Borg ansible role

2021-05-02 - The ansible role I wrote to manage my borg backups
Tags: ansible backups

Introduction

I have been managing my personal infrastructure with ansible for a few years and used borg to backup my servers for many more.

My ansible git repository is not published for privacy and confidentiality reasons but this week-end I decided to finally take the time to cleanup the code and publish this role. Thanks to git filter-branch --subdirectory-filter roles/borg --prune-empty -- --all I managed to extract the folder of my ansible repository and turn it into a submodule.

I wanted a role to easily manage my backups and did not find an existing one that satisfied me. A mandatory feature for me was the ability to configure a client in only one place without having to configure a server : the server configuration will be derived from the clients that need to use it as a backup target. Another mandatory feature is the validation of host_vars which virtually no role in the wild ever does… So I wrote mine.

This way configuring backups for a host named yen.adyxax.org is as simple as having the following host_vars :

julien@yen:~/git/adyxax/ansible$ cat host_vars/yen.adyxax.org
---
borg_server: cobsd-jde.nexen.net
borg_jobs:
  - { name: etc, path: "/etc", exclude: [ "/etc/firmware" ] }
  - name: gitea
    path: "/tmp/gitea.zip"
    pre_command: "echo '/usr/local/sbin/gitea -C /etc/gitea -c /etc/gitea/app.ini dump -f /tmp/gitea.zip' | su -l _gitea"
    post_command: "rm -f /tmp/gitea.zip"
  - { name: nethack, path: "/opt/nethack" }
  - { name: var_imap, path: "/var/imap" }
  - { name: var_spool_imap, path: "/var/spool/imap" }
...

Which can be used in a simple playbook like :

julien@yen:~/git/adyxax/ansible$ cat setup.yml
---
- name: Gather facts
  hosts: all
  tags: always
  tasks:
    - name: Gather facts
      setup:

- name: Enforce every configurations
  hosts: all
  roles:
    -  {  role:  borg,   tags: [ 'borg' ] }
...

Configuration

First of all you only need to configure hosts that are backup clients. There are several host_vars you can define to this effect :

To be valid a borg job entry needs to have a name and exactly one of path or command_to_pipe key.

Jobs examples

Here are some job examples :

What the role does

On the servers

On servers, the role creates a borg user with /srv/borg as a home directory where backups will be stored. For each client, a line in the borg user’s authorized_keys file is generated to enforce and limit access to only one clients' repository.

On the clients

On clients, the role creates a borg ssh key for the root user and generates a backup script in /usr/local/bin/adyxax_backup.sh. The role also adds a cron job that will run the backup script each nigh. Lastly it makes sure the client’s borg repository is properly initialised on the server.

Action plugins

There is an action plugin that validates host_vars types and values for each borg role variable, and another that parses the borg_server entries from all host_vars and set a borg fact for both machines to be backed up and for machines that are specified as backup targets (so that they do not require any manual configuration or variables). This action plugin also enforces the job rules to make sure those are valid and without ambiguities.

Ansible fact

There is a fact script deployed on each server. It is used to retrieve the ssh public key of clients or the repository status of servers and used in tasks.

Usefull command:

Manually schedule a backup run :

ansible all -i hosts -m shell -a "/usr/local/bin/adyxax_backup.sh"