Improve Swarm support (#333)

* Query for labeled services as well

* Try scaling down services

* Scale services back up

* Use progress tool from Docker CLI

* In test, label both services

* Clean up error and log messages

* Document scale-up/down approach in docs

* Downgrade Docker CLI to match client

* Document services stats

* Do not rely on PreviousSpec for storing desired replica count

* Log warnings from Docker when updating services

* Check whether container and service labels collide

* Document script behavior on label collision

* Add additional check if all containers have been removed

* Scale services concurrently

* Move docker interaction code into own file

* Factor out code for service updating

* Time out after five minutes of not reaching desired container count

* Inline handling of in-swarm container level restart

* Timer is more suitable for timeout race

* Timeout when scaling down services should be configurable

* Choose better filename

* Reflect changes in naming

* Rename and deprecate BACKUP_STOP_CONTAINER_LABEL

* Improve logging

* Further simplify logging

test/collision/docker-compose.yml

@@ -0,0 +1,28 @@
+# 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
+    volumes:
+      - offen_data:/backup/offen_data:ro
+      - ${LOCAL_DIR:-./local}:/archive
+      - /var/run/docker.sock:/var/run/docker.sock
+
+  offen:
+    image: offen/offen:latest
+    labels:
+      - docker-volume-backup.stop-during-backup=true
+    deploy:
+      labels:
+        - docker-volume-backup.stop-during-backup=true
+      replicas: 2
+    volumes:
+      - offen_data:/var/opt/offen
+
+volumes:
+  offen_data: