Add support for Azure Blob Storage (#171)

* Scaffold Azure storage backend that does nothing yet

* Implement copy for Azure Blob Storage

* Set up automated testing for Azure Storage

* Implement pruning for Azure blob storage

* Add documentation for Azure Blob Storage

* Add support for remote path

* Add azure to notifications doc

* Tidy go.mod file

* Allow use of managed identity credential

* Use volume in tests

* Auto append trailing slash to endpoint if needed, clarify docs, tidy mod file

README.md

@@ -7,7 +7,7 @@
 Backup Docker volumes locally or to any S3, WebDAV or SSH compatible storage.
 
 The [offen/docker-volume-backup](https://hub.docker.com/r/offen/docker-volume-backup) Docker image can be used as a lightweight (below 15MB) sidecar container to an existing Docker setup.
-It handles __recurring or one-off backups of Docker volumes__ to a __local directory__, __any S3, WebDAV or SSH compatible storage (or any combination) and rotates away old backups__ if configured. It also supports __encrypting your backups using GPG__ and __sending notifications for failed backup runs__.
+It handles __recurring or one-off backups of Docker volumes__ to a __local directory__, __any S3, WebDAV, Azure Blob Storage or SSH compatible storage (or any combination) and rotates away old backups__ if configured. It also supports __encrypting your backups using GPG__ and __sending notifications for failed backup runs__.
 
 <!-- MarkdownTOC -->
 
@@ -41,6 +41,7 @@ It handles __recurring or one-off backups of Docker volumes__ to a __local direc
   - [Backing up to MinIO \(using Docker secrets\)](#backing-up-to-minio-using-docker-secrets)
   - [Backing up to WebDAV](#backing-up-to-webdav)
   - [Backing up to SSH](#backing-up-to-ssh)
+  - [Backing up to Azure Blob Storage](#backing-up-to-azure-blob-storage)
   - [Backing up locally](#backing-up-locally)
   - [Backing up to AWS S3 as well as locally](#backing-up-to-aws-s3-as-well-as-locally)
   - [Running on a custom cron schedule](#running-on-a-custom-cron-schedule)
@@ -304,6 +305,25 @@ You can populate below template according to your requirements and use it as you
 
 # SSH_IDENTITY_PASSPHRASE="pass"
 
+# The credential's account name when using Azure Blob Storage. This has to be
+# set when using Azure Blob Storage.
+
+# AZURE_STORAGE_ACCOUNT_NAME="account-name"
+
+# The credential's primary account key when using Azure Blob Storage. If this
+# is not given, the command tries to fall back to using a managed identity.
+
+# AZURE_STORAGE_PRIMARY_ACCOUNT_KEY="<xxx>"
+
+# The container name when using Azure Blob Storage.
+
+# AZURE_STORAGE_CONTAINER_NAME="container-name"
+
+# The service endpoint when using Azure Blob Storage. This is a template that
+# can be passed the account name as shown in the default value below.
+
+# AZURE_STORAGE_ENDPOINT="https://{{ .AccountName }}.blob.core.windows.net/"
+
 # In addition to storing backups remotely, you can also keep local copies.
 # Pass a container-local path to store your backups if needed. You also need to
 # mount a local folder or Docker volume into that location (`/archive`
@@ -1079,6 +1099,27 @@ volumes:
   data:
 ```
 
+### Backing up to Azure Blob Storage
+
+```yml
+version: '3'
+
+services:
+  # ... define other services using the `data` volume here
+  backup:
+    image: offen/docker-volume-backup:v2
+    environment:
+      AZURE_STORAGE_CONTAINER_NAME: backup-container
+      AZURE_STORAGE_ACCOUNT_NAME: account-name
+      AZURE_STORAGE_PRIMARY_ACCOUNT_KEY: Eby8vdM02xNOcqFlqUwJPLlmEtlCDXJ1OUzFT50uSRZ6IFsuFq2UVErCz4I6tq/K1SZFPTOtr/KBHBeksoGMGw==
+    volumes:
+      - data:/backup/my-app-backup:ro
+      - /var/run/docker.sock:/var/run/docker.sock:ro
+
+volumes:
+  data:
+```
+
 ### Backing up locally
 
