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States tutorial, part 2 - More Complex States, Requisites

doc/topics/tutorials/states_pt2.rst

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.. _tutorial-states-part-2:

========================================================= States tutorial, part 2 - More Complex States, Requisites

.. note::

This tutorial builds on topics covered in :ref:`part 1 <states-tutorial>`. It is
recommended that you begin there.

In the :ref:last part <states-tutorial> of the Salt States tutorial we covered the basics of installing a package. We will now modify our webserver.sls file to have requirements, and use even more Salt States.

Call multiple States

You can specify multiple :ref:state-declaration under an :ref:id-declaration. For example, a quick modification to our webserver.sls to also start Apache if it is not running:

.. code-block:: yaml :linenos: :emphasize-lines: 4,5

apache:
  pkg.installed: []
  service.running:
    - require:
      - pkg: apache

Try stopping Apache before running :py:func:state.apply <salt.modules.state.apply_> once again and observe the output.

.. note::

For those running RedhatOS derivatives (Centos, AWS), you will want to specify the
service name to be httpd. More on state service here, :mod:`service state
<salt.states.service>`.  With the example above, just add "- name: httpd"
above the require line and with the same spacing.

Require other states

We now have a working installation of Apache so let's add an HTML file to customize our website. It isn't exactly useful to have a website without a webserver so we don't want Salt to install our HTML file until Apache is installed and running. Include the following at the bottom of your webserver/init.sls file:

.. code-block:: yaml :linenos: :emphasize-lines: 7,11

apache:
  pkg.installed: []
  service.running:
    - require:
      - pkg: apache

/var/www/index.html:                        # ID declaration
  file:                                     # state declaration
    - managed                               # function
    - source: salt://webserver/index.html   # function arg
    - require:                              # requisite declaration
      - pkg: apache                         # requisite reference

line 7 is the :ref:id-declaration. In this example it is the location we want to install our custom HTML file. (Note: the default location that Apache serves may differ from the above on your OS or distro. /srv/www could also be a likely place to look.)

Line 8 the :ref:state-declaration. This example uses the Salt :mod:file state <salt.states.file>.

Line 9 is the :ref:function-declaration. The :func:managed function <salt.states.file.managed> will download a file from the master and install it in the location specified.

Line 10 is a :ref:function-arg-declaration which, in this example, passes the source argument to the :func:managed function <salt.states.file.managed>.

Line 11 is a :ref:requisite-declaration.

Line 12 is a :ref:requisite-reference which refers to a state and an ID. In this example, it is referring to the ID declaration from our example in :ref:part 1 <states-tutorial>. This declaration tells Salt not to install the HTML file until Apache is installed.

Next, create the index.html file and save it in the webserver directory:

.. code-block:: html

<!DOCTYPE html>
<html>
    <head><title>Salt rocks</title></head>
    <body>
        <h1>This file brought to you by Salt</h1>
    </body>
</html>

Last, call :func:state.apply <salt.modules.state.apply_> again and the minion will fetch and execute the :ref:highstate <running-highstate> as well as our HTML file from the master using Salt's File Server:

.. code-block:: bash

salt '*' state.apply

Verify that Apache is now serving your custom HTML.

.. admonition:: require vs. watch

There are two :ref:`requisite-declaration`, “require”, and “watch”. Not
every state supports “watch”. The :mod:`service state
<salt.states.service>` does support “watch” and will restart a service
based on the watch condition.

For example, if you use Salt to install an Apache virtual host
configuration file and want to restart Apache whenever that file is changed
you could modify our Apache example from earlier as follows:

.. code-block:: yaml
    :emphasize-lines: 1,2,3,10,11

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

    apache:
      pkg.installed: []
      service.running:
        - watch:
          - file: /etc/httpd/extra/httpd-vhosts.conf
        - require:
          - pkg: apache

If the pkg and service names differ on your OS or distro of choice you can
specify each one separately using a :ref:`name-declaration` which explained
in :ref:`Part 3 <tutorial-states-part-3>`.

Next steps

In :ref:part 3 <tutorial-states-part-3> we will discuss how to use includes, extends, and templating to make a more complete State Tree configuration.