PillarStack

Simple and flexible YAML ext_pillar which can read pillar from within pillar.

.. versionadded:: 2016.3.0

PillarStack is a custom saltstack ext_pillar which was inspired by varstack but is heavily based on Jinja2 for maximum flexibility.

Any issue should be reported to the upstream project at: https://github.com/bbinet/pillarstack/issues

It supports the following features:

• multiple config files that are jinja2 templates with support for pillar, __grains__, __salt__, __opts__ objects
• a config file renders as an ordered list of files (paths of these files are relative to the current config file)
• this list of files are read in ordered as jinja2 templates with support for stack, pillar, __grains__, __salt__, __opts__ objects
• all these rendered files are then parsed as yaml
• then all yaml dicts are merged in order with support for the following merging strategies: merge-first, merge-last, remove, and overwrite
• stack config files can be matched based on pillar, grains, or opts values, which make it possible to support kind of self-contained environments

Installation

PillarStack is already bundled with Salt since 2016.3.0 version so there is nothing to install from version 2016.3.0.

If you use an older Salt version or you want to override PillarStack with a more recent one, follow the installation procedure below.

Installing the PillarStack ext_pillar is as simple as dropping the stack.py file in the <extension_modules>/pillar directory (no external python module required), given that extension_modules is set in your salt-master configuration, see: http://docs.saltstack.com/en/latest/ref/configuration/master.html#extension-modules

Configuration in Salt

Like any other external pillar, its configuration takes place through the ext_pillar key in the master config file.

However, you can configure PillarStack in 3 different ways:

Single config file

This is the simplest option, you just need to set the path to your single PillarStack config file like below:

ext_pillar:
  - stack: /path/to/stack.cfg

List of config files

You can also provide a list of config files:

ext_pillar:
  - stack:
      - /path/to/stack1.cfg
      - /path/to/stack2.cfg

Select config files through grains|pillar|opts matching

You can also opt for a much more flexible configuration: PillarStack allows one to select the config files for the current minion based on matching values from either grains, or pillar, or opts objects.

Here is an example of such a configuration, which should speak by itself:

ext_pillar:
  - stack:
      pillar:environment:
        dev: /path/to/dev/stack.cfg
        prod: /path/to/prod/stack.cfg
      grains:custom:grain:
        value:
          - /path/to/stack1.cfg
          - /path/to/stack2.cfg
      opts:custom:opt:
        value: /path/to/stack0.cfg

PillarStack configuration files

The config files that are referenced in the above ext_pillar configuration are jinja2 templates which must render as a simple ordered list of yaml files that will then be merged to build pillar data.

The path of these yaml files must be relative to the directory of the PillarStack config file. These paths support unix style pathname pattern expansion through the Python glob module <https://docs.python.org/2/library/glob.html>.

The following variables are available in jinja2 templating of PillarStack configuration files:

• pillar: the pillar data (as passed by Salt to our ext_pillar function)
• minion_id: the minion id ;-)
• __opts__: a dictionary of mostly Salt configuration options
• __grains__: a dictionary of the grains of the minion making this pillar call
• __salt__: a dictionary of Salt module functions, useful so you don't have to duplicate functions that already exist (note: runs on the master)

So you can use all the power of jinja2 to build your list of yaml files that will be merged in pillar data.

For example, you could have a PillarStack config file which looks like:

$ cat /path/to/stack/config.cfg
core.yml
common/*.yml
osarchs/{{ __grains__['osarch'] }}.yml
oscodenames/{{ __grains__['oscodename'] }}.yml
{%- for role in pillar.get('roles', []) %}
roles/{{ role }}.yml
{%- endfor %}
minions/{{ minion_id }}.yml

And the whole directory structure could look like:

$ tree /path/to/stack/
/path/to/stack/
├── config.cfg
├── core.yml
├── common/
│   ├── xxx.yml
│   └── yyy.yml
├── osarchs/
│   ├── amd64.yml
│   └── armhf.yml
├── oscodenames/
│   ├── wheezy.yml
│   └── jessie.yml
├── roles/
│   ├── web.yml
│   └── db.yml
└── minions/
    ├── test-1-dev.yml
    └── test-2-dev.yml

Overall process

In the above PillarStack configuration, given that test-1-dev minion is an amd64 platform running Debian Jessie, and which pillar roles is ["db"], the following yaml files would be merged in order:

• core.yml
• common/xxx.yml
• common/yyy.yml
• osarchs/amd64.yml
• oscodenames/jessie.yml
• roles/db.yml
• minions/test-1-dev.yml

