Ansible Tutorial for Network Engineers – Cisco Router Configuration Backup

In this Cisco Ansible tutorial for beginners I will take you from the very beginning, installing Ansible on Ubuntu, to setting up the folders and running through a simple playbook which will backup the configuration of a Cisco router. I will say that I am not a Linux expert so if you notice any Linux errors or better ways of doing things please comment and I will update this article.

What is Ansible?

Ansible is a free-software platform for configuring and managing computers or network devices which combines multi-node software deployment, ad hoc task execution, and configuration management. (description taken from wikipedia)

It can also be used for network management. The beauty of Ansible is that it is does not require an agent on the host system it uses SSH for transport. As long as Ansible can make an SSH connection to the target device you are good to go. Ansible used to be primarily used for server administration but in the last few years more and more network modules have been added to the software and Ansible is a skill that all Network Engineers should be getting up to speed on.

There are two versions, free and paid. The paid version is called Ansbile Tower and will not be described here.

This Ansible tutorial will cover the free version installed on an Ubuntu desktop.

Ansible Tutorial Step 1 – How to Install Ansible on Ubuntu

You can install Ansible on many versions of Linux but for this tutorial I will using Ubuntu 16.04 LTS running within VMWorkstation Pro

For my lab I am running this on on my laptop. I will run 2 VMs, the first is Ubuntu Desktop to run Ansible and the other will be a Cisco CSR1000V router.

From this point on I am assuming that you have a clean version of Ubuntu installed.

There will be a few enhancements I make to Ubuntu to make running Ansible easier which will be detailed along the way.

Installing Ansible

Before we start lets just establish that Ansible is not already installed on this system.
You can do this with the ansible –version command

roger@ubuntu:~$ ansible --version
The program 'ansible' is currently not installed. You can install it by typing:
sudo apt install ansible

The best way to get Ansible for Ubuntu is to add the project’s PPA (personal package archive) to your system.

Open a terminal and run the command:

sudo apt-get update

Then run the command

sudo apt-get install software-properties-common

Now the package is installed you can install Ansible by entering the following command.

sudo apt-add-repository ppa:ansible/ansible

You will need to press ENTER to accept the PPA addition.

Next run the command

sudo apt-get update

Finally to install Ansible run the command

sudo apt-get install ansible

Ansible is now installed and can be verified with the command

ansible --version

At the time of writing the current Ansible version is 2.2.1.0

roger@ubuntu:~$ ansible --version
ansible 2.2.1.0
  config file = /etc/ansible/ansible.cfg
  configured module search path = Default w/o overrides
roger@ubuntu:~$

Ok so now we have Ansible installed lets start using it.

Enable Colorful Terminal in Debian and Ubuntu

One of the extras I have enable in my Ubuntu install is the colorful terminal as shown below

To get the coloured prompt you need to edit the file .bashrc

This process is described here 

Start using Ansible

The first thing to do is to drop into the Ansible folder and explore the default folder structure.

From your home prompt run the command

cd /etc/ansible

then issue a dir and let’s see whats in there

In the default Ansible installation there are two files and a directory

ansible.cfg contains all the default values and the main ones are listed below

# some basic default values...

#inventory = /etc/ansible/hosts
#library = /usr/share/my_modules/
#remote_tmp = ~/.ansible/tmp
#local_tmp = ~/.ansible/tmp
#forks = 5
#poll_interval = 15
#sudo_user = root
#ask_sudo_pass = True
#ask_pass = True
#transport = smart
#remote_port = 22
#module_lang = C
#module_set_locale = False

For this tutorial we are not going to touch the Ansible.cfg file but you just need to be aware of it’s location.

For this tutorial we just need to be aware that the default inventory file location is /etc/ansible/hosts

This file defines all the hosts you will be connecting to – so let’s look at that file.

From within the Ansible directory lets edit the hosts file

vi hosts

You can see all hosts in the default file are commented out

For our backup Cisco Router playbook we just need to add one router in there so I am going to add a group called CSR-Routers and add one router.

My hosts files now looks like this

# Ex 2: A collection of hosts belonging to the CSR-Routers' group
[CSR-Routers]
CSR-01 ansible_host=192.168.244.129

You can enter names of devices in here if your Ubuntu host can resolve them in DNS but for this basic tutorial I am just using the ansible_host command

I can now reference this host in one of two ways. Either by calling CSR-Routers or CSR-01. If I call CSR-Routers my playbook will action on every device within the CSR-Routers group if I call CSR-01 in my playbook then it will only action on that single device.

What is an Ansible Playbook?

Before we go any further I just need to define one term that you will be using every day whilst working with Ansible and that is a playbook. In simple terms a playbook is a file formatted in YAML

YAML stands for YAML Ain’t Markup Language but is also referred to as Yet Another Markup Language. Basically YAML is a very readable code that defines all the actions and tasks that your playbook will perform. Let’s look at the finished playbook below to backup a cisco router and go through each line step by step in a very quick Ansible playbook tutorial.

Ansible Playbook to Backup Cisco Router

My playbook is called backup_cisco_router.yaml

 
---
- hosts: CSR-01
  gather_facts: true
  connection: local

  tasks:
   - name: show run 
   ios_command:
   commands:
     - show run 
     host: "{{ ansible_host }}"
     username: roger
     password: KanKu009
     register: config

  - name: save output to /etc/ansible/backups 
  copy: 
  content: "{{ config.stdout[0] }}"
  dest: "/etc/ansible/backups/show_run_{{ inventory_hostname }}.txt"

I have this saved in a folder called playbooks /etc/ansible/playbooks

I have also created a folder called backups in /etc/ansible/backups

Let’s step through each line

— the first line of any YAML file has to start with three dashes – this denotes it as a YAML file

– hosts: CSR-01 the next line starts with a single dash and defines the hosts that this playbook should run agains, in this case our single CSR router

gather_facts: true this line needs to be here to define we are collecting information

connection: local this defines the connection will be made from this box

tasks: we now start to define the actual task that will run

– name: show run – this is the name of our first task

ios_command: this is an ansible module and is some code within the Ansible core that can be used to run commands in ios – more info here

commands: what follows here is the command that will be run

– show run in our case show run

host: “{{ ansible_host }}” this defines the connection variables for the ansible host – username / password etc

username: local username defined on the router

password: local password defined on the router

register: config Once Ansible has connected to the router and run the show run command it registers that information to a variable called config (you can call this what you want)

-name save output to /etc/ansible/backups – this is the name of the next task and is just a description

copy: this is calling another Ansible Module called copy

content: “{{ config.stdout[0] }}” this registers the config to a format called stdout

dest: “/etc/ansibe/backups/show_run_{{ inventory_hostname }}.txt” – this defines the destination and filename format which will be show_run_hostname.txt

Running the Ansible Playbook

So we now have an Ansible playbook written, we have defined a host and we now need to run the playbook.

I have a CSR1000v router running so lets see what happens

To run an Ansible Playbook you run the command

ansible-playbook <playbook name>

so in our case

ansible-playbook backup_cisco_router.yaml

You can see the descriptions of each task and if the play was successful.

Conclusion

So we have successfully created an Ansible Playbook that will backup a single Cisco router, you can hopefully see that this could easily be scaled out to perform this task on 100’s or 1000’s of devices and also to run other commands like sh ip int brief, sh log, sh ip ospf neighbor etc.

Ansible is a very powerful tool and is going to change the way network engineers work in the future.

I hope you enjoyed this simple tutorial and there will be more to come.