Move cron scheduling inside application (#338)

* Move cron scheduling inside application

* Make envvar a fallback and check for errors

* Panic significantly less

* propagate error out of runBackup

* Add structured logging

* FIx error propagation to exit

* Enable the new scheduler by default

* Review fixes

* Added docs and better error propagation

Dockerfile

@@ -18,4 +18,4 @@ RUN apk add --no-cache ca-certificates
 COPY --from=builder /app/cmd/backup/backup /usr/bin/backup
 COPY --chmod=755 ./entrypoint.sh /root/
 
-ENTRYPOINT ["/root/entrypoint.sh"]
+ENTRYPOINT ["/usr/bin/backup", "-foreground"]

cmd/backup/config.go

@@ -34,6 +34,7 @@ type Config struct {
 	BackupFilenameExpand          bool            `split_words:"true"`
 	BackupLatestSymlink           string          `split_words:"true"`
 	BackupArchive                 string          `split_words:"true" default:"/archive"`
+	BackupCronExpression          string          `split_words:"true" default:"@daily"`
 	BackupRetentionDays           int32           `split_words:"true" default:"-1"`
 	BackupPruningLeeway           time.Duration   `split_words:"true" default:"1m"`
 	BackupPruningPrefix           string          `split_words:"true"`

cmd/backup/config_provider.go

@@ -0,0 +1,81 @@
+// Copyright 2021-2022 - Offen Authors <hioffen@posteo.de>
+// SPDX-License-Identifier: MPL-2.0
+
+package main
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"github.com/joho/godotenv"
+	"github.com/offen/envconfig"
+)
+
+// envProxy is a function that mimics os.LookupEnv but can read values from any other source
+type envProxy func(string) (string, bool)
+
+func loadConfig(lookup envProxy) (*Config, error) {
+	envconfig.Lookup = func(key string) (string, bool) {
+		value, okValue := lookup(key)
+		location, okFile := lookup(key + "_FILE")
+
+		switch {
+		case okValue && !okFile: // only value
+			return value, true
+		case !okValue && okFile: // only file
+			contents, err := os.ReadFile(location)
+			if err != nil {
+				return "", false
+			}
+			return string(contents), true
+		case okValue && okFile: // both
+			return "", false
+		default: // neither, ignore
+			return "", false
+		}
+	}
+
+	var c = &Config{}
+	if err := envconfig.Process("", c); err != nil {
+		return nil, fmt.Errorf("failed to process configuration values, error: %w", err)
+	}
+
+	return c, nil
+}
+
+func loadEnvVars() (*Config, error) {
+	return loadConfig(os.LookupEnv)
+}
+
+func loadEnvFiles(directory string) ([]*Config, error) {
+	items, err := os.ReadDir(directory)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil, err
+		}
+		return nil, fmt.Errorf("failed to read files from env directory, error: %w", err)
+	}
+
+	var cs = make([]*Config, 0)
+	for _, item := range items {
+		if !item.IsDir() {
+			p := filepath.Join(directory, item.Name())
+			envFile, err := godotenv.Read(p)
+			if err != nil {
+				return nil, fmt.Errorf("error reading config file %s, error: %w", p, err)
+			}
+			lookup := func(key string) (string, bool) {
+				val, ok := envFile[key]
+				return val, ok
+			}
+			c, err := loadConfig(lookup)
+			if err != nil {
+				return nil, fmt.Errorf("error loading config from file %s, error: %w", p, err)
+			}
+			cs = append(cs, c)
+		}
+	}
+
+	return cs, nil
+}

cmd/backup/main.go

@@ -4,21 +4,33 @@
 package main
 
 import (
+	"flag"
 	"fmt"
+	"log/slog"
 	"os"
+	"os/signal"
+	"syscall"
+
+	"github.com/robfig/cron/v3"
 )
 