 ```yml

cmd/backup/config.go

@@ -63,6 +63,11 @@ type Config struct {
 	ExecLabel                     string        `split_words:"true"`
 	ExecForwardOutput             bool          `split_words:"true"`
 	LockTimeout                   time.Duration `split_words:"true" default:"60m"`
+	AzureStorageAccountName       string        `split_words:"true"`
+	AzureStoragePrimaryAccountKey string        `split_words:"true"`
+	AzureStorageContainerName     string        `split_words:"true"`
+	AzureStoragePath              string        `split_words:"true"`
+	AzureStorageEndpoint          string        `split_words:"true" default:"https://{{ .AccountName }}.blob.core.windows.net/"`
 }
 
 func (c *Config) resolveSecret(envVar string, secretPath string) (string, error) {

cmd/backup/script.go

@@ -15,6 +15,7 @@ import (
 	"time"
 
 	"github.com/offen/docker-volume-backup/internal/storage"
+	"github.com/offen/docker-volume-backup/internal/storage/azure"
 	"github.com/offen/docker-volume-backup/internal/storage/local"
 	"github.com/offen/docker-volume-backup/internal/storage/s3"
 	"github.com/offen/docker-volume-backup/internal/storage/ssh"
@@ -76,6 +77,7 @@ func newScript() (*script, error) {
 				"WebDAV": {},
 				"SSH":    {},
 				"Local":  {},
+				"Azure":  {},
 			},
 		},
 	}
@@ -189,6 +191,21 @@ func newScript() (*script, error) {
 		s.storages = append(s.storages, localBackend)
 	}
 
+	if s.c.AzureStorageAccountName != "" {
+		azureConfig := azure.Config{
+			ContainerName:     s.c.AzureStorageContainerName,
+			AccountName:       s.c.AzureStorageAccountName,
+			PrimaryAccountKey: s.c.AzureStoragePrimaryAccountKey,
+			Endpoint:          s.c.AzureStorageEndpoint,
+			RemotePath:        s.c.AzureStoragePath,
+		}
+		azureBackend, err := azure.NewStorageBackend(azureConfig, logFunc)
+		if err != nil {
+			return nil, err
+		}
+		s.storages = append(s.storages, azureBackend)
+	}
+
 	if s.c.EmailNotificationRecipient != "" {
 		emailURL := fmt.Sprintf(
 			"smtp://%s:%s@%s:%d/?from=%s&to=%s",

docs/NOTIFICATION-TEMPLATES.md

@@ -25,7 +25,7 @@ Here is a list of all data passed to the template:
     * `FullPath`: full path of the backup file (e.g. `/archive/backup-2022-02-11T01-00-00.tar.gz`)
     * `Size`: size in bytes of the backup file
   * `Storages`: object that holds stats about each storage
-    * `Local`, `S3`, `WebDAV` or `SSH`:
+    * `Local`, `S3`, `WebDAV`, `Azure` or `SSH`:
       * `Total`: total number of backup files
       * `Pruned`: number of backup files that were deleted due to pruning rule
       * `PruneErrors`: number of backup files that were unable to be pruned

go.mod

@@ -3,6 +3,8 @@ module github.com/offen/docker-volume-backup
 go 1.19
 
 require (
+	github.com/Azure/azure-sdk-for-go/sdk/azidentity v1.2.0
+	github.com/Azure/azure-sdk-for-go/sdk/storage/azblob v0.6.1
 	github.com/containrrr/shoutrrr v0.5.2
 	github.com/cosiner/argv v0.1.0
 	github.com/docker/docker v20.10.11+incompatible
@@ -19,6 +21,9 @@ require (
 )
 
