Get started with Ansible

Ansible is a configuration management tools, in the same space as Puppet, Chef, Cfengine, SaltStack and few others. For so long being a developer and also wearing a sysadmin hat, I have try to avoid using any of these configuration management software, thinking they just added unnecessary complexity to your workflow. But after spending countles hours building automation script backed by Makefiles, bash, python with fabric, I started to value a dedicated tools for these tasks.

The easiest way to get latest version of Ansible is by using python tools PIP. Begin by installing it using apt-get (Ubuntu 12.04):-

sudo apt-get install python-pip
sudo pip install ansible

Inventory

The first concept to understand in Ansible is the Inventory, a plain text file where we keep list of hosts (servers) we want to manage. By default ansible will look at /etc/ansible/hosts. The content of the file should look like this:-

cat /etc/ansible/hosts
[server1]
192.168.0.1:10022

[server2]
192.168.0.2:10022

The format can be more complex but above is enough for us to get started.
Basically we define the server name and below it's hostname, either IP address or DNS name such as server1.com. By default ansible will connect using standard ssh port 22 but if your ssh running on different port, use the format hostname:port. The server name actually act as group so you can have more than 1 host in each action. Following also possible:-

[web-servers]
web1.server.com
web2.server.com

[db-servers]
192.168.0.1

Now we can run our first ansible command:-

ansible server1 -a '/bin/ls'
192.168.0.1 | success | rc=0 >>
dir1
dir2

The above simply run command ls on the remote server and print it output.
This by no means useful enough or better than just plain ssh with command but think about running the command on few servers at the same time. The above command also bring us to next concept in ansible - Module.

Credentials

The above command will work only if you already setup password-less authentication to your server using ssh public key. Otherwise you have to tell ansible to use username/password authentication instead. For this you need sshpass to be installed:-

sudo apt-get install sshpass

Then re-run previous ansible command by passing the extra options:-

ansible server1 -a '/bin/ls' -u yourname -k
SSH password:

The option -k will prompt you to enter the password. If you already set up SSH key but not using the default private, you can specify it through the command line:-

ansible server1 -a '/bin/ls' -u yourname --private-key /path/to/id_rsa-custom

Module

Module basically what defined the ansible functionality. There are modules to run command (like above), add/remove user, install packages, copy files, provision new virtual machine instance such as AWS EC2 or Digital Ocean droplets and much more.

Through the command line, we can specify what module to run using -m option and the arguments that the module require through -a option, like we're doing above. If we don't specify -m, the default would be command. So both commands below are equivalent:-

ansible server1 -a '/bin/ls'
ansible server1 -m command -a '/bin/ls'

Playbook

Playbook is what really make ansible a configuration management software. It allow us to declaratively define what command to execute in order to configure our system. It use YAML for the file format. Let's try a very simple example, define a playbook that create new user, setup ssh key and then install nginx webserver:-

- hosts: server1
  tasks:
    - name: Add main user
      user: name=kamal
            home=/home/kamal

    - name: Set up authorized key for kamal
      authorized_key: user=kamal
                      state=present
                      key="{{ item }}"
      with_file:
        - /home/kamal/.ssh/id_rsa-do.pub

    - name: Upgrade apt packages
      apt: upgrade=yes
           update_cache=yes

    - name: Install common packages
      apt: pkg={{ item }}
      with_items:
        - build-essential
        - telnet

    - name: Install nginx
      apt: name=nginx

    - name: Start nginx
      command: service nginx start

Save the above playbook as main.yml and then we can execute it through command:-

ansible-playbook main.yml -u root -i ansible_hosts.ini -k

That's all for now. I'll try to post more topics on ansible as I progress through my way learning it up.

Notes

<10.0.3.125> ESTABLISH CONNECTION FOR USER: ubuntu
fatal: [10.0.3.125] => to use the 'ssh' connection type with passwords, you 
must install the sshpass program

On minimal ubuntu installation, some required packages maybe not installed:-

TASK: [Upgrade apt packages] ************************************************** 
failed: [10.0.3.125] => {"failed": true}
msg: Could not import python modules: apt, apt_pkg. Please install python-apt 
package.

We need at least python-apt and aptitude to be pre-installed on the remote system.