-func main() {
-	s, err := newScript()
+func runScript(c *Config) (ret error) {
+	s, err := newScript(c)
 	if err != nil {
-		panic(err)
+		return err
 	}
 
 	unlock, err := s.lock("/var/lock/dockervolumebackup.lock")
+	if err != nil {
+		return err
+	}
+
 	defer func() {
-		s.must(unlock())
+		err = unlock()
+		if err != nil {
+			ret = err
+		}
 	}()
-	s.must(err)
 
 	defer func() {
 		if pArg := recover(); pArg != nil {
@@ -31,9 +43,14 @@ func main() {
 						fmt.Sprintf("An error occurred calling the registered hooks: %s", hookErr),
 					)
 				}
-				os.Exit(1)
+				ret = err
+			} else {
+				s.logger.Error(
+					fmt.Sprintf("Executing the script encountered an unrecoverable panic: %v", err),
+				)
+
+				panic(pArg)
 			}
-			panic(pArg)
 		}
 
 		if err := s.runHooks(nil); err != nil {
@@ -43,7 +60,7 @@ func main() {
 					err,
 				),
 			)
-			os.Exit(1)
+			ret = err
 		}
 		s.logger.Info("Finished running backup tasks.")
 	}()
@@ -65,4 +82,90 @@ func main() {
 	s.must(s.withLabeledCommands(lifecyclePhaseProcess, s.encryptArchive)())
 	s.must(s.withLabeledCommands(lifecyclePhaseCopy, s.copyArchive)())
 	s.must(s.withLabeledCommands(lifecyclePhasePrune, s.pruneBackups)())
+
+	return nil
+}
+
+func runInForeground() error {
+	cr := cron.New(
+		cron.WithParser(
+			cron.NewParser(
+				cron.SecondOptional | cron.Minute | cron.Hour | cron.Dom | cron.Month | cron.Dow | cron.Descriptor,
+			),
+		),
+	)
+
+	addJob := func(c *Config) error {
+		_, err := cr.AddFunc(c.BackupCronExpression, func() {
+			err := runScript(c)
+			if err != nil {
+				slog.Error("unexpected error during backup", "error", err)
+			}
+		})
+		return err
+	}
+
+	cs, err := loadEnvFiles("/etc/dockervolumebackup/conf.d")
+	if err != nil {
+		if !os.IsNotExist(err) {
+			return fmt.Errorf("could not load config from environment files, error: %w", err)
+		}
+
+		c, err := loadEnvVars()
+		if err != nil {
+			return fmt.Errorf("could not load config from environment variables")
+		} else {
+			err = addJob(c)
+			if err != nil {
+				return fmt.Errorf("could not add cron job, error: %w", err)
+			}
+		}
+	} else {
+		for _, c := range cs {
+			err = addJob(c)
+			if err != nil {
+				return fmt.Errorf("could not add cron job, error: %w", err)
+			}
+		}
+	}
+
+	var quit = make(chan os.Signal, 1)
+	signal.Notify(quit, syscall.SIGTERM, syscall.SIGINT)
+	cr.Start()
+	<-quit
+	ctx := cr.Stop()
+	<-ctx.Done()
+
+	return nil
+}
+
+func runAsCommand() error {
+	c, err := loadEnvVars()
+	if err != nil {
+		return fmt.Errorf("could not load config from environment variables, error: %w", err)
+	}
+
+	err = runScript(c)
+	if err != nil {
+		return fmt.Errorf("unexpected error during backup, error: %w", err)
+	}
+
+	return nil
+}
+
+func main() {
+	serve := flag.Bool("foreground", false, "run the tool in the foreground")
+	flag.Parse()
+
+	var err error
+	if *serve {
+		err = runInForeground()
+	} else {
+		err = runAsCommand()
+	}
+
+	if err != nil {
+		slog.Error("ran into an issue during execution", "error", err)
+		os.Exit(1)
+	}
 }

cmd/backup/script.go

@@ -30,7 +30,6 @@ import (
 	"github.com/containrrr/shoutrrr/pkg/router"
 	"github.com/docker/docker/client"
 	"github.com/leekchan/timeutil"
-	"github.com/offen/envconfig"
 	"github.com/otiai10/copy"
 	"golang.org/x/sync/errgroup"
 )
@@ -58,10 +57,10 @@ type script struct {
 // remote resources like the Docker engine or remote storage locations. All
 // reading from env vars or other configuration sources is expected to happen
 // in this method.
-func newScript() (*script, error) {
+func newScript(c *Config) (*script, error) {
 	stdOut, logBuffer := buffer(os.Stdout)
 	s := &script{
-		c:      &Config{},
+		c:      c,
 		logger: slog.New(slog.NewTextHandler(stdOut, nil)),
 		stats: &Stats{
 			StartTime: time.Now(),
@@ -83,32 +82,6 @@ func newScript() (*script, error) {
 		return nil
 	})
 