 require (
+	github.com/Azure/azure-sdk-for-go/sdk/azcore v1.1.4 // indirect
+	github.com/Azure/azure-sdk-for-go/sdk/internal v1.0.1 // indirect
+	github.com/AzureAD/microsoft-authentication-library-for-go v0.7.0 // indirect
 	github.com/Microsoft/go-winio v0.5.2 // indirect
 	github.com/containerd/containerd v1.6.6 // indirect
 	github.com/docker/distribution v2.7.1+incompatible // indirect
@@ -28,6 +33,7 @@ require (
 	github.com/fatih/color v1.10.0 // indirect
 	github.com/fsnotify/fsnotify v1.4.9 // indirect
 	github.com/gogo/protobuf v1.3.2 // indirect
+	github.com/golang-jwt/jwt/v4 v4.4.2 // indirect
 	github.com/golang/protobuf v1.5.2 // indirect
 	github.com/google/uuid v1.3.0 // indirect
 	github.com/gorilla/mux v1.7.3 // indirect
@@ -36,6 +42,7 @@ require (
 	github.com/klauspost/cpuid/v2 v2.2.1 // indirect
 	github.com/kr/fs v0.1.0 // indirect
 	github.com/kr/text v0.2.0 // indirect
+	github.com/kylelemons/godebug v1.1.0 // indirect
 	github.com/mattn/go-colorable v0.1.8 // indirect
 	github.com/mattn/go-isatty v0.0.12 // indirect
 	github.com/minio/md5-simd v1.1.2 // indirect
@@ -50,6 +57,7 @@ require (
 	github.com/onsi/gomega v1.10.3 // indirect
 	github.com/opencontainers/go-digest v1.0.0 // indirect
 	github.com/opencontainers/image-spec v1.0.3-0.20211202183452-c5a74bcca799 // indirect
+	github.com/pkg/browser v0.0.0-20210115035449-ce105d075bb4 // indirect
 	github.com/pkg/errors v0.9.1 // indirect
 	github.com/rs/xid v1.4.0 // indirect
 	golang.org/x/net v0.2.0 // indirect

