The article gives an overview of the fundamental ideas behind the Salt platform, along with setup and usage examples and comments.
What it is?
Built on a dynamic communication bus, Salt is an open source platform for managing infrastructure. Salt may be used to alter data, conduct commands remotely, manage settings for any collection of systems or applications, and more.
Our instructions explain how to install Salt Master and Salt Minions on servers running the Ubuntu 18.04 operating system, as well as how to set up their communication.
Masters и Minions
Requests to remotely execute instructions are transmitted to the Salt Master (Master), a server that serves as a command and control hub for its minions. For instance, this command displays the current disk utilization for each of the slaves under the master’s control:
salt '*' disk.usage
There are many such teams. For example, you can install NGINX on a minion named webserver1:
salt 'webserver1' pkg.install nginx
Salt Minions (Nodes, Minions) – these are your servers under the control of the master, it is on them that applications and services are launched. Each minion is assigned an ID, and the master can refer to this ID to assign commands to specific minions.
Communication between the master and minions is carried out using the ZeroMQ transport protocol , the channel is encrypted with a pair of public and private keys. The key pair is generated by the minion, after which it sends its public key to the master.
Remote execution
Salt offers a very wide range of modules for remote command execution. The runtime module is a set of related functions that you can run on minions on command from the master. For example:
salt 'webserver1' npm.install gulp
In this command, npm is the module and install is the function. This command installs the Gulp Node.js package through the Node Package Manager (NPM).
The available runtime modules are convenient solutions for system administration:
- creation and management of system users
- installing and uninstalling software
- editing or creating configuration files
The cmd.run function is used to run arbitrary commands on managed minions:
salt '*' cmd.run 'ls -l /etc'
This command will list the contents of the /etc directory for each minion.
States, Formulas, and Top File
Salt offers another way to manage a node, which is to describe the state in which the minion should be. This kind of configuration is called Salt state (state), and the methodology is usually called configuration management.
States are defined in state files. After the minion states are described, they are applied to the minion.
Status Description
The following is an example of a state file /srv/salt/webserver_setup.sls that ensures that the following components are installed: rsync, curl, NGINX, and that NGINX is started and enabled when the OS boots:
network_utilities:
pkg.installed:
- pkgs:
- rsync
- curl
nginx_pkg:
pkg.installed:
- name: nginx
nginx_service:
service.running:
- name: nginx
- enable: True
- require:
- pkg: nginx_pkg
The.sls (SaLt State) extension is used to signify state files. State descriptions, which are top-level sections and include network utilities, nginx pkg, and nginx service in the example above, can be found in one or more state files. Because description IDs are completely random, you may give them whatever name you choose.
State modules are contained in state descriptions. Although they are distinct from execution modules, state modules frequently carry out identical functions. For instance, the pkg execution module’s pkg.installed status function and pkg.install execution function may be found in the pkg status module.
State files are simply collections of dictionaries, lists, strings, and numbers that Salt then interprets. By default, Salt uses YAML syntax to represent states.
State files are usually stored on the Salt master’s file system, but they can also be stored elsewhere on the file server, such as a Git repository.
Applying State to a Minion
To apply a state to a minion, use the state.apply function on behalf of the master:
salt `webserver1` state.apply webserver_setup
This command applies the sample state webserver_setup.sls to a minion named webserver1. When applying the state, the .sls suffix is not mentioned. All state descriptions from the state file are applied.
Formulas
Formulas are only collections of states that when combined, configure a system or application component on a minion. Formulas are often laid down in a variety of ways. files sls. It may be simpler to manage your work if you separate formula states into various files. Declarations in other files may be referred to and included in state declarations.
Top file
In addition to manually applying states to minions, Salt provides the ability to automatically display which states should be applied to different minions. This is called the top file.
A simple example of the /srv/salt/top.sls file:
base:
'*':
- universal_setup
'webserver1':
- webserver_setup
base is the environment. You can specify more than one environment corresponding to different phases of your work; for example: development, QA, production.
The example above says that the universal_setup state should apply to all minions (‘*’), while the webserver_setup state should only apply to the webserver1 minion.
If you run the state.apply function with no arguments, Salt will check the top file and apply all the states in it according to the generated mapping:
salt '*' state.apply
Storage of Data (data) and Secrets (secrets)
A Pillar function in the Salt framework distributes specific data from the master to the minions. Pillar is mostly used to store sensitive information like credentials. If you don’t want to write non-secret information directly to state files, Pillar is a useful location to keep it.
Let’s imagine you want to give each of your minions a unique skin by creating system users for them. This data might be encoded into a state file, but it would necessitate a new declaration for every user. You just need to build one state declaration and add the data to it if you store the data in Pillar instead.
Such data is stored in .sls files, such as the /srv/pillar/user_info.sls file:
users:
joe:
shell: /bin/zsh
amy:
shell: /bin/bash
sam
shell: /bin/fish
As with state files, the Top file (separate from the Yop state file) maps Pillar data to minions, like /srv/pillar/top.sls:
base:
'webserver1':
- user_info
The template is Jinja
To use Pillar data in state files, Jinja templates are used .
The following is an example of a /srv/salt/user_setup.sls state file that uses the Pillar data from the previous section to create system users and set up a shell:
{% for user_name, user_info in pillar['users'].iteritems() %} {{ user_name }}: user.present: - shell: {{ user_info['shell'] }} {% endfor %}
Salt will compile the state file into a similar file before applying it to the minion:
joe:
user.present:
- shell: /bin/zsh
amy:
user.present:
- shell: /bin/bash
sam:
user.present:
- shell: /bin/fish
In the following example, the state file /srv/salt/webserver_setup.sls will install Apache and set the name for the package to match the operating system:
install_apache:
pkg.installed:
{% if grains['os'] == 'CentOS' %}
- name: httpd
{% else %}
- name: apache
{% endif %}
More information can be found in the official product documentation .
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