Rename example.env to .env and set the environment variables.

FTP_HOST=ftp.example.com
FTP_USER=user
FTP_PASS=password
FTP_SOURCE=/
FTP_TARGET=/sync

To use LFTP over SSH:

FTP_HOST=sftp://ftp.example.com

Update crontab to set the required frequency. The default value runs the sync every hour. Check the https://crontab.guru to explore more options.

0 * * * * /bin/sh /mirror.sh > /proc/1/fd/1 2>/proc/1/fd/2

Run as a service

docker-compose build

docker-compose up -d

Run sync manually

FTP_HOST=ftp.example.com FTP_USER=user FTP_PASS=password FTP_SOURCE=/ FTP_TARGET=./sync ./mirror.sh

Test

lftp -e "
set ssl:verify-certificate no;
set sftp:auto-confirm yes;
open sftp://ftp.example.com;
user user password;
ls -l;
bye;
"

Check the https://lftp.yar.ru/lftp-man.html to explore more options.