-	envconfig.Lookup = func(key string) (string, bool) {
-		value, okValue := os.LookupEnv(key)
-		location, okFile := os.LookupEnv(key + "_FILE")
-
-		switch {
-		case okValue && !okFile: // only value
-			return value, true
-		case !okValue && okFile: // only file
-			contents, err := os.ReadFile(location)
-			if err != nil {
-				s.must(fmt.Errorf("newScript: failed to read %s! Error: %s", location, err))
-				return "", false
-			}
-			return string(contents), true
-		case okValue && okFile: // both
-			s.must(fmt.Errorf("newScript: both %s and %s are set!", key, key+"_FILE"))
-			return "", false
-		default: // neither, ignore
-			return "", false
-		}
-	}
-
-	if err := envconfig.Process("", s.c); err != nil {
-		return nil, fmt.Errorf("newScript: failed to process configuration values: %w", err)
-	}
-
 	s.file = path.Join("/tmp", s.c.BackupFilename)
 
 	tmplFileName, tErr := template.New("extension").Parse(s.file)

cmd/backup/stop_restart.go

@@ -210,9 +210,9 @@ func (s *script) stopContainersAndServices() (func() error, error) {
 				warnings, err := scaleService(s.cli, svc.serviceID, 0)
 				if err != nil {
 					scaleDownErrors.append(err)
-				} else {
-					scaledDownServices = append(scaledDownServices, svc)
+					return
 				}
+				scaledDownServices = append(scaledDownServices, svc)
 				for _, warning := range warnings {
 					s.logger.Warn(
 						fmt.Sprintf("The Docker API returned a warning when scaling down service %s: %s", svc.serviceID, warning),

docs/how-tos/use-custom-docker-host.md

@@ -13,5 +13,33 @@ If you are interfacing with Docker via TCP, set `DOCKER_HOST` to the correct URL
 DOCKER_HOST=tcp://docker_socket_proxy:2375
 ```
 
-In case you are using a socket proxy, it must support `GET` and `POST` requests to the `/containers` endpoint. If you are using Docker Swarm, it must also support the `/services` endpoint. If you are using pre/post backup commands, it must also support the `/exec` endpoint.
+If you do this as you seek to restrict access to the Docker socket, this tool is potentially calling the following Docker APIs:
 
+| API | When |
+|-|-|
+| `Info` | always |
+| `ContainerExecCreate` | running commands from `exec-labels` |
+| `ContainerExecAttach` | running commands from `exec-labels` |
+| `ContainerExecInspect` | running commands from `exec-labels` |
+| `ContainerList` | always |
+  `ServiceList` | Docker engine is running in Swarm mode |
+| `ServiceInspect` | Docker engine is running in Swarm mode |
+| `ServiceUpdate` | Docker engine is running in Swarm mode and `stop-during-backup` is used |
+| `ConatinerStop` | `stop-during-backup` labels are applied to containers |
+| `ContainerStart` | `stop-during-backup` labels are applied to container |
+
+---
+
+In case you are using [`docker-socket-proxy`][proxy], this means following permissions are required:
+
+| Permission | When |
+|-|-|
+| INFO | always required |
+| CONTAINERS | always required |
+| POST | required when using `stop-during-backup` or `exec` labels |
+| EXEC | required when using `exec`-labeled commands |
+| SERVICES | required when Docker Engine is running in Swarm mode |
+| NODES | required when labeling services `stop-during-backup` |
+| TASKS | required when labeling services `stop-during-backup` |
+
+[proxy]: https://github.com/Tecnativa/docker-socket-proxy

docs/reference/index.md

@@ -23,9 +23,22 @@ You can populate below template according to your requirements and use it as you
 ```
 ########### BACKUP SCHEDULE
 
-# Backups run on the given cron schedule in `busybox` flavor. If no
-# value is set, `@daily` will be used. If you do not want the cron
-# to ever run, use `0 0 5 31 2 ?`.
+
+# A cron expression represents a set of times, using 5 or 6 space-separated fields.
+#
+# Field name   | Mandatory? | Allowed values  | Allowed special characters
+# ----------   | ---------- | --------------  | --------------------------
+# Seconds      | No         | 0-59            | * / , -
+# Minutes      | Yes        | 0-59            | * / , -
+# Hours        | Yes        | 0-23            | * / , -
+# Day of month | Yes        | 1-31            | * / , - ?
+# Month        | Yes        | 1-12 or JAN-DEC | * / , -
+# Day of week  | Yes        | 0-6 or SUN-SAT  | * / , - ?
+#
+# Month and Day-of-week field values are case insensitive.
+# "SUN", "Sun", and "sun" are equally accepted.
+# If no value is set, `@daily` will be used.
+# If you do not want the cron to ever run, use `0 0 5 31 2 ?`.
 
