Managing Linux server configs with the SaltStack

Managing Linux server configs with the SaltStack

I came across Salt while searching for an alternative to Puppet. I like puppet, but I am falling in love with Salt :). This maybe a personal opinion but I found Salt easier to configure and get started with as compared to Puppet. Another reason I like Salt is that it let’s you manage your server configurations from the command line, for example:

To update all your servers with Salt, just run

salt ‘*’ pkg.upgrade

Installing the SaltStack on Linux.

Salt is available in the EPEL repo if you are installing it on CentOS 6/7, Pi and Ubuntu linux users can add the Salt Repository from here. Since Salt is python based you can also use ‘pip’ to install it but you have take care of dependencies like yum-utils and other packages yourself.

Salt follows the Server-Client model, The Server is known as the master whereas clients are called minions.

Installation and Configuration of a Salt Master

[root@salt-master~]# yum install salt-master

Salt configurations files are stored in /etc/salt and /srv/salt. Salt is good to go out of the box, but I would recommend you configure a bit more verbose logging to help your troubleshoot.

[root@salt-master ~]# vim /etc/salt/master
#Default is warning change to the following
log_level: debug
log_level_logfile: debug

[root@salt-master ~]# systemctl start salt-master

Installation and Configuration of a Salt minion

[root@salt-minion~]#yum install salt-minion

#Add the hostname of your Salt Master
[root@salt-minion~]#vim /etc/salt/minion
master: salt-master.com
#start the minion
[root@salt-minion~] systemctl start salt-minion

On Startup, a minion will generate a cryptographic key and an id. It will then connect to the Salt Master and identify itself. The Salt Master must accept the minion’s key before allowing the minion to download a configuration.

Listing and Accepting keys on the Salt Master

#List all keys
[root@salt-master~] salt-key -L
Accepted Keys:
Unaccepted Keys:
minion.com
Rejected Keys:

#Accept key with id ‘minion.com’
[root@salt-master~]salt-key -a minion.com

[root@salt-master~] salt-key -L
Accepted Keys:
minion.com
Unaccepted Keys:
Rejected Keys:

Once you have accepted a minions keys, you can get information on it immediately using the ‘salt’ command.

Salt command line examples

#Check if a minion is up and running
[root@salt-master~]  salt 'minion.com' test.ping
minion.com:
    True
# run shell commands on the minion
 [root@salt-master~]#  salt 'minion.com' cmd.run 'ls -l'
minion.com:
    total 2988
    -rw-r--r--. 1 root root 1024 Jul 31 08:24 1g.img
    -rw-------. 1 root root     940 Jul 14 15:04 anaconda-ks.cfg
    -rw-r--r--. 1 root root 1024  Aug 14 17:21 test
#install/update a software on all your servers
[root@salt-master ~]# salt '*' pkg.install git

The salt command needs a few components to send information. One of these components is the minion id and another is the function to be called on the minion.
In the first example I used the ‘ping’ function of the ‘test’ module to check if the system is up. This function does not perform an actual ping, it just return’s ‘true’ if the minion responds.
‘cmd.run’ is used to execute remote commands and ‘pkg’ module contains functions for package management. The full list of builin modules is at the end of this post.

Grains example
Salt uses an interface called Grains to get system information. You can use grains to run commands on systems with particular properties.

[root@vps4544 ~]# salt -G 'os:Centos' test.ping
minion:
    True

More grain examples are available at http://docs.saltstack.com/en/latest/topics/targeting/grains.html

Package Management via the State File System.
In order to automate software configurations you will need to use the state system and create a state file. These files use the YAML format and python dictionaries, lists, strings and numbers for data structure. Reading up on them will help you understand the configurations better.

VIM state file example

[root@salt-master~]# vim /srv/salt/vim.sls
vim-enhanced:
  pkg.installed
/etc/vimrc:
  file.managed:
    - source: salt://vimrc
    - user: root
    - group: root
    - mode: 644
  

The first and third line in this file are called state id. They must contain the exact name or path of the package or file to be managed. After the state ids are state and function declaration. ‘pkg’ and file are state declarations whereas ‘installed’ and ‘managed’ are function declarations. Functions accept arguments, user,group,mode and source are all arguments to the function ‘managed’.

To apply this configuration to a minion move your ‘vimrc’ file to ‘/srv/salt’ and run.

[root@salt-master~]# salt 'minion.com' state.sls vim
minion.com:
----------
          ID: vim-enhanced
    Function: pkg.installed
      Result: True
     Comment: The following packages were installed/updated: vim-enhanced.
     Started: 09:36:23.438571
    Duration: 94045.954 ms
     Changes:
              ----------
              vim-enhanced:
                  ----------
                  new:
                      7.4.160-1.el7
                  old:


Summary
------------
Succeeded: 1 (changed=1)
Failed:    0
------------
Total states run:     1

You can also add dependencies to your configurations.

