copy-squid-docker-volume

#!/bin/bash
# copy-squid-volume.sh - copy any [anonymous] Docker volumes with squid caches to a new volume
# 
# Set environment variable FORCE_CREATE_VOLUME=1 to skip confirmation check when a volume exists

set -e
[ -n "${DEBUG:-}" ] && set -x # set DEBUG=1 to enable tracing

if [ ! `id -u` = "0" ] ; then
    echo "$0: Error: you must be root to view docker volumes" 1>&2
    exit 1
fi

_usage () {
    cat <<EOUSAGE
Usage: $0 [OPTIONS] NEW_VOLUME

Options:
  -h,--help                 This screen
  -f,--force                Skip confirmation when new volume exists

This script finds any Docker volumes which look like Squid caches, and copies them
into a new Docker volume called NEW_VOLUME.
EOUSAGE
    exit 1
}

_create_vol () {
    local name="$1"
    local newvolid="$(docker volume ls --filter name="$name" -q)"
    if [ -n "$newvolid" ] ; then
        echo "$0: Warning: volume '$name' already exists ($newvolid)" 1>&2
        if [ "${FORCE_CREATE_VOLUME:-0}" = "1" ] ; then
            return
        fi
        read -p "Continue anyway? [y/N] " ANSWER
        if [ ! "$ANSWER" = "y" -a ! "$ANSWER" = "Y" ] ; then
            echo "$0: Bailing out" 1>&2
            exit 1
        fi
    else
        docker volume create --label name="$name" --label type="squidcache" "$name"
    fi
}

_find_squid_vol () {
    local newvolname="$1"
    local volids=""
    local newvolid="$(docker volume ls --filter name="$newvolname" -q)"
    echo "$0: Info: Looking for Docker volumes with Squid caches..." 1>&2
    while read -r dvolid ; do
        mpoint=$(docker inspect "$dvolid" --format "{{.Mountpoint}}")
        # squid keeps a 'swap.state' for its default cache storage method
        if [ -e "$mpoint/swap.state" ] ; then 
            # Skip the 'new' volume if it already existed
            [ "$dvolid" = "$newvolid" ] && continue 
            volids="$(printf "%s\t%s" "$volids" "$dvolid")"
        fi
    done < <(docker volume ls -q) # read from a pipe in a while loop in current shell session
    printf "$volids\n"
}

_copy_vol () {
    local oldvol="$1"
    local newvol="$2"
    # I don't know a simpler/less resource-inefficient way to do this :(
    # Requires downloading Busybox container, ~750KB
    echo "$0: Copying Docker volume '$oldvol' into '$newvol' ..." 1>&2
    docker run --rm -v "$oldvol:/oldvol" -v "$newvol:/newvol" busybox sh -c "cd /newvol && cp -a /oldvol/* ."
}

_copy_squid_vols () {
    local newvolname="$1"
    local squid_vol_ids="$(_find_squid_vol "$newvolname")"
    if [ -n "$squid_vol_ids" ] ; then
        _create_vol "$newvolname"

        for volid in $squid_vol_ids ; do
            _copy_vol "$volid" "$newvolname"
        done
    else
        echo "$0: Error: could not find any squid volumes to copy" 1>&2
        exit 1
    fi
}

[ $# -lt 1 -o "$1" = "-h" -o "$1" = "--help" ] && _usage

if [ "$1" = "-f" -o "$1" = "--force" ] ; then
    FORCE_CREATE_VOLUME=1
    shift
fi

NEWVOLNAME="$1"
_copy_squid_vols "$NEWVOLNAME"
exit $?