go.sum

@@ -1,7 +1,17 @@
 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=
+github.com/Azure/azure-sdk-for-go/sdk/azcore v1.1.4 h1:pqrAR74b6EoR4kcxF7L7Wg2B8Jgil9UUZtMvxhEFqWo=
+github.com/Azure/azure-sdk-for-go/sdk/azcore v1.1.4/go.mod h1:uGG2W01BaETf0Ozp+QxxKJdMBNRWPdstHG0Fmdwn1/U=
+github.com/Azure/azure-sdk-for-go/sdk/azidentity v1.2.0 h1:t/W5MYAuQy81cvM8VUNfRLzhtKpXhVUAN7Cd7KVbTyc=
+github.com/Azure/azure-sdk-for-go/sdk/azidentity v1.2.0/go.mod h1:NBanQUfSWiWn3QEpWDTCU0IjBECKOYvl2R8xdRtMtiM=
+github.com/Azure/azure-sdk-for-go/sdk/internal v1.0.1 h1:XUNQ4mw+zJmaA2KXzP9JlQiecy1SI+Eog7xVkPiqIbg=
+github.com/Azure/azure-sdk-for-go/sdk/internal v1.0.1/go.mod h1:eWRD7oawr1Mu1sLCawqVc0CUiF43ia3qQMxLscsKQ9w=
+github.com/Azure/azure-sdk-for-go/sdk/storage/azblob v0.6.1 h1:YvQv9Mz6T8oR5ypQOL6erY0Z5t71ak1uHV4QFokCOZk=
+github.com/Azure/azure-sdk-for-go/sdk/storage/azblob v0.6.1/go.mod h1:c6WvOhtmjNUWbLfOG1qxM/q0SPvQNSVJvolm+C52dIU=
 github.com/Azure/go-ansiterm v0.0.0-20170929234023-d6e3b3328b78 h1:w+iIsaOQNcT7OZ575w+acHgRric5iCyQh+xv+KJ4HB8=
 github.com/Azure/go-ansiterm v0.0.0-20170929234023-d6e3b3328b78/go.mod h1:LmzpDX56iTiv29bbRTIsUNlaFfuhWRQBWjQdVyAevI8=
+github.com/AzureAD/microsoft-authentication-library-for-go v0.7.0 h1:VgSJlZH5u0k2qxSpqyghcFQKmvYckj46uymKK5XzkBM=
+github.com/AzureAD/microsoft-authentication-library-for-go v0.7.0/go.mod h1:BDJ5qMFKx9DugEg3+uQSDCdbYPr5s9vBTrL9P8TpqOU=
 github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03qcyfWMU=
 github.com/Microsoft/go-winio v0.5.2 h1:a9IhgEQBCUEk6QCdml9CiJGhAws+YwffDHEMp1VMrpA=
 github.com/Microsoft/go-winio v0.5.2/go.mod h1:WpS1mjBmmwHBEWmogvA2mj8546UReBk4v8QkMxJ6pZY=
@@ -48,6 +58,7 @@ github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/dgrijalva/jwt-go v3.2.0+incompatible/go.mod h1:E3ru+11k8xSBh+hMPgOLZmtrrCbhqsmaPHjLKYnJCaQ=
 github.com/dgryski/go-sip13 v0.0.0-20181026042036-e10d5fee7954/go.mod h1:vAd38F8PWV+bWy6jNmig1y/TA+kYO4g3RSRF0IAv0no=
+github.com/dnaeon/go-vcr v1.1.0 h1:ReYa/UBrRyQdant9B4fNHGoCNKw6qh6P0fsdGmZpR7c=
 github.com/docker/distribution v2.7.1+incompatible h1:a5mlkVzth6W5A4fOsS3D2EO5BUmsJpcB+cRlLU7cSug=
 github.com/docker/distribution v2.7.1+incompatible/go.mod h1:J2gT2udsDAN96Uj4KfcMRqY0/ypR+oyYUYmja8H+y+w=
 github.com/docker/docker v20.10.11+incompatible h1:OqzI/g/W54LczvhnccGqniFoQghHx3pklbLuhfXpqGo=
@@ -94,6 +105,8 @@ github.com/gogo/protobuf v1.1.1/go.mod h1:r8qH/GZQm5c6nD/R0oafs1akxWv10x8SbQlK7a
 github.com/gogo/protobuf v1.2.1/go.mod h1:hp+jE20tsWTFYpLwKvXlhS1hjn+gTNwPg2I6zVXpSg4=
 github.com/gogo/protobuf v1.3.2 h1:Ov1cvc58UF3b5XjBnZv7+opcTcQFZebYjWzi34vdm4Q=
 github.com/gogo/protobuf v1.3.2/go.mod h1:P1XiOD3dCwIKUDQYPy72D8LYyHL2YPYrpS2s69NZV8Q=
+github.com/golang-jwt/jwt/v4 v4.4.2 h1:rcc4lwaZgFMCZ5jxF9ABolDcIHdBytAFgqFPbSJQAYs=
