State Enforcement

Salt offers an optional interface to manage the configuration or "state" of the Salt minions. This interface is a fully capable mechanism used to enforce the state of systems from a central manager.

State Management

State management, also frequently called Software Configuration Management (SCM), is a program that puts and keeps a system into a predetermined state. It installs software packages, starts or restarts services or puts configuration files in place and watches them for changes.

Having a state management system in place allows one to easily and reliably configure and manage a few servers or a few thousand servers. It allows configurations to be kept under version control.

Salt States is an extension of the Salt Modules that we discussed in the previous remote execution tutorial. Instead of calling one-off executions the state of a system can be easily defined and then enforced.

Understanding the Salt State System Components

The Salt state system is comprised of a number of components. As a user, an understanding of the SLS and renderer systems are needed. But as a developer, an understanding of Salt states and how to write the states is needed as well.

Note

States are compiled and executed only on minions that have been targeted. To execute functions directly on masters, see runners.

Salt SLS System

The primary system used by the Salt state system is the SLS system. SLS stands for SaLt State.

The Salt States are files which contain the information about how to configure Salt minions. The states are laid out in a directory tree and can be written in many different formats.

The contents of the files and they way they are laid out is intended to be as simple as possible while allowing for maximum flexibility. The files are laid out in states and contains information about how the minion needs to be configured.

SLS File Layout

SLS files are laid out in the Salt file server.

A simple layout can look like this:

top.sls
ssh.sls
sshd_config
users/init.sls
users/admin.sls
salt/master.sls
web/init.sls

The top.sls file is a key component. The top.sls files is used to determine which SLS files should be applied to which minions.

The rest of the files with the .sls extension in the above example are state files.

Files without a .sls extensions are seen by the Salt master as files that can be downloaded to a Salt minion.

States are translated into dot notation. For example, the ssh.sls file is seen as the ssh state and the users/admin.sls file is seen as the users.admin state.

Files named init.sls are translated to be the state name of the parent directory, so the web/init.sls file translates to the web state.

In Salt, everything is a file; there is no "magic translation" of files and file types. This means that a state file can be distributed to minions just like a plain text or binary file.

SLS Files

The Salt state files are simple sets of data. Since SLS files are just data they can be represented in a number of different ways.

The default format is YAML generated from a Jinja template. This allows for the states files to have all the language constructs of Python and the simplicity of YAML.

State files can then be complicated Jinja templates that translate down to YAML, or just plain and simple YAML files.

The State files are simply common data structures such as dictionaries and lists, constructed using a templating language such as YAML.

Here is an example of a Salt State:

vim:
  pkg.installed: []

salt:
  pkg.latest:
    - name: salt
  service.running:
    - names:
      - salt-master
      - salt-minion
    - require:
      - pkg: salt
    - watch:
      - file: /etc/salt/minion

/etc/salt/minion:
  file.managed:
    - source: salt://salt/minion
    - user: root
    - group: root
    - mode: 644
    - require:
      - pkg: salt

This short stanza will ensure that vim is installed, Salt is installed and up to date, the salt-master and salt-minion daemons are running and the Salt minion configuration file is in place. It will also ensure everything is deployed in the right order and that the Salt services are restarted when the watched file updated.

The Top File

The top file controls the mapping between minions and the states which should be applied to them.

The top file specifies which minions should have which SLS files applied and which environments they should draw those SLS files from.

The top file works by specifying environments on the top-level.

Each environment contains globs to match minions. Finally, each glob contains a list of lists of Salt states to apply to matching minions:

base:
  '*':
    - salt
    - users
    - users.admin
  'saltmaster.*':
    - match: pcre
    - salt.master

This above example uses the base environment which is built into the default Salt setup.

The base environment has two globs. First, the '*' glob contains a list of SLS files to apply to all minions.

The second glob contains a regular expression that will match all minions with an ID matching saltmaster.* and specifies that for those minions, the salt.master state should be applied.

Reloading Modules

Some Salt states require that specific packages be installed in order for the module to load. As an example the pip state module requires the pip package for proper name and version parsing.

In most of the common cases, Salt is clever enough to transparently reload the modules. For example, if you install a package, Salt reloads modules because some other module or state might require just that package which was installed.

On some edge-cases salt might need to be told to reload the modules. Consider the following state file which we'll call pep8.sls:

python-pip:
  cmd.run:
    - name: |
        easy_install --script-dir=/usr/bin -U pip
    - cwd: /

pep8:
  pip.installed:
    - require:
      - cmd: python-pip

The above example installs pip using easy_install from setuptools and installs pep8 using pip, which, as told earlier, requires pip to be installed system-wide. Let's execute this state:

salt-call state.apply pep8

The execution output would be something like:

----------
    State: - pip
    Name:      pep8
    Function:  installed
        Result:    False
        Comment:   State pip.installed found in sls pep8 is unavailable

        Changes:

Summary
------------
Succeeded: 1
Failed:    1
------------
Total:     2

If we executed the state again the output would be:

----------
    State: - pip
    Name:      pep8
    Function:  installed
        Result:    True
        Comment:   Package was successfully installed
        Changes:   pep8==1.4.6: Installed

Summary
------------
Succeeded: 2
Failed:    0
------------
Total:     2

Since we installed pip using cmd, Salt has no way to know that a system-wide package was installed.

On the second execution, since the required pip package was installed, the state executed correctly.

Note

Salt does not reload modules on every state run because doing so would greatly slow down state execution.

So how do we solve this edge-case? reload_modules!

reload_modules is a boolean option recognized by salt on all available states which forces salt to reload its modules once a given state finishes.

The modified state file would now be:

python-pip:
  cmd.run:
    - name: |
        easy_install --script-dir=/usr/bin -U pip
    - cwd: /
    - reload_modules: true

pep8:
  pip.installed:
    - require:
      - cmd: python-pip

Let's run it, once:

salt-call state.apply pep8

The output is:

----------
    State: - pip
    Name:      pep8
    Function:  installed
        Result:    True
        Comment:   Package was successfully installed
        Changes:   pep8==1.4.6: Installed

Summary
------------
Succeeded: 2
Failed:    0
------------
Total:     2

Generated on November 28, 2016 at 06:44:15 MST.

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