Use ansible to insert into etc hosts file

Question

I want to insert the following entry into the /etc/hosts file somehow using Ansible.

10.33.5.44 ip-10-33-5-44

Here, the schema is that the ip should have an alias corresponding to the IP, prefixed with ip- and where the dot . would be replaced by dash -.

But to get this IP, I can only think of doing the host command on a DNS name e.g.

host euwest2-test-box.company.com
> euwest2-test-box.company.com has address 10.33.5.44

Can anyone suggest how to get that to work? Is it possible?

So you just want in your host to make an alias prefixing the ip with ip- ? — β.εηοιτ.βε
– β.εηοιτ.βε, Commented Jul 13, 2020 at 8:38

β.εηοιτ.βε · Accepted Answer · 2020-07-13 10:00:07Z

7

You can use the dig lookup in order to achieve this. Then add the lines in the hosts file with lineinefile.

Please mind that the module dig needs the Python library dnspython to operate. So you might want to install it as well with Ansible.

So, given the playbook:

- hosts: all
  gather_facts: no
  
  tasks:
    - package:
        name: py-dnspython
        state: present
    - lineinfile:
        path: /etc/hosts
        line: "{{ item }} ip-{{ item | replace('.', '-') }}"
      loop: "{{ lookup('dig', 'stackoverflow.com.').split(',') }}"

This gives the recap:

PLAY [all] *********************************************************************************************

TASK [package] *****************************************************************************************
changed: [localhost]

TASK [lineinfile] **************************************************************************************
changed: [localhost] => (item=151.101.1.69)
changed: [localhost] => (item=151.101.65.69)
changed: [localhost] => (item=151.101.129.69)
changed: [localhost] => (item=151.101.193.69)

PLAY RECAP *********************************************************************************************
localhost                  : ok=2    changed=2    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

And populate the hosts file accordingly:

127.0.0.1   localhost
::1 localhost ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
172.17.0.3  21eef8264e0c
151.101.1.69 ip-151-101-1-69
151.101.65.69 ip-151-101-65-69
151.101.129.69 ip-151-101-129-69
151.101.193.69 ip-151-101-193-69

edited Jul 13, 2020 at 10:00

answered Jul 13, 2020 at 9:53

β.εηοιτ.βε

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6 Comments

Saffik Over a year ago

Great stuff, I do however get a permission denied error. I tried using become: true but that didn't work either. Any ideas? - See: justpaste.it/6qxot

β.εηοιτ.βε Over a year ago

You need to become the root user indeed on this very first package task, if you are not already

β.εηοιτ.βε Over a year ago

Maybe you have an upper level become_user set to another user? If so, you'll need to add both become: true and become_user: root in the package task.

Saffik Over a year ago

Right, added that. Also... is there any way to append a command to it. I wanted to run it inside a conda environment because I have conda running. When I install dnspython and then run your solution... it complains that there is no package called dnspython.

Saffik Over a year ago

I tried but didn't work: loop: "source /home/ubuntu/anaconda3/bin/activate myCondaEnv {{ lookup('dig', 'stackoverflow.com.').split(',') }}"

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