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TOFS: A pattern for using SaltStack

Person Contact Date
Authored by Roberto Moreda moreda@allenta.com 29/12/2014
Modified by Daniel Dehennin daniel.dehennin@baby-gnu.org 07/02/2019
Modified by Imran Iqbal https://github.com/myii 23/02/2019

All that follows is a proposal based on my experience with SaltStack. The good thing of a piece of software like this is that you can "bend it" to suit your needs in many possible ways, and this is one of them. All the recommendations and thoughts are given "as it is" with no warranty of any type.

Table of Contents

Usage of values in pillar vs templates in file_roots

Among other functions, the master (or salt-master) serves files to the minions (or salt-minions). The file_roots is the list of directories used in sequence to find a file when a minion requires it: the first match is served to the minion. Those files could be state files or configuration templates, among others.

Using SaltStack is a simple and effective way to implement configuration management, but even in a non-multitenant scenario, it is not a good idea to generally access some data (e.g. the database password in our Zabbix server configuration file or the private key of our Nginx TLS certificate).

To avoid this situation we can use the pillar mechanism, which is designed to provide controlled access to data from the minions based on some selection rules. As pillar data could be easily integrated in the Jinja templates, it is a good mechanism to store values to be used in the final rendering of state files and templates.

There are a variety of approaches on the usage of pillar and templates as seen in the saltstack-formulas' repositories. Some developments stress the initial purpose of pillar data into a storage for most of the possible variables for a determined system configuration. This, in my opinion, is shifting too much load from the original template files approach. Adding up some non-trivial Jinja code as essential part of composing the state file definitely makes SaltStack state files (hence formulas) more difficult to read. The extreme of this approach is that we could end up with a new render mechanism, implemented in Jinja, storing everything needed in pillar data to compose configurations. Additionally, we are establishing a strong dependency with the Jinja renderer.

In opposition to the put the code in file_roots and the data in pillars approach, there is the pillar as a store for a set of key-values approach. A full-blown configuration file abstracted in pillar and jinja is complicated to develop, understand and maintain. I think a better and simpler approach is to keep a configuration file templated using just a basic (non-extensive but extensible) set of pillar values.

On the reusability of SaltStack state files

There is a brilliant initiative of the SaltStack community called salt-formulas. Their goal is to provide state files, pillar examples and configuration templates ready to be used for provisioning. I am a contributor for two small ones: zabbix-formula and varnish-formula.

The design guidelines for formulas are clear in many aspects and it is a recommended reading for anyone willing to write state files, even non-formulaic ones.

In the next section, I am going to describe my proposal to extend further the reusability of formulas, suggesting some patterns of usage.

The Template Override and Files Switch (TOFS) pattern

I understand a formula as a complete, independent set of SaltStack state and configuration template files sufficient to configure a system. A system could be something as simple as an NTP server or some other much more complex service that requires many state and configuration template files.

The customization of a formula should be done mainly by providing pillar data used later to render either the state or the configuration template files.

Example: NTP before applying TOFS

Let's work with the NTP example. A basic formula that follows the design guidelines has the following files and directories tree:

/srv/saltstack/salt-formulas/ntp-saltstack-formula/
  ntp/
    map.jinja
    init.sls
    conf.sls
    files/
      default/
        etc/
          ntp.conf.jinja

In order to use it, let's assume a masterless configuration and this relevant section of /etc/salt/minion:

pillar_roots:
  base:
    - /srv/saltstack/pillar
file_client: local
file_roots:
  base:
    - /srv/saltstack/salt
    - /srv/saltstack/salt-formulas/ntp-saltstack-formula
{#- /srv/saltstack/salt-formulas/ntp-saltstack-formula/ntp/map.jinja #}
{%- set ntp = salt['grains.filter_by']({
  'default': {
    'pkg': 'ntp',
    'service': 'ntp',
    'config': '/etc/ntp.conf',
  },
}, merge=salt['pillar.get']('ntp:lookup')) %}

In init.sls we have the minimal states required to have NTP configured. In many cases init.sls is almost equivalent to an apt-get install or a yum install of the package.

## /srv/saltstack/salt-formulas/ntp-saltstack-formula/ntp/init.sls
{%- from 'ntp/map.jinja' import ntp with context %}

Install NTP:
  pkg.installed:
    - name: {{ ntp.pkg }}

Enable and start NTP:
  service.running:
    - name: {{ ntp.service }}
    - enabled: True
    - require:
      - pkg: Install NTP package

In conf.sls we have the configuration states. In most cases, that is just managing configuration file templates and making them to be watched by the service.

## /srv/saltstack/salt-formulas/ntp-saltstack-formula/ntp/conf.sls
include:
  - ntp

{%- from 'ntp/map.jinja' import ntp with context %}

Configure NTP:
  file.managed:
    - name: {{ ntp.config }}
    - template: jinja
    - source: salt://ntp/files/default/etc/ntp.conf.jinja
    - watch_in:
      - service: Enable and start NTP service
    - require:
      - pkg: Install NTP package

Under files/default, there is a structure that mimics the one in the minion in order to avoid clashes and confusion on where to put the needed templates. There you can find a mostly standard template for the configuration file.

