How Do I Use Salt States?

Simplicity, Simplicity, Simplicity

Many of the most powerful and useful engineering solutions are founded on simple principles. The Salt SLS system strives to do just that. K.I.S.S.

The core of the Salt State system is the SLS, or the SaLt State file. The SLS is a representation of the state in which a system should be in, and is set up to contain this data simply. This is often called configuration management.

It is All Just Data

Before delving into the particulars, it will help to understand that the SLS is just a data structure under the hood. While understanding that the SLS is just a data structure is not at all critical to understand to make use Salt States, it should help bolster the understanding of where the real power is.

SLS files are therefore, in reality, just dictionaries, lists, strings, and numbers. By using this approach Salt can be much more flexible. As someone writes more state files, it becomes clear exactly what is being written. The result is a system that is easy to understand, yet grows with the needs of the admin or developer.

In the section titled "State Data Structures" a reference exists, explaining in depth how the data is laid out.

Default Data - YAML

By default Salt represents the SLS data in what is one of the simplest serialization formats available - YAML.

A typical SLS file will often look like this in YAML:

 apache:
   pkg:
     - installed
   service:
     - running
     - require:
       - pkg: apache

This SLS data will ensure that the package named apache is installed, and that the apache service is running. The components can be explained in a simple way.

The first line is the ID for a set of data, and it is called the ID Declaration. This ID sets the name of the thing that needs to be manipulated.

The second and fourth lines are the start of the State Declarations, so they are using the pkg and service states respectively. The pkg state manages a software package to get installed via the system's native package manager, and the service state manages a system daemon. Below the pkg and service lines are the function to run. This function defines what state the named package and service should be in. Here the package is to be installed, and the service should be running.

Finally, on line 6, is the word require. This is called a Requisite Statement, and it makes sure that the Apache service is only started after the successful installation of the apache package.

Adding Configs and Users

When setting up a service like an Apache web server, many more components may need to be added. The Apache configuration file will most likely be managed, and a user and group may need to be set up.

 apache:
   pkg:
     - installed
   service:
     - running
     - watch:
       - pkg: apache
       - file: /etc/httpd/conf/httpd.conf
       - user: apache
   user.present:
     - uid: 87
     - gid: 87
     - home: /var/www/html
     - shell: /bin/nologin
     - require:
       - group: apache
   group.present:
     - gid: 87
     - require:
       - pkg: apache

 /etc/httpd/conf/httpd.conf:
   file.managed:
     - source: salt://apache/httpd.conf
     - user: root
     - group: root
     - mode: 644

This SLS data greatly extends the first example, and includes a config file, a user, a group and new requisite statement: watch.

Adding more states is easy, since the new user and group states are under the Apache ID, the user and group will be the Apache user and group. The require statements will make sure that the user will only be made after the group, and that the group will be made only after the Apache package is installed.

Next,the require statement under service was changed to watch, and is now watching 3 states instead of just one. The watch statement does the same thing as require, making sure that the other states run before running the state with a watch, but it adds an extra component. The watch statement will run the state's watcher function if any of the watched states changed anything. So if the package was updated, the config file changed, or the user uid modified, then the service state's watcher will be run. The service state's watcher just restarts the service, so in this case, a change in the config file will also trigger a restart of the respective service.

Moving Beyond a Single SLS

When setting up Salt States, more than one SLS will need to be used. The above examples were just in a single SLS file, but more than one SLS file can be combined to build out a State Tree. The above example also references a file with a strange source - salt://apache/httpd.conf. That file will need to be available as well.

The SLS files are laid out in a directory on the Salt master. Files are laid out as just files. A SLS is just a file and files to download are just files.

The Apache example would be laid out in the root of the Salt file server like this:

apache/init.sls
apache/httpd.conf

So the httpd.conf is just a file in the apache directory, and is referenced directly.

But with more than a single SLS file, more components can be added to the toolkit, consider this SSH example:

ssh/init.sls:

 openssh-client:
   pkg.installed

 /etc/ssh/ssh_config:
   file.managed:
     - user: root
     - group: root
     - mode: 644
     - source: salt://ssh/ssh_config
     - require:
       - pkg: openssh-client

ssh/server.sls:

 include:
   - ssh

 openssh-server:
   pkg.installed

 sshd:
   service.running:
     - require:
       - pkg: openssh-client
       - pkg: openssh-server
       - file: /etc/ssh/banner
       - file: /etc/ssh/sshd_config

 /etc/ssh/sshd_config:
   file.managed:
     - user: root
     - group: root
     - mode: 644
     - source: salt://ssh/sshd_config
     - require:
       - pkg: openssh-server

 /etc/ssh/banner:
   file:
     - managed
     - user: root
     - group: root
     - mode: 644
     - source: salt://ssh/banner
     - require:
       - pkg: openssh-server

Note

You may notice that we use two similar ways of denoting that a file is managed by Salt. In the /etc/ssh/sshd_config state section above, we use the file.managed state declaration whereas with the /etc/ssh/banner state section, we use the file state declaration and add a managed attribute to that state declaration. Both ways produce an identical result; the first way -- using file.managed -- is merely a shortcut.

Now our State Tree looks like this:

apache/init.sls
apache/httpd.conf
ssh/init.sls
ssh/server.sls
ssh/banner
ssh/ssh_config
ssh/sshd_config

This example now introduces the include statement. The include statement includes another SLS file so that components found in it can be required, watched or as will soon be demonstrated - extended.

The include statement allows for states to be cross linked. When an SLS has an include statement it is literally extended to include the contents of the included SLS files.

Extending Included SLS Data

Sometimes SLS data needs to be extended. Perhaps the apache service needs to watch additional resources, or under certain circumstances a different file needs to be placed.

