Obtain locks before restoring or backing up

Dockerfile.raspbian

@@ -28,13 +28,15 @@ RUN apt-get update \
 
 RUN [ "cross-build-end" ]
 
-VOLUME "/root/.cache/duplicity"
-VOLUME "/backups"
+VOLUME /root/.cache/duplicity
+VOLUME /backups
+VOLUME /var/lock/duplicity
 
 ENV BACKUP_DEST="file:///backups"
 ENV BACKUP_NAME="backup"
 ENV PATH_TO_BACKUP="/data"
 ENV PASSPHRASE="Correct.Horse.Battery.Staple"
+ENV FLOCK_WAIT=60
 
 # Cron schedules
 ENV CRON_SCHEDULE=""

Dockerfile.ubuntu

@@ -28,13 +28,15 @@ RUN apt-get update \
         && apt-get clean \
         && rm -rf /var/apt/lists/*
 
-VOLUME "/root/.cache/duplicity"
-VOLUME "/backups"
+VOLUME /root/.cache/duplicity
+VOLUME /backups
+VOLUME /var/lock/duplicity
 
 ENV BACKUP_DEST="file:///backups"
 ENV BACKUP_NAME="backup"
 ENV PATH_TO_BACKUP="/data"
 ENV PASSPHRASE="Correct.Horse.Battery.Staple"
+ENV FLOCK_WAIT=60
 
 # Cron schedules
 ENV CRON_SCHEDULE=""

Readme.md

@@ -15,6 +15,7 @@ Mount any directories you'd like to back up as a volume and run
 |BACKUP_NAME|backup|What the name for the backup should be. If using a single store for multiple backups, make sure this is unique|
 |CLEANUP_COMMAND| |An optional duplicity command to execute after backups to clean older ones out (eg. "remove-all-but-n-full 2")|
 |CRON_SCHEDULE| |If you want to periodic incremental backups on a schedule, provide it here. By default we just backup once and exit|
+|FLOCK_WAIT|60|Seconds to wait for a lock before skipping a backup|
 |FTP_PASSWORD| |Used to provide passwords for some backends. May not work without an attached TTY|
 |FULL_CRON_SCHEDULE| |If you want to periodic full backups on a schedule, provide it here. This requires an incremental cron schedule too.|
 |GPG_KEY_ID| |The ID of the key you wish to use. See [Encryption](#encryption) section below|

backup.sh

@@ -1,7 +1,13 @@
 #! /bin/bash
 set -e
 
-duplicity \
+(
+    if ! flock -x -w $FLOCK_WAIT 200 ; then
+        echo 'ERROR: Could not obtain lock. Exiting.'
+        exit 1
+    fi
+
+    duplicity \
         $1 \
         --asynchronous-upload \
         --log-file /root/duplicity.log \
@@ -10,9 +16,10 @@ duplicity \
         $PATH_TO_BACKUP \
         $BACKUP_DEST
 
-if [ -n "$CLEANUP_COMMAND" ]; then
+    if [ -n "$CLEANUP_COMMAND" ]; then
         duplicity $CLEANUP_COMMAND \
             --log-file /root/duplicity.log \
             --name $BACKUP_NAME \
             $BACKUP_DEST
-fi
+    fi
+) 200>/var/lock/duplicity/.duplicity.lock

restore.sh

@@ -1,7 +1,13 @@
 #! /bin/bash
 set -e
 
-duplicity restore \
+(
+    if ! flock -x -w $FLOCK_WAIT 200 ; then
+        echo 'ERROR: Could not obtain lock. Exiting.'
+        exit 1
+    fi
+
+    duplicity restore \
         --force \
         --log-file /root/duplicity.log \
         --name $BACKUP_NAME \
@@ -9,3 +15,4 @@ duplicity restore \
         $@ \
         $BACKUP_DEST \
         $PATH_TO_BACKUP
+) 200>/var/lock/duplicity/.duplicity.lock