Offline Backup: RSYNC to ServerA from ServerB

Summary
Do offline backup from copying backup medias to another Server


How-to
1. On ServerA

# useradd BACKUP-SRV
# passwd BACKUP-SRV

2. On ServerB

# Private Key: ~/.ssh/id_rsa
# Public Key: ~/.ssh/id_rsa.pub
#
#@ref https://en.wikipedia.org/wiki/Key_size#Asymmetric_algorithm_key_lengths
# ssh-keygen -b 4096 -t rsa

Generating public/private rsa key pair.
Enter file in which to save the key (/home/APP-SRV/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/APP-SRV/.ssh/id_rsa.
Your public key has been saved in /home/APP-SRV/.ssh/id_rsa.pub.
The key fingerprint is: {KEY}
The key's randomart image is:
+--[ RSA 4096]----+
|                 |
|   [.........]   |
|                 |
+-----------------+

Copy the public key to ServerA

# scp ~/.ssh/id_rsa.pub BACKUP-SRV@ServerA:

OR

# scp ~/.ssh/id_rsa.pub BACKUP-SRV@ServerA:~/.ssh/authorized_keys

3. On ServerA
Create ~/.ssh/authorized_keys if not have

# touch ~/.ssh/authorized_keys

# cat ~/id_rsa.pub >> ~/.ssh/authorized_keys
# rm ~/id_rsa.pub

chmod 700 ~/.ssh
chmod 600 ~/.ssh/authorized_keys

Edit /etc/ssh/sshd_config

PubkeyAuthentication yes
AuthorizedKeysFile .ssh/authorized_keys
AllowUsers BACKUP-SRV@ServerB

4. On ServerB
# 7am Daily
/etc/crontab:

0 7 * * * UserA rsync -avz -e "ssh -p22" --del /home/APP-SRV/backup/ BACKUP-SRV@ServerA:/store/APP-SRV-Backup/ > /dev/null 2>&1

Update