 # BACKUP_CRON_EXPRESSION="0 2 * * *"
 

go.mod

@@ -10,7 +10,7 @@ require (
 	github.com/docker/cli v24.0.1+incompatible
 	github.com/docker/docker v24.0.7+incompatible
 	github.com/gofrs/flock v0.8.1
-	github.com/klauspost/compress v1.17.5
+	github.com/klauspost/compress v1.17.6
 	github.com/leekchan/timeutil v0.0.0-20150802142658-28917288c48d
 	github.com/minio/minio-go/v7 v7.0.66
 	github.com/offen/envconfig v1.5.0
@@ -28,6 +28,8 @@ require (
 	github.com/golang-jwt/jwt/v5 v5.2.0 // indirect
 	github.com/golang/protobuf v1.5.3 // indirect
 	golang.org/x/time v0.0.0-20220609170525-579cf78fd858 // indirect
+	github.com/joho/godotenv v1.5.1 // indirect
+	github.com/robfig/cron/v3 v3.0.0 // indirect
 	google.golang.org/appengine v1.6.7 // indirect
 	google.golang.org/protobuf v1.31.0 // indirect
 )

go.sum

@@ -443,6 +443,8 @@ github.com/ianlancetaylor/demangle v0.0.0-20200824232613-28f6c0f3b639/go.mod h1:
 github.com/inconshreveable/mousetrap v1.0.1/go.mod h1:vpF70FUmC8bwa3OWnCshd2FqLfsEA9PFc4w1p2J65bw=
 github.com/jarcoal/httpmock v1.2.0 h1:gSvTxxFR/MEMfsGrvRbdfpRUMBStovlSRLw0Ep1bwwc=
 github.com/jarcoal/httpmock v1.2.0/go.mod h1:oCoTsnAz4+UoOUIf5lJOWV2QQIW5UoeUI6aM2YnWAZk=
+github.com/joho/godotenv v1.5.1 h1:7eLL/+HRGLY0ldzfGMeQkb7vMd0as4CfYvUVzLqw0N0=
+github.com/joho/godotenv v1.5.1/go.mod h1:f4LDr5Voq0i2e/R5DDNOoa2zzDfwtkZa6DnEwAbqwq4=
 github.com/jpillora/backoff v1.0.0/go.mod h1:J/6gKK9jxlEcS3zixgDgUAsiuZ7yrSoa/FX5e0EB2j4=
 github.com/json-iterator/go v1.1.6/go.mod h1:+SdeFBvtyEkXs7REEP0seUULqWtbJapLOCVDaaPEHmU=
 github.com/json-iterator/go v1.1.9/go.mod h1:KdQUCv79m/52Kvf8AW2vK1V8akMuk1QjK/uOdHXbAo4=
@@ -456,8 +458,8 @@ github.com/julienschmidt/httprouter v1.2.0/go.mod h1:SYymIcj16QtmaHHD7aYtjjsJG7V
 github.com/julienschmidt/httprouter v1.3.0/go.mod h1:JR6WtHb+2LUe8TCKY3cZOxFyyO8IZAc4RVcycCCAKdM=
 github.com/kisielk/errcheck v1.5.0/go.mod h1:pFxgyoBC7bSaBwPgfKdkLd5X25qrDl4LWUI2bnpBCr8=
 github.com/kisielk/gotool v1.0.0/go.mod h1:XhKaO+MFFWcvkIS/tQcRk01m1F5IRFswLeQ+oQHNcck=
-github.com/klauspost/compress v1.17.5 h1:d4vBd+7CHydUqpFBgUEKkSdtSugf9YFmSkvUYPquI5E=
-github.com/klauspost/compress v1.17.5/go.mod h1:/dCuZOvVtNoHsyb+cuJD3itjs3NbnF6KH9zAO4BDxPM=
+github.com/klauspost/compress v1.17.6 h1:60eq2E/jlfwQXtvZEeBUYADs+BwKBWURIY+Gj2eRGjI=
+github.com/klauspost/compress v1.17.6/go.mod h1:/dCuZOvVtNoHsyb+cuJD3itjs3NbnF6KH9zAO4BDxPM=
 github.com/klauspost/cpuid/v2 v2.0.1/go.mod h1:FInQzS24/EEf25PyTYn52gqo7WaD8xa0213Md/qVLRg=
 github.com/klauspost/cpuid/v2 v2.2.6 h1:ndNyv040zDGIDh8thGkXYjnFtiN02M1PVVF+JE/48xc=
 github.com/klauspost/cpuid/v2 v2.2.6/go.mod h1:Lcz8mBdAVJIBVzewtcLocK12l3Y+JytZYpaMropDUws=
@@ -593,6 +595,8 @@ github.com/prometheus/procfs v0.0.2/go.mod h1:TjEm7ze935MbeOT/UhFTIMYKhuLP4wbCsT
 github.com/prometheus/procfs v0.0.8/go.mod h1:7Qr8sr6344vo1JqZ6HhLceV9o3AJ1Ff+GxbHq6oeK9A=
 github.com/prometheus/procfs v0.1.3/go.mod h1:lV6e/gmhEcM9IjHGsFOCxxuZ+z1YqCvr4OA4YeYWdaU=
 github.com/prometheus/procfs v0.6.0/go.mod h1:cz+aTbrPOrUb4q7XlbU9ygM+/jj0fzG6c1xBZuNvfVA=
+github.com/robfig/cron/v3 v3.0.0 h1:kQ6Cb7aHOHTSzNVNEhmp8EcWKLb4CbiMW9h9VyIhO4E=
+github.com/robfig/cron/v3 v3.0.0/go.mod h1:eQICP3HwyT7UooqI/z+Ov+PtYAWygg1TEWWzGIFLtro=
 github.com/rogpeppe/fastuuid v1.2.0/go.mod h1:jVj6XXZzXRy/MSR5jhDC/2q6DgLz+nrA6LYCDYWNEvQ=
 github.com/rogpeppe/go-internal v1.3.0/go.mod h1:M8bDsm7K2OlrFYOpmOWEs/qY81heoFRclV5y23lUDJ4=
 github.com/rogpeppe/go-internal v1.6.1/go.mod h1:xXDCJY+GAPziupqXw64V24skbSoqbTEfhy4qGm1nDQc=