+github.com/golang-jwt/jwt/v4 v4.4.2/go.mod h1:m21LjoU+eqJr34lmDMbreY2eSTRJ1cv77w39/MY0Ch0=
 github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b/go.mod h1:SBH7ygxi8pfUlaOkMMuAQtPIUF8ecWP5IEl/CR7VP2Q=
 github.com/golang/groupcache v0.0.0-20190129154638-5b532d6fd5ef/go.mod h1:cIg4eruTrX1D+g88fzRXU5OdNfaM+9IcxsU14FzY7Hc=
 github.com/golang/mock v1.1.1/go.mod h1:oTYuIxOrZwtPieC+H1uAHpcLFnEyAGVDL/k47Jfbm0A=
@@ -174,6 +187,8 @@ github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
 github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
 github.com/kr/text v0.2.0 h1:5Nx0Ya0ZqY2ygV366QzturHI13Jq95ApcVaJBhpS+AY=
 github.com/kr/text v0.2.0/go.mod h1:eLer722TekiGuMkidMxC/pM04lWEeraHUUmBw8l2grE=
+github.com/kylelemons/godebug v1.1.0 h1:RPNrshWIDI6G2gRW9EHilWtl7Z6Sb1BR0xunSBf0SNc=
+github.com/kylelemons/godebug v1.1.0/go.mod h1:9/0rRGxNHcop5bhtWyNeEfOS8JIWk580+fNqagV/RAw=
 github.com/leekchan/timeutil v0.0.0-20150802142658-28917288c48d h1:2puqoOQwi3Ai1oznMOsFIbifm6kIfJaLLyYzWD4IzTs=
 github.com/leekchan/timeutil v0.0.0-20150802142658-28917288c48d/go.mod h1:hO90vCP2x3exaSH58BIAowSKvV+0OsY21TtzuFGHON4=
 github.com/leodido/go-urn v1.2.0/go.mod h1:+8+nEpDfqqsY+g338gtMEUOtuK+4dEMhiQEgxpxOKII=
@@ -244,6 +259,8 @@ github.com/otiai10/mint v1.3.3 h1:7JgpsBaN0uMkyju4tbYHu0mnM55hNKVYLsXmwr15NQI=
 github.com/otiai10/mint v1.3.3/go.mod h1:/yxELlJQ0ufhjUwhshSj+wFjZ78CnZ48/1wtmBH1OTc=
 github.com/pelletier/go-toml v1.2.0/go.mod h1:5z9KED0ma1S8pY6P1sdut58dfprrGBbd/94hg7ilaic=
 github.com/pelletier/go-toml v1.7.0/go.mod h1:vwGMzjaWMwyfHwgIBhI2YUM4fB6nL6lVAvS1LBMMhTE=
+github.com/pkg/browser v0.0.0-20210115035449-ce105d075bb4 h1:Qj1ukM4GlMWXNdMBuXcXfz/Kw9s1qm0CLY32QxuSImI=
+github.com/pkg/browser v0.0.0-20210115035449-ce105d075bb4/go.mod h1:N6UoU20jOqggOuDwUaBQpluzLNDqif3kq9z2wpdYEfQ=
 github.com/pkg/errors v0.8.0/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pkg/errors v0.8.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=
@@ -296,8 +313,8 @@ github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXf
 github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
 github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
 github.com/stretchr/testify v1.5.1/go.mod h1:5W2xD1RspED5o8YsWQXVCued0rvSQ+mT+I5cxcmMvtA=
-github.com/stretchr/testify v1.7.0 h1:nwc3DEeHmmLAfoZucVR881uASk0Mfjw8xYJ99tb5CcY=
 github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+github.com/stretchr/testify v1.7.1 h1:5TQK59W5E3v0r2duFAb7P95B6hEeOyEnHRa8MjYSMTY=
 github.com/studio-b12/gowebdav v0.0.0-20220128162035-c7b1ff8a5e62 h1:b2nJXyPCa9HY7giGM+kYcnQ71m14JnGdQabMPmyt++8=
 github.com/studio-b12/gowebdav v0.0.0-20220128162035-c7b1ff8a5e62/go.mod h1:bHA7t77X/QFExdeAnDzK6vKM34kEZAcE1OX4MfiwjkE=
 github.com/subosito/gotenv v1.2.0/go.mod h1:N0PQaV/YGNqwC0u51sEeR/aUtSLEXKX9iv69rRypqCw=

