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Server Farmer backup collector


Distributed backup is one of the key functionalities of Server Farmer.

All hosts with installed Server Farmer, unless explicitly disabled, are doing their own backup (to specified directory on local drive, using sf-backup extension), which is then pulled using scp by backup collector host (which is responsible for long-term backup storage).

This part of backup documentation describes only collector/storage aspects. See sf-backup repository for details about the backup process itself.

Adding new servers to backup collector

New servers are added using script, which requires that added server has already installed dedicated ssh key for backup system user.

Usually all this process is wrapped by script from sm-farm-manager extension, which is the primary script for adding new servers to the farm.

Types of backup collectors

There are 4 types of backup collectors:

  1. Standalone - in this default scenario, farm manager is also the only backup collector (except possibly blind slaves). It is responsible for:
  • managing backup.hosts file (and associated ssh keys)
  • fetching backup archives from managed hosts
  • all possible further actions on fetched backups (statistics, transformations etc. - out of scope)
  1. Master - responsible only for the management part, while backup.hosts and ssh keys are sent to slave collector(s) after each update, using script.

  2. Slave - responsible only for actual fetching backup archives and further processing. Registered in collector.hosts file on master collector. Typically there is only one slave collector (all of them share the same backup.hosts file and would fetch the same data, so multiple slaves are mostly used in tricky and very rare network setups).

  3. Blind slave - like slave, but not registered in collector.hosts file, instead updated manually, and responsible for backups of some group of servers only. Such configuration is used mainly for commercial customers, who want to have all their backup stored in separate place.

backup.hosts file format

backup.hosts (as well as collector.hosts) is simply a text file with list of hostnames, possibly including port numbers, one per line:


Empty lines and lines starting with # character are ignored.

How backup collector backups itself

Backup collector, just like any other host, is responsible for its own backup.

Then, if its hostname is found in backup.hosts file, its backup is moved locally (instead of scp) to storage directory tree.

In some special scenarios, you can remove backup collector hostname from backup.hosts file (this is used mostly in high-compliance setups, in combination with push-to-collector (where farm manager and backup collector are sending their own encrypted backups to another host).

Backup storage directory tree format

All fetched backup archives are stored inside /srv/mounts/backup/remote directory (you can't change it, but it can be a symlink). Default directory tree structure looks like this:

                          ^                      ^        ^
                          hostname (no port)     date     file

If this is not enough, since you eg. need to store backups from each hour, you can extend this structure using /etc/local/.config/backup.index file, which should contain the date mask, eg.:


Backup transfer process

Backup collector fetches backup files from remote hosts using scp and dedicated ssh keys (separate key for each host), for backup system user.

Push-to-collector mode

In default scenario, backup collector has full shell access to managed hosts, as backup system user, including to farm manager. In high-compliance setups, eg. PCI DSS, this is not acceptable, as this is just one step away from having access to management ssh keys located on farm manager.

Because of that, script cron/ in sf-backup extension allows transferring farm manager encrypted backups in other direction: from farm manager to backup collector. This way, backup collector no longer needs ssh access to farm manager, which .


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