -1,8 +1,10 @@
 FROM docker:27-dind
 
 RUN apk add \
+  age \
   coreutils \
   curl \
+  expect \
   gpg \
   gpg-agent \
   jq \

test/age-passphrase/docker-compose.yml

@@ -0,0 +1,24 @@
+services:
+  backup:
+    image: offen/docker-volume-backup:${TEST_VERSION:-canary}
+    restart: always
+    environment:
+      BACKUP_CRON_EXPRESSION: 0 0 5 31 2 ?
+      BACKUP_FILENAME: test.tar.gz
+      BACKUP_LATEST_SYMLINK: test-latest.tar.gz.age
+      BACKUP_RETENTION_DAYS: ${BACKUP_RETENTION_DAYS:-7}
+      AGE_PASSPHRASE: "Dance.0Tonight.Go.Typical"
+    volumes:
+      - ${LOCAL_DIR:-./local}:/archive
+      - app_data:/backup/app_data:ro
+      - /var/run/docker.sock:/var/run/docker.sock
+
+  offen:
+    image: offen/offen:latest
+    labels:
+      - docker-volume-backup.stop-during-backup=true
+    volumes:
+      - app_data:/var/opt/offen
+
+volumes:
+  app_data:

test/age-passphrase/run.sh

@@ -0,0 +1,39 @@
+#!/bin/sh
+
+set -e
+
+cd "$(dirname "$0")"
+. ../util.sh
+current_test=$(basename "$(pwd)")
+
+export LOCAL_DIR="$(mktemp -d)"
+
+docker compose up -d --quiet-pull
+sleep 5
+
+docker compose exec backup backup
+
+expect_running_containers "2"
+
+TMP_DIR=$(mktemp -d)
+
+# complex usage of expect(1) due to age not have a way to programmatically
+# provide the passphrase
+expect -i <<EOL
+spawn age --decrypt -o "$LOCAL_DIR/decrypted.tar.gz" "$LOCAL_DIR/test.tar.gz.age"
+expect -exact "Enter passphrase: "
+send -- "Dance.0Tonight.Go.Typical\r"
+sleep 1
+EOL
+tar -xf "$LOCAL_DIR/decrypted.tar.gz" -C "$TMP_DIR"
+
+if [ ! -f "$TMP_DIR/backup/app_data/offen.db" ]; then
+  fail "Could not find expected file in untared archive."
+fi
+rm -vf "$LOCAL_DIR/decrypted.tar.gz"
+
+pass "Found relevant files in decrypted and untared local backup."
+
+if [ ! -L "$LOCAL_DIR/test-latest.tar.gz.age" ]; then
+  fail "Could not find local symlink to latest encrypted backup."
+fi

test/age-publickey/.gitignore

@@ -0,0 +1 @@
+pk-*.txt

test/age-publickey/docker-compose.yml

@@ -0,0 +1,24 @@
+services:
+  backup:
+    image: offen/docker-volume-backup:${TEST_VERSION:-canary}
+    restart: always
+    environment:
+      BACKUP_CRON_EXPRESSION: 0 0 5 31 2 ?
+      BACKUP_FILENAME: test.tar.gz
+      BACKUP_LATEST_SYMLINK: test-latest.tar.gz.age
+      BACKUP_RETENTION_DAYS: ${BACKUP_RETENTION_DAYS:-7}
+      AGE_PUBLIC_KEYS: "${BACKUP_AGE_PUBLIC_KEYS}"
+    volumes:
+      - ${LOCAL_DIR:-./local}:/archive
+      - app_data:/backup/app_data:ro
+      - /var/run/docker.sock:/var/run/docker.sock
+
+  offen:
+    image: offen/offen:latest
+    labels:
+      - docker-volume-backup.stop-during-backup=true
+    volumes:
+      - app_data:/var/opt/offen
+
+volumes:
+  app_data:

test/age-publickey/run.sh

@@ -0,0 +1,43 @@
+#!/bin/sh
+
+set -e
+
+cd "$(dirname "$0")"
+. ../util.sh
+current_test=$(basename "$(pwd)")
+
+export LOCAL_DIR="$(mktemp -d)"
+
+age-keygen >"$LOCAL_DIR/pk-a.txt"
+PK_A="$(grep -E 'public key' <"$LOCAL_DIR/pk-a.txt" | cut -d: -f2 | xargs)"
+age-keygen >"$LOCAL_DIR/pk-b.txt"
+PK_B="$(grep -E 'public key' <"$LOCAL_DIR/pk-b.txt" | cut -d: -f2 | xargs)"
+
+export BACKUP_AGE_PUBLIC_KEYS="$PK_A,$PK_B"
+
+docker compose up -d --quiet-pull
+sleep 5
+
+docker compose exec backup backup
+
+expect_running_containers "2"
+
+do_decrypt() {
+  TMP_DIR=$(mktemp -d)
+  age --decrypt -i "$1" -o "$LOCAL_DIR/decrypted.tar.gz" "$LOCAL_DIR/test.tar.gz.age"
+  tar -xf "$LOCAL_DIR/decrypted.tar.gz" -C "$TMP_DIR"
+
+  if [ ! -f "$TMP_DIR/backup/app_data/offen.db" ]; then
+    fail "Could not find expected file in untared archive."
+  fi
+  rm -vf "$LOCAL_DIR/decrypted.tar.gz"
+
+  pass "Found relevant files in decrypted and untared local backup."
+
+  if [ ! -L "$LOCAL_DIR/test-latest.tar.gz.age" ]; then
+    fail "Could not find local symlink to latest encrypted backup."
+  fi
+}
+
+do_decrypt "$LOCAL_DIR/pk-a.txt"
+do_decrypt "$LOCAL_DIR/pk-b.txt"