test/lock/docker-compose.yml

@@ -0,0 +1,23 @@
+version: '3'
+
+services:
+  backup:
+    image: offen/docker-volume-backup:${TEST_VERSION:-canary}
+    restart: always
+    environment:
+      BACKUP_CRON_EXPRESSION: 0 0 5 31 2 ?
+      BACKUP_RETENTION_DAYS: '7'
+    volumes:
+      - app_data:/backup/app_data:ro
+      - /var/run/docker.sock:/var/run/docker.sock
+      - ${LOCAL_DIR:-./local}:/archive
+
+  offen:
+    image: offen/offen:latest
+    labels:
+      - docker-volume-backup.stop-during-backup=true
+    volumes:
+      - app_data:/var/opt/offen
+
+volumes:
+  app_data:

test/lock/run.sh

@@ -0,0 +1,34 @@
+#!/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
+
+ec=0
+
+docker compose exec -e BACKUP_RETENTION_DAYS=7 -e BACKUP_FILENAME=test.tar.gz backup backup & \
+  { set +e; sleep 0.1; docker compose exec -e BACKUP_FILENAME=test2.tar.gz -e LOCK_TIMEOUT=1s backup backup; ec=$?;}
+
+if [ "$ec" = "0" ]; then
+  fail "Subsequent invocation exited 0"
+fi
+pass "Subsequent invocation did not exit 0"
+
+sleep 5
+
+if [ ! -f "${LOCAL_DIR}/test.tar.gz" ]; then
+  fail "Could not find expected tar file"
+fi
+pass "Found expected tar file"
+
+if [ -f "${LOCAL_DIR}/test2.tar.gz" ]; then
+  fail "Subsequent invocation was expected to fail but created archive"
+fi
+pass "Subsequent invocation did not create archive"