{#- /srv/saltstack/salt-formulas/ntp-saltstack-formula/ntp/files/default/etc/ntp.conf.jinja #}
{#- Managed by saltstack #}
{#- Edit pillars or override this template in saltstack if you need customization #}
{%- set settings = salt['pillar.get']('ntp', {}) %}
{%- set default_servers = ['0.ubuntu.pool.ntp.org',
                          '1.ubuntu.pool.ntp.org',
                          '2.ubuntu.pool.ntp.org',
                          '3.ubuntu.pool.ntp.org'] %}

driftfile /var/lib/ntp/ntp.drift
statistics loopstats peerstats clockstats
filegen loopstats file loopstats type day enable
filegen peerstats file peerstats type day enable
filegen clockstats file clockstats type day enable

{%- for server in settings.get('servers', default_servers) %}
server {{ server }}
{%- endfor %}

restrict -4 default kod notrap nomodify nopeer noquery
restrict -6 default kod notrap nomodify nopeer noquery

restrict 127.0.0.1
restrict ::1

With all this, it is easy to install and configure a simple NTP server by just running salt-call state.sls ntp.conf: the package will be installed, the service will be running and the configuration should be correct for most of cases, even without pillar data.

Alternatively, you can define a highstate in /srv/saltstack/salt/top.sls and run salt-call state.highstate.

## /srv/saltstack/salt/top.sls
base:
  '*':
    - ntp.conf

Customizing the formula just with pillar data, we have the option to define the NTP servers.

## /srv/saltstack/pillar/top.sls
base:
  '*':
    - ntp
## /srv/saltstack/pillar/ntp.sls
ntp:
  servers:
    - 0.ch.pool.ntp.org
    - 1.ch.pool.ntp.org
    - 2.ch.pool.ntp.org
    - 3.ch.pool.ntp.org

Template Override

If the customization based on pillar data is not enough, we can override the template by creating a new one in /srv/saltstack/salt/ntp/files/default/etc/ntp.conf.jinja

{#- /srv/saltstack/salt/ntp/files/default/etc/ntp.conf.jinja #}
{#- Managed by saltstack #}
{#- Edit pillars or override this template in saltstack if you need customization #}

{#- Some bizarre configurations here #}
{#- ... #}

{%- for server in settings.get('servers', default_servers) %}
server {{ server }}
{%- endfor %}

This way we are locally overriding the template files offered by the formula in order to make a more complex adaptation. Of course, this could be applied as well to any of the files, including the state files.

Files Switch

To bring some order into the set of template files included in a formula, as we commented, we suggest having a similar structure to a normal final file system under files/default.

We can make different templates coexist for different minions, classified by any grain value, by simply creating new directories under files. This mechanism is based on using values of some grains as a switch for the directories under files/.

If we decide that we want os_family as switch, then we could provide the formula template variants for both the RedHat and Debian families.

/srv/saltstack/salt-formulas/ntp-saltstack-formula/ntp/files/
  default/
    etc/
      ntp.conf.jinja
  RedHat/
    etc/
      ntp.conf.jinja
  Debian/
    etc/
      ntp.conf.jinja

To make this work we need a conf.sls state file that takes a list of possible files as the configuration template.

## /srv/saltstack/salt-formulas/ntp-saltstack-formula/ntp/conf.sls
include:
  - ntp

{%- from 'ntp/map.jinja' import ntp with context %}

Configure NTP:
  file.managed:
    - name: {{ ntp.config }}
    - template: jinja
    - source:
      - salt://ntp/files/{{ grains.get('os_family', 'default') }}/etc/ntp.conf.jinja
      - salt://ntp/files/default/etc/ntp.conf.jinja
    - watch_in:
      - service: Enable and start NTP service
    - require:
      - pkg: Install NTP package

If we want to cover the possibility of a special template for a minion identified by node01 then we could have a specific template in /srv/saltstack/salt/ntp/files/node01/etc/ntp.conf.jinja.

{#- /srv/saltstack/salt/ntp/files/node01/etc/ntp.conf.jinja #}
{#- Managed by saltstack #}
{#- Edit pillars or override this template in saltstack if you need customization #}

{#- Some crazy configurations here for node01 #}
{#- ... #}

To make this work we could write a specially crafted conf.sls.

## /srv/saltstack/salt-formulas/ntp-saltstack-formula/ntp/conf.sls
include:
  - ntp

{%- from 'ntp/map.jinja' import ntp with context %}

Configure NTP:
  file.managed:
    - name: {{ ntp.config }}
    - template: jinja
    - source:
      - salt://ntp/files/{{ grains.get('id') }}/etc/ntp.conf.jinja
      - salt://ntp/files/{{ grains.get('os_family') }}/etc/ntp.conf.jinja
      - salt://ntp/files/default/etc/ntp.conf.jinja
    - watch_in:
      - service: Enable and start NTP service
    - require:
      - pkg: Install NTP package

Using the files_switch macro

We can simplify the conf.sls with the new files_switch macro to use in the source parameter for the file.managed state.