internal/storage/azure/azure.go

@@ -0,0 +1,160 @@
+// Copyright 2022 - Offen Authors <hioffen@posteo.de>
+// SPDX-License-Identifier: MPL-2.0
+
+package azure
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"sync"
+	"text/template"
+	"time"
+
+	"github.com/Azure/azure-sdk-for-go/sdk/azidentity"
+	"github.com/Azure/azure-sdk-for-go/sdk/storage/azblob"
+	"github.com/Azure/azure-sdk-for-go/sdk/storage/azblob/container"
+	"github.com/offen/docker-volume-backup/internal/storage"
+	"github.com/offen/docker-volume-backup/internal/utilities"
+)
+
+type azureBlobStorage struct {
+	*storage.StorageBackend
+	client        *azblob.Client
+	containerName string
+}
+
+// Config contains values that define the configuration of an Azure Blob Storage.
+type Config struct {
+	AccountName       string
+	ContainerName     string
+	PrimaryAccountKey string
+	Endpoint          string
+	RemotePath        string
+}
+
+// NewStorageBackend creates and initializes a new Azure Blob Storage backend.
+func NewStorageBackend(opts Config, logFunc storage.Log) (storage.Backend, error) {
+	endpointTemplate, err := template.New("endpoint").Parse(opts.Endpoint)
+	if err != nil {
+		return nil, fmt.Errorf("NewStorageBackend: error parsing endpoint template: %w", err)
+	}
+	var ep bytes.Buffer
+	if err := endpointTemplate.Execute(&ep, opts); err != nil {
+		return nil, fmt.Errorf("NewStorageBackend: error executing endpoint template: %w", err)
+	}
+	normalizedEndpoint := fmt.Sprintf("%s/", strings.TrimSuffix(ep.String(), "/"))
+
+	var client *azblob.Client
+	if opts.PrimaryAccountKey != "" {
+		cred, err := azblob.NewSharedKeyCredential(opts.AccountName, opts.PrimaryAccountKey)
+		if err != nil {
+			return nil, fmt.Errorf("NewStorageBackend: error creating shared key Azure credential: %w", err)
+		}
+
+		client, err = azblob.NewClientWithSharedKeyCredential(normalizedEndpoint, cred, nil)
+		if err != nil {
+			return nil, fmt.Errorf("NewStorageBackend: error creating Azure client: %w", err)
+		}
+	} else {
+		cred, err := azidentity.NewManagedIdentityCredential(nil)
+		if err != nil {
+			return nil, fmt.Errorf("NewStorageBackend: error creating managed identity credential: %w", err)
+		}
+		client, err = azblob.NewClient(normalizedEndpoint, cred, nil)
+		if err != nil {
+			return nil, fmt.Errorf("NewStorageBackend: error creating Azure client: %w", err)
+		}
+	}
+
+	storage := azureBlobStorage{
+		client:        client,
+		containerName: opts.ContainerName,
+		StorageBackend: &storage.StorageBackend{
+			DestinationPath: opts.RemotePath,
+			Log:             logFunc,
+		},
+	}
+	return &storage, nil
+}
+
+// Name returns the name of the storage backend
+func (b *azureBlobStorage) Name() string {
+	return "Azure"
+}
+
+// Copy copies the given file to the storage backend.
+func (b *azureBlobStorage) Copy(file string) error {
+	fileReader, err := os.Open(file)
+	if err != nil {
+		return fmt.Errorf("(*azureBlobStorage).Copy: error opening file %s: %w", file, err)
+	}
+	_, err = b.client.UploadStream(
+		context.Background(),
+		b.containerName,
+		filepath.Join(b.DestinationPath, filepath.Base(file)),
+		fileReader,
+		nil,
+	)
+	if err != nil {
+		return fmt.Errorf("(*azureBlobStorage).Copy: error uploading file %s: %w", file, err)
+	}
+	return nil
+}
+
+// Prune rotates away backups according to the configuration and provided
+// deadline for the Azure Blob storage backend.
+func (b *azureBlobStorage) Prune(deadline time.Time, pruningPrefix string) (*storage.PruneStats, error) {
+	lookupPrefix := filepath.Join(b.DestinationPath, pruningPrefix)
+	pager := b.client.NewListBlobsFlatPager(b.containerName, &container.ListBlobsFlatOptions{
+		Prefix: &lookupPrefix,
+	})
+	var matches []string
+	var totalCount uint
+	for pager.More() {
+		resp, err := pager.NextPage(context.Background())
+		if err != nil {
+			return nil, fmt.Errorf("(*azureBlobStorage).Prune: error paging over blobs: %w", err)
+		}
+		for _, v := range resp.Segment.BlobItems {
+			totalCount++
+			if v.Properties.LastModified.Before(deadline) {
+				matches = append(matches, *v.Name)
+			}
+		}
+	}
+
+	stats := storage.PruneStats{
+		Total:  totalCount,
+		Pruned: uint(len(matches)),
+	}
+
+	if err := b.DoPrune(b.Name(), len(matches), int(totalCount), "Azure Blob Storage backup(s)", func() error {
+		wg := sync.WaitGroup{}
+		wg.Add(len(matches))
+		var errors []error
+
+		for _, match := range matches {
+			name := match
+			go func() {
+				_, err := b.client.DeleteBlob(context.Background(), b.containerName, name, nil)
+				if err != nil {
+					errors = append(errors, err)
+				}
+				wg.Done()
+			}()
+		}
+		wg.Wait()
+		if len(errors) != 0 {
+			return utilities.Join(errors...)
+		}
+		return nil
+	}); err != nil {
+		return &stats, err
+	}
+
+	return &stats, nil
+}

