restic: Add role+playbook for Restic backups

The `restic.yml` playbook applies the _restic_ role to hosts in the
_restic_ group.  The _restic_ role installs `restic` and creates a
systemd timer and service unit to run `restic backup` every day.

Restic doesn't really have a configuration file; all its settings are
controlled either by environment variables or command-line options. Some
options, such as the list of files to include in or exclude from
backups, take paths to files containing the values.  We can make use of
these to provide some configurability via Ansible variables.  The
`restic_env` variable is a map of environment variables and values to
set for `restic`.  The `restic_include` and `restic_exclude` variables
are lists of paths/patterns to include and exclude, respectively.
Finally, the `restic_password` variable contains the password to decrypt
the repository contents.  The password is written to a file and exposed
to the _restic-backup.service_ unit using [systemd credentials][0].

When using S3 or a compatible service for respository storage, Restic of
course needs authentication credentials.  These can be set using the
`restic_aws_credentials` variable.  If this variable is defined, it
should be a map containing the`aws_access_key_id` and
`aws_secret_access_key` keys, which will be written to an AWS shared
credentials file.  This file is then exposed to the
_restic-backup.service_ unit using [systemd credentials][0].

[0]: https://systemd.io/CREDENTIALS/

roles/restic/defaults/main.yml

@@ -0,0 +1,4 @@
+restic_env: {}
+restic_include:
+- /home
+restic_exclude: []

roles/restic/files/restic-backup.service

@@ -0,0 +1,12 @@
+[Unit]
+Description=Back up filesystem with restic
+
+[Service]
+Type=oneshot
+LoadCredential=restic.aws.credentials
+LoadCredential=restic.password
+Environment=AWS_SHARED_CREDENTIALS_FILE=%d/restic.aws.credentials
+Environment=RESTIC_PASSWORD_FILE=%d/restic.password
+Environment=XDG_CACHE_HOME=%C
+EnvironmentFile=-%E/restic/environment
+ExecStart=/usr/bin/restic backup --files-from %E/restic/include --exclude-file %E/restic/exclude --exclude-if-present .nobackup

roles/restic/files/restic-backup.timer

@@ -0,0 +1,11 @@
+[Unit]
+Description=Daily directory back up with restic
+
+[Timer]
+OnCalendar=daily
+RandomizedDelaySec=12h
+FixedRandomDelay=true
+Persistent=true
+
+[Install]
+WantedBy=default.target

roles/restic/handlers/main.yml

@@ -0,0 +1,8 @@
+- name: reload systemd
+  systemd:
+    daemon_reload: true
+
+- name: restart restic backup timer
+  systemd:
+    name: restic-backup.timer
+    state: restarted

roles/restic/tasks/main.yml

@@ -0,0 +1,106 @@
+- name: ensure restic is installed
+  package:
+    name: restic
+    state: present
+  tags:
+  - install
+
+- name: ensure restic configuration directory exists
+  file:
+    path: /etc/restic
+    owner: root
+    group: root
+    mode: u=rwx,go=rx
+    state: directory
+  tags:
+  - config
+
+- name: ensure restic environment is configured
+  template:
+    src: restic.env.j2
+    dest: /etc/restic/environment
+    owner: root
+    group: root
+    mode: u=rw,go=r
+  tags:
+  - config
+  - restic-environment
+- name: ensure restic file list is populated
+  template:
+    src: include.j2
+    dest: /etc/restic/include
+    owner: root
+    group: root
+    mode: u=rw,go=r
+  tags:
+  - config
+  - restic-include
+- name: ensure restic exclude list is populated
+  template:
+    src: exclude.j2
+    dest: /etc/restic/exclude
+    owner: root
+    group: root
+    mode: u=rw,go=r
+  tags:
+  - config
+  - restic-exclude
+
+- name: ensure restic password is set
+  copy:
+    content: >-
+      {{ restic_password }}
+    dest: /etc/credstore/restic.password
+    owner: root
+    group: root
+    mode: a=
+  diff: false
+  tags:
+  - config
+  - credentials
+- name: ensure restic aws credentials are set
+  template:
+    src: credentials.j2
+    dest: /etc/credstore/restic.aws.credentials
+    owner: root
+    group: root
+    mode: a=
+  diff: false
+  tags:
+  - config
+  - credentials
+
+- name: ensure restic-backup systemd service unit is installed
+  copy:
+    src: restic-backup.service
+    dest: /etc/systemd/system/restic-backup.service
+    owner: root
+    group: root
+    mode: u=rw,go=r
+  tags:
+  - systemd
+  notify:
+  - reload systemd
+  - restart restic backup timer
+- name: ensure restic-backup systemd timer unit is installed
+  copy:
+    src: restic-backup.timer
+    dest: /etc/systemd/system/restic-backup.timer
+    owner: root
+    group: root
+    mode: u=rw,go=r
+  tags:
+  - systemd
+
+- name: ensure restic-backup timer is enabled
+  systemd:
+    name: restic-backup.timer
+    enabled: true
+  tags:
+  - service
+- name: ensure restic-backup timer is running
+  systemd:
+    name: restic-backup.timer
+    state: started
+  tags:
+  - service

roles/restic/templates/credentials.j2

@@ -0,0 +1,6 @@
+[default]
+{% if restic_aws_credentials is defined %}
+{% for key, value in restic_aws_credentials.items() %}
+{{ key }} = {{ value }}
+{% endfor %}
+{% endif %}

roles/restic/templates/exclude.j2

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+{% for path in restic_exclude %}
+{{ path }}
+{% endfor %}

roles/restic/templates/include.j2

@@ -0,0 +1,3 @@
+{% for path in restic_include %}
+{{ path }}
+{% endfor %}

roles/restic/templates/restic.env.j2

@@ -0,0 +1,3 @@
+{% for key, value in _restic_env.items() %}
+{{ key }}={{ value }}
+{% endfor %}

roles/restic/vars/main.yml

@@ -0,0 +1,2 @@
+restic_default_env: {}
+_restic_env: '{{ restic_default_env|combine(restic_env) }}'