## /srv/saltstack/salt-formulas/ntp-saltstack-formula/ntp/conf.sls
include:
  - ntp

{%- set tplroot = tpldir.split('/')[0] %}
{%- from 'ntp/map.jinja' import ntp with context %}
{%- from 'ntp/libtofs.jinja' import files_switch %}

Configure NTP:
  file.managed:
    - name: {{ ntp.config }}
    - template: jinja
    - source: {{ files_switch(['/etc/ntp.conf.jinja'],
                              lookup='Configure NTP'
                 )
              }}
    - watch_in:
      - service: Enable and start NTP service
    - require:
      - pkg: Install NTP package
  • This uses config.get, searching for ntp:tofs:source_files:Configure NTP to determine the list of template files to use.
  • If this returns a result, the default of ['/etc/ntp.conf.jinja'] will be appended to it.
  • If this does not yield any results, the default of ['/etc/ntp.conf.jinja'] will be used.

In libtofs.jinja, we define this new macro files_switch.

../template/libtofs.jinja

How to customise the source further

The examples below are based on an Ubuntu minion called theminion being configured via. pillar.

Using the default settings of the files_switch macro above, the source will be:

- source:
  - salt://ntp/files/theminion/etc/ntp.conf.jinja
  - salt://ntp/files/Debian/etc/ntp.conf.jinja
  - salt://ntp/files/default/etc/ntp.conf.jinja

Customise files

The files portion can be customised:

ntp:
  tofs:
    dirs:
      files: files_alt

Resulting in:

- source:
  - salt://ntp/files_alt/theminion/etc/ntp.conf.jinja
  - salt://ntp/files_alt/Debian/etc/ntp.conf.jinja
  - salt://ntp/files_alt/default/etc/ntp.conf.jinja

Customise the use of grains

Grains can be customised and even arbitrary paths can be supplied:

ntp:
  tofs:
    files_switch:
      - any/path/can/be/used/here
      - id
      - os
      - os_family

Resulting in:

- source:
  - salt://ntp/files/any/path/can/be/used/here/etc/ntp.conf.jinja
  - salt://ntp/files/theminion/etc/ntp.conf.jinja
  - salt://ntp/files/Ubuntu/etc/ntp.conf.jinja
  - salt://ntp/files/Debian/etc/ntp.conf.jinja
  - salt://ntp/files/default/etc/ntp.conf.jinja

Customise the default path

The default portion of the path can be customised:

ntp:
  tofs:
    dirs:
      default: default_alt

Resulting in:

- source:
  ...
  - salt://ntp/files/default_alt/etc/ntp.conf.jinja

Customise the list of source_files

The list of source_files can be given:

ntp:
  tofs:
    source_files:
      Configure NTP:
        - '/etc/ntp.conf_alt.jinja'

Resulting in:

- source:
  - salt://ntp/files/theminion/etc/ntp.conf_alt.jinja
  - salt://ntp/files/theminion/etc/ntp.conf.jinja
  - salt://ntp/files/Debian/etc/ntp.conf_alt.jinja
  - salt://ntp/files/Debian/etc/ntp.conf.jinja
  - salt://ntp/files/default/etc/ntp.conf_alt.jinja
  - salt://ntp/files/default/etc/ntp.conf.jinja

Note: This does not override the default value. Rather, the value from the pillar/config is prepended to the default.

Using sub-directories for components

If your formula is composed of several components, you may prefer to provides files under sub-directories, like in the systemd-formula.

/srv/saltstack/systemd-formula/
  systemd/
    init.sls
    libtofs.jinja
    map.jinja
    networkd/
      init.sls
      files/
        default/
          network/
            99-default.link
    resolved/
      init.sls
      files/
        default/
          resolved.conf
    timesyncd/
      init.sls
      files/
        Arch/
          resolved.conf
        Debian/
          resolved.conf
        default/
          resolved.conf
        Ubuntu/
          resolved.conf

For example, the following formula.component.config SLS:

{%- from "formula/libtofs.jinja" import files_switch with context %}

formula configuration file:
  file.managed:
    - name: /etc/formula.conf
    - user: root
    - group: root
    - mode: 644
    - template: jinja
    - source: {{ files_switch(['formula.conf'],
                              lookup='formula',
                              use_subpath=True
                 )
              }}

will be rendered on a Debian minion named salt-formula.ci.local as:

formula configuration file:
  file.managed:
    - name: /etc/formula.conf
    - user: root
    - group: root
    - mode: 644
    - template: jinja
    - source:
      - salt://formula/component/files/salt-formula.ci.local/formula.conf
      - salt://formula/component/files/Debian/formula.conf
      - salt://formula/component/files/default/formula.conf
      - salt://formula/files/salt-formula.ci.local/formula.conf
      - salt://formula/files/Debian/formula.conf
      - salt://formula/files/default/formula.conf