test/proxy/docker-compose.swarm.yml

@@ -0,0 +1,40 @@
+# Copyright 2020-2021 - Offen Authors <hioffen@posteo.de>
+# SPDX-License-Identifier: Unlicense
+
+version: '3.8'
+
+services:
+  backup:
+    image: offen/docker-volume-backup:${TEST_VERSION:-canary}
+    environment:
+      BACKUP_FILENAME: test.tar.gz
+      BACKUP_CRON_EXPRESSION: 0 0 5 31 2 ?
+      DOCKER_HOST: tcp://docker_socket_proxy:2375
+    volumes:
+      - pg_data:/backup/pg_data:ro
+      - ${LOCAL_DIR:-local}:/archive
+
+  docker_socket_proxy:
+    image: tecnativa/docker-socket-proxy:0.1
+    environment:
+      INFO: ${ALLOW_INFO:-1}
+      CONTAINERS: ${ALLOW_CONTAINERS:-1}
+      SERVICES: ${ALLOW_SERVICES:-1}
+      POST: ${ALLOW_POST:-1}
+      TASKS: ${ALLOW_TASKS:-1}
+      NODES: ${ALLOW_NODES:-1}
+    volumes:
+      - /var/run/docker.sock:/var/run/docker.sock
+
+  pg:
+    image: postgres:14-alpine
+    environment:
+      POSTGRES_PASSWORD: example
+    volumes:
+      - pg_data:/var/lib/postgresql/data
+    deploy:
+      labels:
+        - docker-volume-backup.stop-during-backup=true
+
+volumes:
+  pg_data:

test/proxy/docker-compose.yml

@@ -0,0 +1,36 @@
+# Copyright 2020-2021 - Offen Authors <hioffen@posteo.de>
+# SPDX-License-Identifier: Unlicense
+
+version: '3.8'
+
+services:
+  backup:
+    image: offen/docker-volume-backup:${TEST_VERSION:-canary}
+    environment:
+      BACKUP_FILENAME: test.tar.gz
+      BACKUP_CRON_EXPRESSION: 0 0 5 31 2 ?
+      DOCKER_HOST: tcp://docker_socket_proxy:2375
+    volumes:
+      - pg_data:/backup/pg_data:ro
+      - ${LOCAL_DIR:-local}:/archive
+
+  docker_socket_proxy:
+    image: tecnativa/docker-socket-proxy:0.1
+    environment:
+      INFO: ${ALLOW_INFO:-1}
+      CONTAINERS: ${ALLOW_CONTAINERS:-1}
+      POST: ${ALLOW_POST:-1}
+    volumes:
+      - /var/run/docker.sock:/var/run/docker.sock
+
+  pg:
+    image: postgres:14-alpine
+    environment:
+      POSTGRES_PASSWORD: example
+    volumes:
+      - pg_data:/var/lib/postgresql/data
+    labels:
+      - docker-volume-backup.stop-during-backup=true
+
+volumes:
+  pg_data:

test/proxy/run.sh

@@ -0,0 +1,76 @@
+#!/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
+
+# The default configuration in docker-compose.yml should
+# successfully create a backup.
+docker compose exec backup backup
+
+sleep 5
+
+expect_running_containers "3"
+
+if [ ! -f "$LOCAL_DIR/test.tar.gz" ]; then
+  fail "Archive was not created"
+fi
+pass "Found relevant archive file."
+
+# Disabling POST should make the backup run fail
+ALLOW_POST="0" docker compose up -d
+sleep 5
+
+set +e
+docker compose exec backup backup
+if [ $? = "0" ]; then
+  fail "Expected invocation to exit non-zero."
+fi
+set -e
+pass "Invocation exited non-zero."
+
+docker compose down --volumes
+
+# Next, the test is run against a Swarm setup
+
+docker swarm init
+
+export LOCAL_DIR=$(mktemp -d)
+
+docker stack deploy --compose-file=docker-compose.swarm.yml test_stack
+
+sleep 20
+
+# The default configuration in docker-compose.swarm.yml should
+# successfully create a backup in Swarm mode.
+docker exec $(docker ps -q -f name=backup) backup
+
+if [ ! -f "$LOCAL_DIR/test.tar.gz" ]; then
+  fail "Archive was not created"
+fi
+
+pass "Found relevant archive file."
+
+sleep 5
+expect_running_containers "3"
+
+# Disabling POST should make the backup run fail
+ALLOW_POST="0" docker stack deploy --compose-file=docker-compose.swarm.yml test_stack
+
+sleep 20
+
+set +e
+docker exec $(docker ps -q -f name=backup) backup
+if [ $? = "0" ]; then
+  fail "Expected invocation to exit non-zero."
+fi
+set -e
+
+pass "Invocation exited non-zero."