Ansible

Ansible, the name of resounding legend.

Problem ?

There are many use cases like this where you would need to add a line to a file.

It could be as simple as adding a new host in the /etc/hosts of multiple servers to allow for DNS resolution using a particular IP.

It could also be about whitelisting an IP address (adding it to the whitelisting plain text file).

Adding a line to /etc/hosts

In this scenario, we want to add a line to the /etc/hosts file

Skip this part if you know the use of /etc/hosts

The /etc/hosts file is a plaintext-file on standard GNU/Linux OS.

Its purpose is to allow for DNS resolution of the host.

It has priority over DNS servers.

codax@gaming:~$ ping www.google.com
PING www.google.com (216.58.223.100) 56(84) bytes of data.
64 bytes from mba01s08-in-f4.1e100.net (216.58.223.100): icmp_seq=1 ttl=117 time=44.5 ms

Now, as we see, google is resolving with IP address 216.58.223.100

Say, I’m living in france and I want to resolve it to google.fr.

1. Then I need to check the IP of google.fr, just to see if it’s a different IP

    codax@gaming:~$ ping www.google.fr
    PING www.google.fr (216.58.223.99) 56(84) bytes of data.
    64 bytes from mba01s08-in-f3.1e100.net (216.58.223.99): icmp_seq=1 ttl=117 time=42.2 ms
   

2. I would add the following line in /etc/hosts in the format: IP[Space or tab]FQDN

    codax@gaming:~$ vim /etc/hosts
    codax@gaming:~$ tail -n3 /etc/hosts
    ff02::2 ip6-allrouters
    216.58.223.100 www.google.fr
   

   What i’m doing is forcing google.com to resolve to google.fr

3. Now when i type in: www.google.com, I’m redirected to google.fr transparently.

Changed on 1 server

OK, easy.

On multiple servers, we’ll use ansible.

# Playbook name: add_googlefr.yaml
hosts: MyFrontend
- name: Add google.fr to /etc/hosts
  lineinfile:
    path: /etc/hosts
    line: '216.58.223.100 www.google.fr'
    state: present
    backup: yes

Why use this method?

• It adds a line at the end of the text file

• It doesn’t create duplicates if line is present.

• Rollback: Remove the line by replacing the state: present with ‘absent’

Credits

Ansible logo

\Codarren/