Guides and examples

Role design goals

Host backups performed by the rsnapshot script are a very efficient method to keep time-based snapshots of local or remote systems. Unfortunately, the default method of creating backups using one configuration file and backing up remote hosts in order is inconvenient: all hosts managed through this single file will be backed up each time, there's only one set of snapshots that can be used this way, and any error will stop backups of hosts further along the config file.

To avoid this issue, the debops.rsnapshot role uses combination of batch(1), cron(8) and custom scheduler script written in Bash to perform backups of multiple remote hosts at the same time, each one configured in its own rsnapshot.conf configuration file, with its own lists of snapshots to manage, its own include/exclude lists, and so on.

How rsnapshot backups are performed

The whole backup sequence is:

  1. cron launches rsnapshot-wrapper script with a specified interval (hourly, daily, weekly, monthly). Custom intervals are also possible, but not implemented at this time.
  2. rsnapshot-wrapper launches the rsnapshot-scheduler script, requesting a schedule operation for a given backup interval for all subdirectories found in the /etc/rsnapshot/hosts/ directory, a given subdirectory represents one host to back up.
  3. rsnapshot-scheduler scans /etc/rsnapshot/hosts/ subdirectories looking for configuration files, and checks if a given configuration uses specific interval - for example when a hourly interval is executed, script checks if retain hourly is present in the rsnapshot.conf configuration file.
  4. rsnapshot-scheduler checks if current backup interval for a given host is already scheduled using a pidfile in /run/rsnapshot-scheduler/ directory. If one is found, script finishes gracefully to not create duplicate backup jobs.
  5. If current interval is found and particular configuration is not disabled (file /etc/rsnapshot/hosts/<host>/stop|disable|disabled is absent), rsnapshot-scheduler creates a "backup job" for a given host. If at is installed, backup job will be added to the batch queue; otherwise, a background instance of rsnapshot-scheduler will be started with a random short sleep interval to not create high load spikes on the backup machine when multiple backups are scheduled at the same time.
  6. If at is installed, it will start backup jobs in order depending on the current system load (you can use the debops.atd role to manage that). Depending on available CPU cores and system load, backups might be done within the selected interval (hourly, for example). If not, duplicate backup jobs won't be created as long as the previous backup job is queued.
  7. On the next specified interval, cron will run the rsnapshot-scheduler again, scheduling new backup jobs.

How to backup hosts outside of Ansible cluster

In addition to backing up hosts under Ansible control, you might want to create configuration for backing up other hosts, which you don't want to configure directly (or can't). For this situation, you can use perform the steps described below to prepare the hosts for periodic snapshotting.

Things to set up on external host

For practical reasons, rsnapshot should use a root account directly on remote host. To make this configuration more secure, you can use rrsync Perl script provided with the rsync package, which lets you set up read-only access over SSH from remote hosts.

First, on Debian-based systems, install rsync package and extract provided script to a convenient directory:

sudo apt install rsync
sudo gzip -d -c /usr/share/doc/rsync/scripts/rrsync.gz > /usr/local/bin/rrsync
sudo chmod +x /usr/local/bin/rrsync

When the rrsync script is set up, you will have to add one of the rsnapshot SSH identities on the remote host, in the ~/.ssh/authorized_keys file of the root account. The default SSH identities are located in the ~/.ssh/id_rsnapshot*.pub files on the rsnapshot host. You should use the same SSH identity which you configured with a given host using the item.ssh_identity parameter, or id_rsnapshot if you want to use the default one.

At the same time you will configure this key to only allow for a specific rsync command. You should include configuration similar to this in /root/.ssh/authorized_keys, in one line:

no-pty,no-agent-forwarding,no-X11-forwarding,no-port-forwarding,command="ionice -c 3 nice /usr/local/bin/rrsync -ro /" ssh-rsa AAAAB3NzaC1yc2EAAAA...

The ionice and the nice commands will prevent rsync from hogging too much system resources during its operation.

This will allow read-only access to whole filesystem. After that, you can run the debops.rsnapshot Ansible role and it should correctly configure your rsnapshot client host to access external servers.

Fixing "stdin: is not a tty" issue

On default Debian installation there is a problem - when rsnapshot tries to connect to the server, shell might respond with a warning:

stdin: is not a tty

This will prompt rsnapshot to send an e-mail to system administrator with the response, which might get annoying after a while. To avoid that, open /root/.profile file on an external host and change line:

mesg n

to:

tty -s && mesg n

This will tell shell that it should check if connection is interactive before changing the terminal settings. This configuration is automatically applied on hosts managed by DebOps by the debops.root_account Ansible role.