Document socket-proxy permissions, return early when update failed on scaling down (#343)

* Do not await containers when there was an error on scaling

* Add test case for usage with socket proxy

* Add documentation on required permissions for docker-socket-proxy

* Add full list of used Docker APIs to doc

* CONTAINER_START and CONTAINER_STOP is not needed

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."