Getting Started with Salt Stack-the Other Configuration Management System Built with Python

Configuration Management

If you haven't used any type of configuration management system before, here is a simple example. Say you have a set of configurations and packages that you generally install for every Web server. You can keep these configuration directives in small text files and then instruct your servers to install these packages and configure them to your liking, every time you create a new server. You also can use configuration management to keep all of your servers updated once they have been created and respond to changes in packaging or new configurations.

Let's install the libpam-cracklib package, so you can add additional requirements for user passwords. I chose this package because it is useful for almost any server connected to the Internet. It allows you to set additional password requirements regarding length, and it requires that your users' passwords contain special characters or numerals. You easily could substitute any particular package you want. These examples do require that the package be available in your system's package manager though.

Storage of the Configuration Directives

Salt's configuration management directives and files are, by default, kept within the /srv/salt directory. This is where all your configuration files and any files you want to copy to any of your minions reside. Salt also includes a file server system as part of the configuration management features. Salt doesn't touch your master's system files though, so don't worry; all configuration management takes place within the /srv/salt directory.

Salt, by default, uses PyYAML (http://pyyaml.org) syntax for its template files, but numerous other templating languages are available as well. Be sure to follow the proper formatting techniques for YAML, which involves two spaces instead of tabs. I have found the on-line YAML parser (http://yaml-online-parser.appspot.com) to be invaluable when troubleshooting syntax issues with YAML files.

Enable Configuration Management

To enable the configuration management functionality within Salt, you need to edit your master configuration file once again. In /etc/salt, open your master file and locate the lines that refer to file_roots. In the default configuration, this was around line 156. Now, uncomment this directive by removing the # from the following lines:

file_roots:
  base:
    - /srv/salt

This tells Salt where to locate your configuration management files. Depending on how you installed Salt, you may need to create the /srv/salt directory.

Create a Top File or "Roadmap"

The base configuration file is known as a Top File, and it resides within the /srv/salt directory. Let's create one now. This file provides mappings for other files and can be used to set a base configuration for all servers. Again, with your favorite text editor, create a top.sls file within the /srv/salt directory. You can think of this file as a roadmap for different directions for each minion. Within your top.sls file, add the following lines:

base:
  '*'
    - servers

The base directive lets Salt know that this configuration is a base configuration and can be applied to all machines. The wild-card '*' targets every machine. The - servers directive is an arbitrary name that allows you to recognize what the directive pertains to. Feel free to choose something that makes sense to you. This entry also refers to a particular configuration file that you will now create to install the libpam-cracklib.

Create a Server-Specific Configuration File

After you save your top.sls file, create a new file called servers.sls within the /srv/salt directory. This file will hold your specific configuration, including the name of the package to be installed and also a reference to a configuration file. In the new servers.sls file, add the following:

libpam-cracklib:
  pkg:
    - installed

The first line is the name of the package specifically how your package manager refers to it. For example, the Apache HTTP server is called apache2 in aptitude-based package manager distributions, but httpd in yum-based package management systems. Make sure you use the proper name for the package depending on which package manager you are using. You can target specific package names using what Salt refers to as grains. Refer to the documentation for more information and advanced examples of using grains in SLS files to target distribution-specific systems (http://salt.readthedocs.org/en/latest/topics/tutorials/states_pt3.html#using-grains-in-sls-modules).

Lines 2 and 3 tell Salt what to do with this package. For this example, you want it installed. To remove a package, you simply would change - installed to - removed. Remember, spacing is very important! On line two, there are two spaces before pkg:, and on the third line, there are four spaces before - installed. If you receive any errors, check your syntax via an on-line YAML parser.