TOFS: A pattern for using SaltStack

Table 1. Authors
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.

1. 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.

2. 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.

3. 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.

3.1. 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:

Directory and file tree for NTP
/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:

/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 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

3.2. Template Override

If the customization based on pillar data is not enough, we can override the template by creating a new one.

/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.

3.3. 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.

Directory and file tree for the files sub-directory
/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.

/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

3.4. 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/macros.jinja' import files_switch %}

Configure NTP:
  file.managed:
    - name: {{ ntp.config }}
    - template: jinja
    - source: {{ files_switch(
                  salt['config.get'](
                      tplroot ~ ':tofs:files:Configure NTP',
                      ['/etc/ntp.conf.jinja']
                  )
            ) }}
    - watch_in:
      - service: Enable and start NTP service
    - require:
      - pkg: Install NTP package

  • This uses config.get, searching for nfs:tofs:files:Configure NTP to determine the list of template files to use.

  • If this does not yield any results, the default of ['/etc/ntp.conf.jinja'] will be used.

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

/srv/saltstack/salt-formulas/ntp-saltstack-formula/ntp/macros.jinja
{%- macro files_switch(files,
                       default_files_switch=['id', 'os_family'],
                       indent_width=6) %}
  {#-
    Returns a valid value for the "source" parameter of a "file.managed"
    state function. This makes easier the usage of the Template Override and
    Files Switch (TOFS) pattern.

    Params:
      * files: ordered list of files to look for
      * default_files_switch: if there's no pillar
        '<tplroot>:tofs:files_switch' this is the ordered list of grains to
        use as selector switch of the directories under
        "<path_prefix>/files"
      * indent_witdh: indentation of the result value to conform to YAML

    Example (based on a `tplroot` of `xxx`):

    If we have a state:

      Deploy configuration:
        file.managed:
          - name: /etc/yyy/zzz.conf
          - source: {{ files_switch(
                          salt['config.get'](
                              tplroot ~ ':tofs:files:Deploy configuration',
                              ['/etc/yyy/zzz.conf', '/etc/yyy/zzz.conf.jinja']
                          )
                    ) }}
          - template: jinja

    In a minion with id=theminion and os_family=RedHat, it's going to be
    rendered as:

      Deploy configuration:
        file.managed:
          - name: /etc/yyy/zzz.conf
          - source:
            - salt://xxx/files/theminion/etc/yyy/zzz.conf
            - salt://xxx/files/theminion/etc/yyy/zzz.conf.jinja
            - salt://xxx/files/RedHat/etc/yyy/zzz.conf
            - salt://xxx/files/RedHat/etc/yyy/zzz.conf.jinja
            - salt://xxx/files/default/etc/yyy/zzz.conf
            - salt://xxx/files/default/etc/yyy/zzz.conf.jinja
          - template: jinja
  #}
  {#- Get the `tplroot` from `tpldir` #}
  {%- set tplroot = tpldir.split('/')[0] %}
  {%- set path_prefix = salt['config.get'](tplroot ~ ':tofs:path_prefix', tplroot) %}
  {%- set files_dir = salt['config.get'](tplroot ~ ':tofs:dirs:files', 'files') %}
  {%- set files_switch_list = salt['config.get'](
      tplroot ~ ':tofs:files_switch',
      default_files_switch
  ) %}
  {#- Only add to [''] when supporting older TOFS implementations #}
  {%- for path_prefix_ext in [''] %}
    {%- set path_prefix_inc_ext = path_prefix ~ path_prefix_ext %}
    {#- For older TOFS implementation, use `files_switch` from the pillar #}
    {#- Use the default, new method otherwise #}
    {%- set fsl = salt['pillar.get'](
        tplroot ~ path_prefix_ext|replace('/', ':') ~ ':files_switch',
        files_switch_list
    ) %}
    {#- Append an empty value to evaluate as `default` in the loop below #}
    {%- if '' not in fsl %}
      {%- do fsl.append('') %}
    {%- endif %}
    {%- for fs in fsl %}
      {%- for file in files %}
        {%- if fs %}
          {%- set fs_dir = salt['config.get'](fs, fs) %}
        {%- else %}
          {%- set fs_dir = salt['config.get'](tplroot ~ ':tofs:dirs:default', 'default') %}
        {%- endif %}
        {%- set url = '- salt://' ~ '/'.join([
            path_prefix_inc_ext,
            files_dir,
            fs_dir,
            file.lstrip('/')
        ]) %}
{{ url | indent(indent_width, true) }}
      {%- endfor %}
    {%- endfor %}
  {%- endfor %}
{%- endmacro %}

3.5. How to customise the source further

Scenario for the examples below

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 (default)
    - 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

3.5.1. Customise files

The files portion can be customised:

Customise files
ntp:
  tofs:
    dirs:
      files: files_alt

Resulting in:

source with files customised
    - 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

3.5.2. Customise the use of grains

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

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

Resulting in:

source with grains customised
    - 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

3.5.3. Customise the default path

The default portion of the path can be customised:

Customise default directory
ntp:
  tofs:
    dirs:
      default: default_alt

Resulting in:

source with default directory customised
    - source:
      ...
      - salt://ntp/files/default_alt/etc/ntp.conf.jinja

3.5.4. Customise the list of template files

The list of template files can be given:

Customise template files
ntp:
  tofs:
    files:
      Configure NTP:
        - '/etc/ntp.conf.jinja'
        - '/etc/ntp.conf_alt.jinja'

Resulting in:

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