States tutorial, part 3

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# States tutorial, part 3

Note

This tutorial builds on the topic covered in part1 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

## 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 %}

## 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`:

    {% for usr in 'moe','larry','curly' %}
    {{ usr }}:
      group:
        - present
      user:
        - present
        - gid: {{ salt['file.group_to_gid'](usr) }}
        - require:
          - group: {{ usr }}
    {% endfor %}

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

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

## 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, requisite references span multiple files by using an include declaration. For example:

`python/python-libs.sls`:

    python-dateutil:
      pkg.installed

`python/django.sls`:

    include:
      - 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

    extend:
      apache:
        service:
          - 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

    extend:
      apache:
        service:
          - 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

## Continue learning

The best way to continue learning about Salt States is to read through the reference documentation and to look through examples of existing state trees. You can find examples in the salt-states repository and please send a pull-request on GitHub with any state trees that you build and want to share!

If you have any questions, suggestions, or just want to chat with other people who are using Salt we have an active community.

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