These examples will add more watchers to apache and change the ssh banner.

ssh/custom-server.sls:

 include:
   - ssh.server

 extend:
   /etc/ssh/banner:
     file:
       - source: salt://ssh/custom-banner

python/mod_python.sls:

 include:
   - apache

 extend:
   apache:
     service:
       - watch:
         - pkg: mod_python

 mod_python:
   pkg.installed

The custom-server.sls file uses the extend statement to overwrite where the banner is being downloaded from, and therefore changing what file is being used to configure the banner.

In the new mod_python SLS the mod_python package is added, but more importantly the apache service was extended to also watch the mod_python package.

Using extend with require or watch

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

Understanding the Render System

Since the SLS data is just plain old data, it does not need to be represented with YAML. Salt defaults to YAML because it is very straightforward and easy to learn and use. But the SLS files can be rendered from almost any imaginable medium, so long as a renderer module is provided.

The default rendering system is the yaml_jinja renderer. The yaml_jinja renderer will first pass the template through the Jinja2 templating system, and then through the YAML parser. The benefit here is that full programming constructs are available when creating SLS files.

Other renderers available are yaml_mako and yaml_wempy which each use the Mako or Wempy templating system respectively rather than the jinja templating system, and more notably, the pure Python or py renderer. The py renderer allows for SLS files to be written in pure Python, allowing for the utmost level of flexibility and power when preparing SLS data.

Getting to Know the Default - yaml_jinja

The default renderer - yaml_jinja, allows for the use of the jinja templating system. A guide to the Jinja templating system can be found here: http://jinja.pocoo.org/docs

When working with renderers a few very useful bits of data are passed in. In the case of templating engine based renderers, three critical components are available, salt, grains, and pillar. The salt object allows for any Salt function to be called from within the template, and grains allows for the Grains to be accessed from within the template. A few examples:

apache/init.sls:

 apache:
   pkg.installed:
     {% if grains['os'] == 'RedHat'%}
     - name: httpd
     {% endif %}
   service.running:
     {% if grains['os'] == 'RedHat'%}
     - name: httpd
     {% endif %}
     - watch:
       - pkg: apache
       - file: /etc/httpd/conf/httpd.conf
       - user: apache
   user.present:
     - uid: 87
     - gid: 87
     - home: /var/www/html
     - shell: /bin/nologin
     - require:
       - group: apache
   group.present:
     - gid: 87
     - require:
       - pkg: apache

 /etc/httpd/conf/httpd.conf:
   file.managed:
     - source: salt://apache/httpd.conf
     - user: root
     - group: root
     - mode: 644

This example is simple. If the os grain states that the operating system is Red Hat, then the name of the Apache package and service needs to be httpd.

A more aggressive way to use Jinja can be found here, in a module to set up a MooseFS distributed filesystem chunkserver:

moosefs/chunk.sls:

 include:
   - moosefs

 {% for mnt in salt['cmd.run']('ls /dev/data/moose*').split() %}
 /mnt/moose{{ mnt[-1] }}:
   mount.mounted:
     - device: {{ mnt }}
     - fstype: xfs
     - mkmnt: True
   file.directory:
     - user: mfs
     - group: mfs
     - require:
       - user: mfs
       - group: mfs
 {% endfor %}

 '/etc/mfshdd.cfg':
   file.managed:
     - source: salt://moosefs/mfshdd.cfg
     - user: root
     - group: root
     - mode: 644
     - template: jinja
     - require:
       - pkg: mfs-chunkserver

 '/etc/mfschunkserver.cfg':
   file.managed:
     - source: salt://moosefs/mfschunkserver.cfg
     - user: root
     - group: root
     - mode: 644
     - template: jinja
     - require:
       - pkg: mfs-chunkserver

 mfs-chunkserver:
   pkg:
     - installed
 mfschunkserver:
   service:
     - running
     - require:
 {% for mnt in salt['cmd.run']('ls /dev/data/moose*') %}
       - mount: /mnt/moose{{ mnt[-1] }}
       - file: /mnt/moose{{ mnt[-1] }}
 {% endfor %}
       - file: /etc/mfschunkserver.cfg
       - file: /etc/mfshdd.cfg
       - file: /var/lib/mfs

This example shows much more of the available power provided by Jinja. Multiple for loops are used to dynamically detect available hard drives and set them up to be mounted, and the salt object is used multiple times to call shell commands to gather data.

Introducing the Python Renderer

Sometimes the chosen default renderer might not have enough logical power to accomplish the needed task. When this happens, the Python renderer can be used. Normally a YAML renderer should be used for the majority of SLS files, but a SLS file set to use another renderer can be easily added to the tree.

This example shows a very basic Python SLS file:

python/django.sls:

 #!py

 def run():
     '''
     Install the django package
     '''
     return {'include': ['python'],
             'django': {'pkg': ['installed']}}

This is a very simple example, the first line has a SLS shebang line that tells Salt to not use the default renderer, but to use the py renderer. Then the run function is defined, the return value from the run function must be a Salt friendly data structure, or better known as a Salt HighState data structure.

This Python example would look like this if it were written in YAML:

 include:
   - python

 django:
   pkg.installed

This clearly illustrates, that not only is using the YAML renderer a wise decision as the default, but that unbridled power can be obtained where needed by using a pure Python SLS.

Running and debugging salt states.

Once the rules in an SLS are ready, they need to be tested to ensure they work properly. To invoke the rules, simply execute salt '*' state.highstate on the command line. If you get back just the hostnames with a : after, but no return, chances are there is a problem with the one or more of the sls files. Use the salt-call command: salt-call state.highstate -l debug and examine the output for errors. This should help troubleshoot the issue. The minions can also be started in the foreground in debug mode. Start the minion in debug mode with: salt-minion -l debug.

Now onto the States tutorial, part 1.