How to get IP address from controller's /etc/hosts file?

[Robert F]

I'm trying to get the IP address of one of my remote hosts by querying my controller machine's /etc/hosts file which happens to contain the IP addresses of all the servers I build with Ansible.  My Ansible playbook looks like this:

---
hosts: all
gather_facts: yes
become: yes


pre_tasks:
  - name: get file server's IP address
    command: "grep prod-fs1 /etc/hosts | awk '{ print $0 }'"
    register: fs_ip_addr
    delegate_to: localhost


  - debug: var={{ fs_ip_addr }}

However, I'm getting this error which I don't know how to fix:

TASK [get file server's IP address] *************************************************************************************************************************************************
fatal: [prod-web1.example.com -> localhost]: FAILED! => {"changed": true, "cmd": ["grep", "prod-fs1", "/etc/hosts", "|", "awk", "{ print $0 }"], "delta": "0:00:00.010303", "end": "2020-03-03 12:24:36.207656", "msg": "non-zero return code", "rc": 2, "start": "2020-03-03 12:24:36.197353", "stderr": "grep: |: No such file or directory\ngrep: awk: No such file or directory\ngrep: { print $0 }: No such file or directory", "stderr_lines": ["grep: |: No such file or directory", "grep: awk: No such file or directory", "grep: { print $0 }: No such file or directory"], "stdout": "/etc/hosts:45.79.93.135    prod-fs1.example.com    prod-fs1", "stdout_lines": ["/etc/hosts:45.79.93.135    prod-fs1.example.com    prod-fs1"]}


PLAY RECAP **************************************************************************************************************************************************************************
prod-web1.example.com : ok=7    changed=0    unreachable=0    failed=1    skipped=0    rescued=0    ignored=0;p

It appears that the error is caused by the pipe symbol which is why I enclosed the entire command in double quotes.  But the error occurs even if I remove them.

I should add that I know I could use this method of getting the IP address of my file server...

   - name: get file server's IP address
     set_fact: fs_ip_addr=hostvars[groups['fileservers'][0]]['ansible_eth0']['ipv4']['address']

However, this option isn't available to me since I have to call the playbook with the "limit" argument which cause the variable to not be available.

deploy-webservers.yml -I inventory -l webservers

[Robert F]

Note that my awk command should say "print $1" to get the IP address.  I don't see a way to edit my original question here to make this change.

[Jean-Yves LENHOF]

Hi,

Not read everything but first thing is that if you have a pipe in a command call.... you should use shell module instead... That should fix your first issue.

Regards,

JYL

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[Juerg Ritter]

Hi Robert,

Try using the shell module instead of the command module. The command module doesn't execute a command in a shell, hence you cannot use shell functionality such as a pipes and redirections.

Hope that helps!

--Juerg

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[Robert F]

I neglected to mention that I did try the shell and it did not fix the problem.  But thanks for the suggestion!

[Dick Visser]

Hii

If you

1. Properly format your playbook to be a list of plays

2. Use shell

3. Don't use {{ }} around the var in your debug task

Then it works:

TASK [get file server's IP address] ****************************************************************

changed: [villa -> localhost]

TASK [debug] ***************************************************************************************
ok: [villa] =>
  fs_ip_addr:
    changed: true
    cmd: grep prod-fs1 /etc/hosts | awk '{ print $0 }'
    delta: '0:00:00.008973'
    end: '2020-03-04 00:36:05.873228'
    failed: false
    rc: 0
    start: '2020-03-04 00:36:05.864255'
    stderr: ''
    stderr_lines: []
    stdout: 10.10.10.20 prod-fs1
    stdout_lines:
    - 10.10.10.20 prod-fs1

But I would also recommend:

4. Dropping privilege escalation for local actions

5. Use "print $1" as this will match the actual IP

6. Use 'stdout' sa this will be the actual IP

Thus the playbook would be:

---
- hosts: all

  gather_facts: yes
  become: yes

  pre_tasks:
    - name: get file server's IP address

      shell: "grep prod-fs1 /etc/hosts | awk '{ print $1 }'"
      register: fs_ip_addr
      become: no
      delegate_to: localhost

    - debug: var=fs_ip_addr.stdout

And then output would be:

TASK [debug] ***********************************************************************************************
ok: [villa] =>
  fs_ip_addr.stdout: 10.10.10.20

Although shell+grep+awk still sounds fragile

Dick

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Dick Visser
Trust & Identity Service Operations Manager
GÉANT

[Robert F]

Dick,

Thank you very much!  Your solution worked.  I realized after I posted my question that I should have said "print $1" but I didn't see a way to edit my question.  I had also forgotten that when you do "debug: var=..." that you have to drop the double braces; they're only used when you do "debug: msg=...".  Removing privilege escalation and using stdout were new to me.  Thanks again.