test/azure/docker-compose.yml

@@ -0,0 +1,58 @@
+version: '3'
+
+services:
+  storage:
+    image: mcr.microsoft.com/azure-storage/azurite
+    volumes:
+      - azurite_backup_data:/data
+    command: azurite-blob --blobHost 0.0.0.0 --blobPort 10000 --location /data
+    healthcheck:
+        test: nc 127.0.0.1 10000 -z
+        interval: 1s
+        retries: 30
+
+  az_cli:
+    image: mcr.microsoft.com/azure-cli
+    volumes:
+      - ./local:/dump
+    command:
+      - /bin/sh
+      - -c
+      - |
+          az storage container create --name test-container
+    depends_on:
+      storage:
+        condition: service_healthy
+    environment:
+      AZURE_STORAGE_CONNECTION_STRING: DefaultEndpointsProtocol=http;AccountName=devstoreaccount1;AccountKey=Eby8vdM02xNOcqFlqUwJPLlmEtlCDXJ1OUzFT50uSRZ6IFsuFq2UVErCz4I6tq/K1SZFPTOtr/KBHBeksoGMGw==;BlobEndpoint=http://storage:10000/devstoreaccount1;
+
+  backup:
+    image: offen/docker-volume-backup:${TEST_VERSION:-canary}
+    hostname: hostnametoken
+    restart: always
+    environment:
+      AZURE_STORAGE_ACCOUNT_NAME: devstoreaccount1
+      AZURE_STORAGE_PRIMARY_ACCOUNT_KEY: Eby8vdM02xNOcqFlqUwJPLlmEtlCDXJ1OUzFT50uSRZ6IFsuFq2UVErCz4I6tq/K1SZFPTOtr/KBHBeksoGMGw==
+      AZURE_STORAGE_CONTAINER_NAME: test-container
+      AZURE_STORAGE_ENDPOINT: http://storage:10000/{{ .AccountName }}/
+      AZURE_STORAGE_PATH: 'path/to/backup'
+      BACKUP_FILENAME: test.tar.gz
+      BACKUP_CRON_EXPRESSION: 0 0 5 31 2 ?
+      BACKUP_RETENTION_DAYS: ${BACKUP_RETENTION_DAYS:-7}
+      BACKUP_PRUNING_LEEWAY: 5s
+      BACKUP_PRUNING_PREFIX: test
+    volumes:
+      - 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:
+  azurite_backup_data:
+    name: azurite_backup_data
+  app_data:

test/azure/run.sh

@@ -0,0 +1,40 @@
+#!/bin/sh
+
+set -e
+
+cd "$(dirname "$0")"
+. ../util.sh
+current_test=$(basename $(pwd))
+
+docker-compose up -d
+sleep 5
+
+# A symlink for a known file in the volume is created so the test can check
+# whether symlinks are preserved on backup.
+docker-compose exec backup backup
+
+sleep 5
+
+expect_running_containers "3"
+
+docker-compose run --rm az_cli \
+  az storage blob download -f /dump/test.tar.gz -c test-container -n path/to/backup/test.tar.gz
+tar -xvf ./local/test.tar.gz -C /tmp && test -f /tmp/backup/app_data/offen.db
+
+pass "Found relevant files in untared remote backups."
+
+# The second part of this test checks if backups get deleted when the retention
+# is set to 0 days (which it should not as it would mean all backups get deleted)
+# TODO: find out if we can test actual deletion without having to wait for a day
+BACKUP_RETENTION_DAYS="0" docker-compose up -d
+sleep 5
+
+docker-compose exec backup backup
+
+docker-compose run --rm az_cli \
+  az storage blob download -f /dump/test.tar.gz -c test-container -n path/to/backup/test.tar.gz
+test -f ./local/test.tar.gz
+
+pass "Remote backups have not been deleted."
+
+docker-compose down --volumes