States tutorial, part 3 - Templating, Includes, Extends¶

Note

This tutorial builds on topics covered in part 1 and part 2. It is recommended that you begin there.

This part of the tutorial will cover more advanced templating and configuration techniques for sls files.

Templating SLS modules¶

SLS modules may require programming logic or inline execution. This is accomplished with module templating. The default module templating system used is Jinja2 and may be configured by changing the renderer value in the master config.

All states are passed through a templating system when they are initially read. To make use of the templating system, simply add some templating markup. An example of an sls module with templating markup may look like this:

{% for usr in ['moe','larry','curly'] %}
{{ usr }}:
  user.present
{% endfor %}

This templated sls file once generated will look like this:

moe:
  user.present
larry:
  user.present
curly:
  user.present

Here's a more complex example:

# Comments in yaml start with a hash symbol.
# Since jinja rendering occurs before yaml parsing, if you want to include jinja
# in the comments you may need to escape them using 'jinja' comments to prevent
# jinja from trying to render something which is not well-defined jinja.
# e.g.
# {# iterate over the Three Stooges using a {% for %}..{% endfor %} loop
# with the iterator variable {{ usr }} becoming the state ID. #}
{% for usr in 'moe','larry','curly' %}
{{ usr }}:
  group:
    - present
  user:
    - present
    - gid_from_name: True
    - require:
      - group: {{ usr }}
{% endfor %}

Using Grains in SLS modules¶

Often times a state will need to behave differently on different systems. Salt grains objects are made available in the template context. The grains can be used from within sls modules:

apache:
  pkg.installed:
    {% if grains['os'] == 'RedHat' %}
    - name: httpd
    {% elif grains['os'] == 'Ubuntu' %}
    - name: apache2
    {% endif %}

Using Environment Variables in SLS modules¶

You can use salt['environ.get']('VARNAME') to use an environment variable in a Salt state.

MYENVVAR="world" salt-call state.template test.sls

 Create a file with contents from an environment variable:
file.managed:
  - name: /tmp/hello
  - contents: {{ salt['environ.get']('MYENVVAR') }}

Error checking:

{% set myenvvar = salt['environ.get']('MYENVVAR') %}
{% if myenvvar %}

Create a file with contents from an environment variable:
  file.managed:
    - name: /tmp/hello
    - contents: {{ salt['environ.get']('MYENVVAR') }}

{% else %}

Fail - no environment passed in:
  test:
    A. fail_without_changes

{% endif %}

Calling Salt modules from templates¶

All of the Salt modules loaded by the minion are available within the templating system. This allows data to be gathered in real time on the target system. It also allows for shell commands to be run easily from within the sls modules.

The Salt module functions are also made available in the template context as salt:

The following example illustrates calling the group_to_gid function in the file execution module with a single positional argument called some_group_that_exists.

moe:
  user.present:
    - gid: {{ salt['file.group_to_gid']('some_group_that_exists') }}

One way to think about this might be that the gid key is being assigned a value equivelent to the following python pseudo-code:

import salt.modules.file
file.group_to_gid('some_group_that_exists')

Note that for the above example to work, some_group_that_exists must exist before the state file is processed by the templating engine.

Below is an example that uses the network.hw_addr function to retrieve the MAC address for eth0:

salt['network.hw_addr']('eth0')

To examine the possible arguments to each execution module function, one can examine the module reference documentation </ref/modules/all>:

Advanced SLS module syntax¶

Lastly, we will cover some incredibly useful techniques for more complex State trees.

Include declaration¶

A previous example showed how to spread a Salt tree across several files. Similarly, requisites span multiple files by using an Include declaration. For example:

python/python-libs.sls:

python-dateutil:
  pkg.installed

python/django.sls:

include:
  - python.python-libs

django:
  pkg.installed:
    - require:
      - pkg: python-dateutil

Extend declaration¶

You can modify previous declarations by using an Extend declaration. For example the following modifies the Apache tree to also restart Apache when the vhosts file is changed:

apache/apache.sls:

apache:
  pkg.installed

apache/mywebsite.sls:

include:
  - apache.apache

extend:
  apache:
    service:
      - running
      - watch:
        - file: /etc/httpd/extra/httpd-vhosts.conf

/etc/httpd/extra/httpd-vhosts.conf:
  file.managed:
    - source: salt://apache/httpd-vhosts.conf

Using extend with require or watch

The extend statement works differently for require or watch. It appends to, rather than replacing the requisite component.

Name declaration¶

You can override the ID declaration by using a Name declaration. For example, the previous example is a bit more maintainable if rewritten as follows:

apache/mywebsite.sls:

include:
  - apache.apache

extend:
  apache:
    service:
      - running
      - watch:
        - file: mywebsite

mywebsite:
  file.managed:
    - name: /etc/httpd/extra/httpd-vhosts.conf
    - source: salt://apache/httpd-vhosts.conf

Names declaration¶

Even more powerful is using a Names declaration to override the ID declaration for multiple states at once. This often can remove the need for looping in a template. For example, the first example in this tutorial can be rewritten without the loop:

stooges:
  user.present:
    - names:
      - moe
      - larry
      - curly

Next steps¶

In part 4 we will discuss how to use salt's file_roots to set up a workflow in which states can be "promoted" from dev, to QA, to production.