[root@salt-master~]# vim /srv/salt/ssh.sls
openssh-server:
  pkg.installed


/etc/ssh/sshd_config:
  file.managed:
    - user: root
    - group: root
    - mode: 600
    - source: salt://ssh/sshd_config

sshd:
  service.running:
    - require:
      - pkg: openssh-server

The ‘require’ statement here is a requisite declaration, it creates a dependency between the ‘service’ and ‘pkg’ states. This declaration will first check if the package is installed and then run the service.

However, I prefer using the ‘watch’ statement as it also checks for file modifications and restarts the service.

[root@salt-master~]# vim /srv/salt/ssh.sls
openssh-server:
  pkg.installed


/etc/ssh/sshd_config:
  file.managed:
    - user: root
    - group: root
    - mode: 600
    - source: salt://sshd_config

sshd:
  service.running:
    - watch:
      - pkg: openssh-server
      - file: /etc/ssh/sshd_config

[root@vps4544 ssh]# salt 'minion.com' state.sls ssh
seven.leog.in:
     Changes:
----------
          ID: openssh-server
    Function: pkg.installed
      Result: True
     Comment: Package openssh-server is already installed.
     Started: 13:01:55.824367
    Duration: 1.156 ms
     Changes:
----------
          ID: /etc/ssh/sshd_config
    Function: file.managed
      Result: True
     Comment: File /etc/ssh/sshd_config updated
     Started: 13:01:55.825731
    Duration: 334.539 ms
     Changes:
              ----------
              diff:
                  ---
                  +++
                  @@ -14,7 +14,7 @@
                   # SELinux about this change.
                   # semanage port -a -t ssh_port_t -p tcp #PORTNUMBER
                   #
                  -Port 22
                  +Port 422
                   #AddressFamily any
                   #ListenAddress 0.0.0.0
                   #ListenAddress ::

----------
          ID: sshd
    Function: service.running
      Result: True
     Comment: Service restarted
     Started: 13:01:56.473121
    Duration: 407.214 ms
     Changes:
              ----------
              sshd:
                  True

Summary
------------
Succeeded: 4 (changed=2)
Failed:    0
------------
Total states run:     4

Maintaining all config files in single directory can make scaling a complex task, hence you can create sub-directories and add your configuration in them with a init.sls file

[root@salt-master~]# mkdir /srv/salt/ssh
[root@salt-master~]# vim /srv/salt/ssh/init.sls
openssh-server:
  pkg.installed


/etc/ssh/sshd_config:
  file.managed:
    - user: root
    - group: root
    - mode: 600
    - source: salt://ssh/sshd_config

sshd:
  service.running:
    - watch:
      - pkg: openssh-server
      - file: /etc/ssh/sshd_config

[root@vps4544 ssh]# cp /etc/ssh/sshd_config /srv/salt/ssh/
[root@vps4544 ssh]# salt 'minion.com' state.sls ssh

Top File and Environments.
A Top file (top.sls) is where you define your environments. A top file allows you to map minions to packages. The default environment is ‘base’. You need to define which packages will be installed on which server under the base environment.
If there are multiple environments and more than one definitions for a particular minion is used then by default the base environment will supersede the others.

To define an environment you need to add it to the ‘file_roots’ directive in the master configuration file.

[root@salt-master ~]# vim /etc/salt/master
file_roots:
  base:
    - /srv/salt
  dev:
    - /srv/salt/dev

Now add a top.sls file in /srv/salt

[root@salt-master ~]# vim /srv/salt/top.sls
base:
  '*':
    - vim
  'minion.com':
     - ssh

Apply the top file configuration with

[root@salt-master~]# salt '*' state.highstate
minion.com:
----------
          ID: vim-enhanced
    Function: pkg.installed
      Result: True
     Comment: Package vim-enhanced is already installed.
     Started: 13:10:55
    Duration: 1678.779 ms
     Changes:
----------
          ID: openssh-server
    Function: pkg.installed
      Result: True
     Comment: Package openssh-server is already installed.
     Started: 13:10:55.
    Duration: 2.156 ms

The minion will download the top file and search for it’s configuration. It will also apply the configuration for all minions.

You can also Setup a Front end For Saltstack with Foreman.

This is just a brief introduction to Salt, for in depth understanding you can go through the links below and if you are already using Salt and have any recommendations do let me know.

Update : For a list of Linux CheatSheets, Guides and Tutorials checkout the DevOps Wiki at https://github.com/Leo-G/DevopsWiki

 

Read

http://docs.saltstack.com/en/latest/ref/states/top.html#how-top-files-are-compiled
http://docs.saltstack.com/en/latest/topics/tutorials/states_pt1.html
http://docs.saltstack.com/en/latest/ref/states/highstate.html#state-declaration

http://theforeman.org/plugins/foreman_salt/

Grains
http://docs.saltstack.com/en/latest/topics/targeting/grains.html

List of Salt Modules

Good comparison of Salt and puppet
https://mywushublog.com/2013/03/configuration-management-with-salt-stack/

Full list of builtin execution modules
http://docs.saltstack.com/en/latest/ref/modules/all/

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Leo G

Is a Linux Hobbyist and Enthusiast. He Strongly believes in OpenSource Software and would like you to view and download his software at https://github.com/Leo-g
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