docker-volume-backup

Backup Docker volumes locally or to any S3 compatible storage.

The offen/docker-volume-backup Docker image can be used as a sidecar container to an existing Docker setup. It handles recurring backups of Docker volumes to a local directory or any S3 compatible storage (or both) and rotates away old backups if configured.

Configuration

Backup targets, schedule and retention are configured in environment variables:

########### BACKUP SCHEDULE

# Backups run on the given cron schedule and use the filename defined in the
# template expression.

BACKUP_CRON_EXPRESSION="0 2 * * *"
# Format verbs will be replaced as in the `date` command. Omitting them
# will result in the same filename for every backup run, which means previous
# versions will be overwritten.
BACKUP_FILENAME="backup-%Y-%m-%dT%H-%M-%S.tar.gz"

########### BACKUP STORAGE

# Define credentials for authenticating against the backup storage and a bucket
# name. Although all of these values are `AWS`-prefixed, the setup can be used
# with any S3 compatible storage.

AWS_ACCESS_KEY_ID="<xxx>"
AWS_SECRET_ACCESS_KEY="<xxx>"
AWS_S3_BUCKET_NAME="<xxx>"

# This is the FQDN of your storage server, e.g. `storage.example.com`.
# Do not set this when working against AWS S3. If you need to set a
# specific protocol, you will need to use the option below.

# AWS_ENDPOINT="<xxx>"

# The protocol to be used when communicating with your storage server.
# Defaults to "https". You can set this to "http" when communicating with
# a different Docker container on the same host for example.

# AWS_ENDPOINT_PROTO="https"

# Setting this variable to any value will disable verification of
# SSL certificates. You shouldn't use this unless you use self-signed
# certificates for your remote storage backend.

# AWS_ENDPOINT_INSECURE="true"

# In addition to backing up you can also store backups locally. Pass in
# a local path to store your backups here if needed. You likely want to
# mount a local folder or Docker volume into that location when running
# the container. Local paths can also be subject to pruning of old
# backups as defined below.

# BACKUP_ARCHIVE="/archive"

########### BACKUP PRUNING

# **IMPORTANT, PLEASE READ THIS BEFORE USING THIS FEATURE**:
# The mechanism used for pruning backups is not very sophisticated
# and applies its rules to **all files in the target directory** by default,
# which means that if you are storing your backups next to other files,
# these might become subject to deletion too. When using this option
# make sure the backup files are stored in a directory used exclusively
# for storing them or to configure BACKUP_PRUNING_PREFIX to limit
# removal to certain files.

# Define this value to enable automatic pruning of old backups. The value
# declares the number of days for which a backup is kept.

# BACKUP_RETENTION_DAYS="7"

# In case the duration a backup takes fluctuates noticeably in your setup
# you can adjust this setting to make sure there are no race conditions
# between the backup finishing and the rotation not deleting backups that
# sit on the very edge of the time window. Set this value to a duration
# that is expected to be bigger than the maximum difference of backups.
# Valid values have a suffix of (s)econds, (m)inutes or (h)ours.

# BACKUP_PRUNING_LEEWAY="1m"

# In case your target bucket or directory contains other files than the ones
# managed by this container, you can limit the scope of rotation by setting
# a prefix value. This would usually be the non-parametrized part of your
# BACKUP_FILENAME. E.g. if BACKUP_FILENAME is `db-backup-%Y-%m-%dT%H-%M-%S.tar.gz`,
# you can set BACKUP_PRUNING_PREFIX to `db-backup-` and make sure
# unrelated files are not affected.

# BACKUP_PRUNING_PREFIX="backup-"

########### BACKUP ENCRYPTION

# Backups can be encrypted using gpg in case a passphrase is given

# GPG_PASSPHRASE="<xxx>"

########### STOPPING CONTAINERS DURING BACKUP

# Containers can be stopped by applying a
# `docker-volume-backup.stop-during-backup` label. By default, all containers
# that are labeled with `true` will be stopped. If you need more fine grained
# control (e.g. when running multiple containers based on this image), you can
# override this default by specifying a different value here.

# BACKUP_STOP_CONTAINER_LABEL="service1"

Example in a docker-compose setup

Most likely, you will use this image as a sidecar container in an existing docker-compose setup like this:

version: '3'

services:
  volume-consumer:
    build:
      context: ./my-app
    volumes:
      - data:/var/my-app
    labels:
      # This means the container will be stopped during backup to ensure
      # backup integrity. You can omit this label if stopping during backup
      # not required.
      - docker-volume-backup.stop-during-backup=true

  backup:
    image: offen/docker-volume-backup:latest
    restart: always
    env_file: ./backup.env
    volumes:
      # Mounting the Docker socket allows the script to stop and restart
      # the container during backup. You can omit this if you don't want
      # to stop the container
      - /var/run/docker.sock:/var/run/docker.sock:ro
      - data:/backup/my-app-backup:ro
      # If you mount a local directory or volume to `/archive` a local
      # copy of the backup will be stored there. You can override the
      # location inside of the container by setting `BACKUP_ARCHIVE`
      # - /path/to/local_backups:/archive
volumes:
  data:

Using with Docker Swarm

By default, Docker Swarm will restart stopped containers automatically, even when manually stopped. If you plan to have your containers / services stopped during backup, this means you need to apply the on-failure restart policy to your service's definitions. A restart policy of always is not compatible with this tool.

---

When running in Swarm mode, it's also advised to set a hard memory limit on your service (~25MB should be enough in most cases, but if you backup large files above half a gigabyte or similar, you might have to raise this in case the backup exits with Killed):

services:
  backup:
    image: offen/docker-volume-backup:latest
    deployment:
      resources:
        limits:
          memory: 25M

Manually triggering a backup

You can manually trigger a backup run outside of the defined cron schedule by executing the backup command inside the container:

docker exec <container_ref> backup

---

Differences to futurice/docker-volume-backup

This image is heavily inspired by the futurice/docker-volume-backup. We decided to publish this image as a simpler and more lightweight alternative because of the following requirements:

• The original image is based on ubuntu and additional tools, making it very heavy. This version is roughly 1/25 in compressed size (it's ~12MB).
• The original image uses a shell script, when this is written in Go.
• The original image proposed to handle backup rotation through AWS S3 lifecycle policies. This image adds the option to rotate away old backups through the same command so this functionality can also be offered for non-AWS storage backends like MinIO. Local copies of backups can also be pruned once they reach a certain age.
• InfluxDB specific functionality was removed.
• arm64 and arm/v7 architectures are supported.
• Docker in Swarm mode is supported.