The Magic of Pillar Targeting In SaltStack

Overview

In the course of using salt for all sorts of use cases I happened upon a particular pattern of using the states top file that, in my opinionated view, is the most elegant way.

Of the many ways targeting can be done in the states top file (see the SaltStack Documentation), the one I’m writing about here is the pillar target type.

Basic States and Top File Setup

Let’s say we have three minions called minion1, minion2, and minion3, and we have the breakfast.sls and dinner.sls states to deploy on them. Where our states are:

Breakfast:

{{ sls }} - write out the breakfast menu: 
  file.managed: 
    - name: /tmp/breakfast.txt 
    - contents: | 
        eggs: scrambled 
        meats: 
          - sausage 
          - bacon 
        sides: 
          spam: gross 
          beans: baked

Dinner:

{{ sls }} - write out the dinner menu: 
  file.managed: 
    - name: /tmp/dinner.txt 
    - contents: | 
        eggs: poached 
        seafood: lobster 
        other: 
          - truffle pate 
          - mornay sauce 
        sides: 
          spam: delicious 
          eggs: over easy

The most common form of targeting used in the states top file is globbing. So to deploy our states above on the minions, the states top file will look like:

'minion1': 
  - breakfast 
'minion2': 
  - dinner 
'minion3': 
  - breakfast 
  - dinner

Now in our states top file we have specified that minion1 is to run the breakfast.sls state, minion2 is to run the dinner.sls state, and minion3 is to run both breakfast and dinner.

Moving Data to Pillar

The above setup works just fine. But, it’s very rigid. Using the model above, If we were to add another minion that required a different value for dinner eggs, we would have to write a new state and add an entry to the top file. There’s no code reuse here.

Instead, lets move the data out of the states and into pillar by creating a couple of pillar files called breakfast-items.sls and dinner-items.sls:

breakfast_items: 
  menu: 
    egg: scrambled 
    meats: 
      - sausage 
      - bacon 
    sides: 
      spam: gross 
      beans: baked
dinner_items: 
  menu: 
    egg: poached 
    seafood: lobster 
  other: 
    - truffle pate 
    - mornay sauce 
  sides: 
    spam: delicious 
    egg: over easy

Now pillar files are also assigned to minions by way of a pillar top file. So we’ll need to make some similar entries as to what is in the states top file.

'minion1': 
  - breakfast-menu-items 
'minion2': 
  - dinner-menu-items 
'minion3': 
  - breakfast-menu-items 
  - dinner-menu-items

And of course, we need to update our breakfast.sls and dinner.sls states:

Breakfast:

{{ sls }} - write out the breakfast menu: 
  file.managed: 
    - name: /tmp/breakfast.txt 
    - contents_pillar: breakfast:menu

Dinner:

{{ sls }} - write out the dinner menu: 
  file.managed: 
    - name: /tmp/dinner.txt 
    - contents_pillar: dinner:menu

Magic

As can be seen above, the states top file and the pillar top file are very similar. Lets simplify the states top file by using pillar targeting.

The first step is to add a key to the pillar files that we can target against. Adding a key specific isn’t required, but IMO, it’s the best way. For this purpose, I like to add a key/value of install: true. It's easy to remember and easy to override in other pillars if necessary.

So breakfast-items.sls and dinner-items.sls become:

breakfast: 
  install: true 
  menu: 
    egg: scrambled 
    meats: 
      - sausage 
      - bacon 
    sides: 
      spam: gross 
      beans: baked
dinner: 
  install: true 
  menu: 
    egg: poached 
    seafood: lobster 
    other: 
      - truffle pate 
      - mornay sauce 
    sides: 
      spam: delicious 
      egg: over easy

And then our states top file becomes:

'breakfast:install:true' 
  - match: pillar 
  - breakfast 
'dinner:install:true' 
  - match: pillar 
  - dinner

… let the above sink in. You need one entry in the states top.sls for every state created. That's it.

Conclusion

While states and pillar files will proliferate in any environment. In my opinionated view, this is the easiest way of releaving overhead thoughts about what minions need to get which state in the top file.

Assignment happens automatically in most cases as almost all states (at least ones that I write) use data from pillars.

Originally published at https://smartaleksolutions.com on October 13, 2020.