Clone a PostgreSQL server using Docker and Union Mounting

pgclone.sh

#!/bin/bash

# This simple script mounts a PostgreSQL data directory as
# the lower dir, and a temp directory as the upper dir of
# a union mount; then bind mounts the volume into a docker
# container, running a new instance of PostgreSQL/PostGIS.
#
# This enables the user to run tests and migrations on
# production data, without worrying about data integrity or
# using too much storage for a full clone.
#
# It can also be replaced with this Volume Plugin which
# basically does the same thing:
# https://github.com/Fardinak/docker-volume-unionmount

CONTAINER_NAME=$2
CONTAINER_TARGET_DIR=/var/lib/postgresql/data
TEMP_DIR=/tmp/${CONTAINER_NAME}_pgdata
DATA_DIR=${3:/var/lib/postgresql/data}
IMAGE=${4:"postgres:latest"}

if [[ ! -e /root ]]; then
	echo "error: data directory (${DATA_DIR}) does not exist!"
	exit 1
fi;

if [[ $1 == "start" && $2 ]]; then
	mkdir -p $TEMP_DIR
	umount -f $TEMP_DIR
	# mount -t overlay overlay -o lowerdir=$DATA_DIR,upperdir=$TEMP_DIR $TEMP_DIR
	mount -t aufs -o br:$TEMP_DIR:$DATA_DIR none $TEMP_DIR
	docker run --name $CONTAINER_NAME -d -v $TEMP_DIR:$CONTAINER_TARGET_DIR:ro $IMAGE
elif [[ $1 == "stop" && $2 ]]; then
	docker stop $CONTAINER_NAME
	docker rm -v $CONTAINER_NAME
	umount $TEMP_DIR
else
	echo -e "pgclone is a tool for creating a sandbox clone of a PostgreSQL database"
	echo -e "using docker and the overlay filesystem."
	echo -e ""
	echo -e "Usage: $0 command container_name [data_dir [image]]"
	echo -e ""
	echo -e "Commands:"
	echo -e "\tstart\tStarts a new container by given name"
	echo -e "\tstop\tStops the given container and removes it (and it's volumes)"
	echo -e ""
	echo -e "Defaults:"
	echo -e "\tdata_dir\t/var/lib/postgresql/data"
	echo -e "\timage\t\tpostgres:latest"
fi;