Before merging, every files above will be preprocessed as Jinja2 templates. The following variables are available in Jinja2 templating of yaml files:

• stack: the PillarStack pillar data object that has currently been merged (data from previous yaml files in PillarStack configuration)
• pillar: the pillar data (as passed by Salt to our ext_pillar function)
• minion_id: the minion id ;-)
• __opts__: a dictionary of mostly Salt configuration options
• __grains__: a dictionary of the grains of the minion making this pillar call
• __salt__: a dictionary of Salt module functions, useful so you don't have to duplicate functions that already exist (note: runs on the master)

So you can use all the power of jinja2 to build your pillar data, and even use other pillar values that has already been merged by PillarStack (from previous yaml files in PillarStack configuration) through the stack variable.

Once a yaml file has been preprocessed by Jinja2, we obtain a Python dict - let's call it yml_data - then, PillarStack will merge this yml_data dict in the main stack dict (which contains already merged PillarStack pillar data). By default, PillarStack will deeply merge yml_data in stack (similarly to the recurse salt pillar_source_merging_strategy), but 3 merging strategies are currently available for you to choose (see next section).

Once every yaml files have been processed, the stack dict will contain your whole own pillar data, merged in order by PillarStack. So PillarStack ext_pillar returns the stack dict, the contents of which Salt takes care to merge in with all of the other pillars and finally return the whole pillar to the minion.

Merging strategies

The way the data from a new yaml_data dict is merged with the existing stack data can be controlled by specifying a merging strategy. Right now this strategy can either be merge-last (the default), merge-first, remove, or overwrite.

Note that scalar values like strings, integers, booleans, etc. are always evaluated using the overwrite strategy (other strategies don't make sense in that case).

The merging strategy can be set by including a dict in the form of:

__: <merging strategy>

as the first item of the dict or list. This allows fine grained control over the merging process.

merge-last (default) strategy

If the merge-last strategy is selected (the default), then content of dict or list variables is merged recursively with previous definitions of this variable (similarly to the recurse salt pillar_source_merging_strategy). This allows for extending previously defined data.

merge-first strategy

If the merge-first strategy is selected, then the content of dict or list variables are swapped between the yaml_data and stack objects before being merged recursively with the merge-last previous strategy.

remove strategy

If the remove strategy is selected, then content of dict or list variables in stack are removed only if the corresponding item is present in the yaml_data dict. This allows for removing items from previously defined data.

overwrite strategy

If the overwrite strategy is selected, then the content of dict or list variables in stack is overwritten by the content of yaml_data dict. So this allows one to overwrite variables from previous definitions.

Merging examples

Let's go through small examples that should clarify what's going on when a yaml_data dict is merged in the stack dict.

When you don't specify any strategy, the default merge-last strategy is selected:

stack	yaml_data	stack (after merge)
users: tom: uid: 500 roles: - sysadmin root: uid: 0	users: tom: uid: 1000 roles: - developer mat: uid: 1001	users: tom: uid: 1000 roles: - sysadmin - developer mat: uid: 1001 root: uid: 0

Then you can select a custom merging strategy using the __ key in a dict:

stack	yaml_data	stack (after merge)
users: tom: uid: 500 roles: - sysadmin root: uid: 0	users: __: merge-last tom: uid: 1000 roles: - developer mat: uid: 1001	users: tom: uid: 1000 roles: - sysadmin - developer mat: uid: 1001 root: uid: 0
users: tom: uid: 500 roles: - sysadmin root: uid: 0	users: __: merge-first tom: uid: 1000 roles: - developer mat: uid: 1001	users: tom: uid: 500 roles: - developer - sysadmin mat: uid: 1001 root: uid: 0
users: tom: uid: 500 roles: - sysadmin root: uid: 0	users: __: remove tom: mat:	users: root: uid: 0
users: tom: uid: 500 roles: - sysadmin root: uid: 0	users: __: overwrite tom: uid: 1000 roles: - developer mat: uid: 1001	users: tom: uid: 1000 roles: - developer mat: uid: 1001

You can also select a custom merging strategy using a __ object in a list:

stack	yaml_data	stack (after merge)
users: - tom - root	users: - __: merge-last - mat	users: - tom - root - mat
users: - tom - root	users: - __: merge-first - mat	users: - mat - tom - root
users: - tom - root	users: - __: remove - mat - tom	users: - root
users: - tom - root	users: - __: overwrite - mat	users: - mat