Getting familiar with the Ansible framework

In this section, you will understand how the Ansible framework fits into IT operations automation. We will explain how to start Ansible for the first time. Once you understand this framework, you will be ready to start learning more advanced concepts, such as creating and running playbooks with your own inventory.

In order to run Ansible's ad hoc commands via an SSH connection from your Ansible control machine to multiple remote hosts, you need to ensure you have the latest Ansible version installed on the control host. Use the following command to confirm the latest Ansible version:

$ ansible --version
ansible 2.9.6
 config file = /etc/ansible/ansible.cfg
 configured module search path = [u'/home/jamesf_local/.ansible/plugins/modules', u'/usr/share/ansible/plugins/modules']
 ansible python module location = /usr/lib/python2.7/dist-packages/ansible
 executable location = /usr/bin/ansible
 python version = 2.7.17 (default, Nov 7 2019, 10:07:09) [GCC 9.2.1 20191008]

You also need to ensure SSH connectivity with each remote host that you will define in the inventory. You can use a simple, manual SSH connection on each of your remote hosts to test the connectivity, as Ansible will make use of SSH during all remote Linux-based automation tasks:

$ ssh <username>@frontend.example.com
The authenticity of host 'frontend.example.com (192.168.1.52)' can't be established.
ED25519 key fingerprint is SHA256:hU+saFERGFDERW453tasdFPAkpVws.
Are you sure you want to continue connecting (yes/no)? yes
password:<Input_Your_Password>

In this section, we will walk you through how Ansible works, starting with some simple connectivity testing. You can learn how the Ansible framework accesses multiple host machines to execute your tasks by following this simple procedure:

1. Create or edit your default inventory file, /etc/ansible/hosts (you can also specify the path with your own inventory file by passing options such as –-inventory=/path/inventory_file). Add some example hosts to your inventory—these must be the IP addresses or hostnames of real machines for Ansible to test against. The following are examples from my network, but you need to substitute these for your own devices. Add one hostname (or IP address) per line:

frontend.example.com
backend1.example.com
backend2.example.com

$ ping frontend.example.com
PING frontend.example.com (192.168.1.52): 56 data bytes
64 bytes from 192.168.1.52: icmp_seq=0 ttl=64 time=0.040 ms
64 bytes from 192.168.1.52: icmp_seq=1 ttl=64 time=0.115 ms
64 bytes from 192.168.1.52: icmp_seq=2 ttl=64 time=0.097 ms
64 bytes from 192.168.1.52: icmp_seq=3 ttl=64 time=0.130 ms 

2. To make the automation process seamless, we'll generate an SSH authentication key pair so that we don't have to type in a password every time we want to run a playbook. If you do not already have an SSH key pair, you can generate one using the following command:

$ ssh-keygen 

When you run the ssh-keygen tool, you will see an output similar to the following. Note that you should leave the passphrase variable blank when prompted; otherwise, you will need to enter a passphrase every time you want to run an Ansible task, which removes the convenience of authenticating with SSH keys:

$ ssh-keygen 
Generating public/private rsa key pair.
Enter file in which to save the key (/Users/doh/.ssh/id_rsa): <Enter>
Enter passphrase (empty for no passphrase): <Press Enter>
Enter same passphrase again: <Press Enter>
Your identification has been saved in /Users/doh/.ssh/id_rsa.
Your public key has been saved in /Users/doh/.ssh/id_rsa.pub.
The key fingerprint is:
SHA256:1IF0KMMTVAMEQF62kTwcG59okGZLiMmi4Ae/BGBT+24 doh@danieloh.com
The key's randomart image is:
+---[RSA 2048]----+
|=*=*BB==+oo |
|B=*+*B=.o+ . |
|=+=o=.o+. . |
|...=. . |
| o .. S |
| .. |
| E |
| . |
| |
+----[SHA256]-----+

3. Although there are conditions that your SSH keys are automatically picked up with, it is recommended that you make use of ssh-agent as this allows you to load multiple keys to authenticate against a variety of targets. This will be very useful to you in the future, even if it isn't right now. Start ssh-agent and add your new authentication key, as follows (note that you will need to do this for every shell that you open):

$ ssh-agent bash
$ ssh-add ~/.ssh/id_rsa

$  ssh-copy-id -i ~/.ssh/id_rsa.pub frontend.example.com
/usr/bin/ssh-copy-id: INFO: Source of key(s) to be installed: "~/.ssh/id_rsa.pub"
/usr/bin/ssh-copy-id: INFO: attempting to log in with the new key(s), to filter out any that are already installed
/usr/bin/ssh-copy-id: INFO: 1 key(s) remain to be installed -- if you are prompted now it is to install the new keys
doh@frontend.example.com's password:

Number of key(s) added: 1

Now try logging into the machine, with: "ssh 'frontend.example.com'"
and check to make sure that only the key(s) you wanted were added.

$ ansible all -i hosts -m ping
frontend.example.com | SUCCESS => {
    "changed": false, 
    "ping": "pong"
}
backend1.example.com | SUCCESS => {
    "changed": false, 
    "ping": "pong"
}
backend2.example.com | SUCCESS => {
    "changed": false, 
    "ping": "pong"
}

backend2.example.com | FAILED => SSH encountered an unknown error during the connection. We recommend you re-run the command using -vvvv, which will enable SSH debugging output to help diagnose the issue