Salting your LXC Container Fleet

Saltstack is an awesome configuration management system that can make managing 10 to 10,000 servers very simple. Salt can be used to deploy, manage, configure, report around, and even troubleshoot all of your servers. It can also be used to manage a fleet of LXC containers which we will be doing in this blog post. If you have been reading this blog, you know that I love Linux Containers. I am using them for pretty much anything these days. Salt is a great way to keep track of and manage all of these containers. On my main server, I have three containers that are running various applications. In order to update the packages on these containers I would have to log into each one, and run apt-get update and apt-get upgrade. This is not so bad for three containers, but you can imagine how annoying and cumbersome this gets as your container lists grows. This is where salt comes to the rescue, with salt I can update all of these containers with a single command. The official Salt Walkthrough is a great place to start to learn about how Salt works. This short post will show you how to set up a small salt configuration on a single server that is hosting several containers. All of my containers are pretty boring because they run Ubuntu 14.04. The best part about salt is that it is really OS agnostic and can manage a diverse fleet of different versions and types of operating systems. For this post, my host and all of my LXC containers are running Ubuntu 14.04 LTS Salt works by having a master that manages a bunch of minions. Setting up salt master is a breeze. For the purpose of this blog post, we refer to the master as being your host server and the minions as being your LXC containers.

Setting up Salt Master

sudo add-apt-repository ppa:saltstack/salt

sudo apt-get update 
sudo apt-get install salt-master

Setting up your Firewall

# Allow Minions from these networks 
-I INPUT -s 10.0.3.0/24 -p tcp -m multiport --dports 4505,4506 -j ACCEPT  

  Allow Salt to communicate with Master on the loopback interface
  
    
  

-A INPUT -i lo -p tcp -m multiport –dports 4505,4506 -j ACCEPT

  Reject everything else
  
    
  

-A INPUT -p tcp -m multiport –dports 4505,4506 -j REJECT

sudo iptables-restore < /etc/iptables.firewall.rules

Setting up your Minions

screen -dRR container1 lxc-attach -n container1

sudo apt-get install software-properties-common  
sudo add-apt-repository ppa:saltstack/salt  
sudo apt-get update  
sudo apt-get install salt-minion

vim /etc/hosts  # Now add the master IP  10.0.3.1    salt

/etc/init.d/salt-minion start

salt '*' test.ping

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