Backup PostgreSQL database running in a container on Digital Ocean

Question

I'm a newbie to Docker, I'm working on a project that written by another developer, the project is running on Digital Ocean Ubuntu 18.04. It consists of 2 containers (1 container for Django App, 1 container for PostgreSQL database).

It is required from me now to get a backup of database, I found a bash file written by previous programmer:

### Create a database backup.
###
### Usage:
###     $ docker-compose -f <environment>.yml (exec |run --rm) postgres backup
set -o errexit
set -o pipefail
set -o nounset


working_dir="$(dirname ${0})"
source "${working_dir}/_sourced/constants.sh"
source "${working_dir}/_sourced/messages.sh"


message_welcome "Backing up the '${POSTGRES_DB}' database..."


if [[ "${POSTGRES_USER}" == "postgres" ]]; then
    message_error "Backing up as 'postgres' user is not supported. Assign 'POSTGRES_USER' env with another one and try again."
    exit 1
fi

export PGHOST="${POSTGRES_HOST}"
export PGPORT="${POSTGRES_PORT}"
export PGUSER="${POSTGRES_USER}"
export PGPASSWORD="${POSTGRES_PASSWORD}"
export PGDATABASE="${POSTGRES_DB}"

backup_filename="${BACKUP_FILE_PREFIX}_$(date +'%Y_%m_%dT%H_%M_%S').sql.gz"
pg_dump | gzip > "${BACKUP_DIR_PATH}/${backup_filename}"


message_success "'${POSTGRES_DB}' database backup '${backup_filename}' has been created and placed in '${BACKUP_DIR_PATH}'."

my first question is:
is that command right? i mean if i ran:

docker-compose -f production.yml (exec |run --rm) postgres backup

Would that create a backup for my database at the written location?

Second question: can I run this command while the database container is running? or should I run docker-compose down then run the command for backup then run docker-compose up again.

run runs a cmd in a new container, exec runs a cmd in an existing container. You don't need to run docker-compose down. — snahor
– snahor, Commented Sep 11, 2020 at 4:09
@snahor what about the command? would be right that way? I mean (exec |run --rm) is that right? — Ahmed Munir
– Ahmed Munir, Commented Sep 11, 2020 at 4:56
@snahor I got it, he meant by his command that if the container is running I will use exec, but if the container is down I will use run --rm which will create a new container for DB, and after making the backup it will take it down. Thx very much man — Ahmed Munir
– Ahmed Munir, Commented Sep 11, 2020 at 5:32

MaxJRB · Accepted Answer · 2020-09-11 06:09:03Z

Sure you can run that script to backup, one way to do it is executing a shell in container with docker-compose exec db /bin/bash and then run that script.

Other way is running a new postgres container attached to the postgres container network:

docker run -it --name pgback -v /path/backup/host:/var/lib/postgresql/data --network composeNetwork postgres /bin/bash

this will create a new postgres container attached to the network created with compose, with a binding volume attached, then you can create this script in the container and back up the database to the volume to save it to other place out of container.

Then when you want to backup simple start docker container and backup: docker start -a -i pgback

You dont need to create other compose file, just copy the script to he container and run it, also you could create a new postgres image with the script and run it from CMD, just to run the container, there are plenty ways to do it.

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