Ansible lineinfile give an error with /etc/hosts - provisioning

Question

I have this simple task in my role:
- name: Updating the /etc/hosts
lineinfile: dest=/etc/hosts line="192.168.99.100 {{ item }}"
with_items:
- domain1.com
- domain2.com
tags: etc
When I run my Ansible playbook:
robe:ansible-develop robe$ ansible-playbook -i inventory develop-env.yml -vvvv --extra-vars "user=`whoami`" --tags etc --become-user=robe --ask-become-pass
SUDO password:
PLAY [127.0.0.1] **************************************************************
GATHERING FACTS ***************************************************************
<127.0.0.1> REMOTE_MODULE setup
<127.0.0.1> EXEC ['/bin/sh', '-c', 'mkdir -p /tmp/ansible-tmp-1446050161.27-256837595805154 && chmod a+rx /tmp/ansible-tmp-1446050161.27-256837595805154 && echo /tmp/ansible-tmp-1446050161.27-256837595805154']
<127.0.0.1> PUT /var/folders/x1/dyrdksh50tj0z2szv3zx_9rc0000gq/T/tmpMYjnXz TO /tmp/ansible-tmp-1446050161.27-256837595805154/setup
<127.0.0.1> EXEC ['/bin/sh', '-c', 'chmod a+r /tmp/ansible-tmp-1446050161.27-256837595805154/setup']
<127.0.0.1> EXEC /bin/sh -c 'sudo -k && sudo -H -S -p "[sudo via ansible, key=rqphpqfpcbsifqtnwflmmlmpwrcnkpqe] password: " -u robe /bin/sh -c '"'"'echo BECOME-SUCCESS-rqphpqfpcbsifqtnwflmmlmpwrcnkpqe; LANG=en_US.UTF-8 LC_CTYPE=en_US.UTF-8 /usr/bin/python /tmp/ansible-tmp-1446050161.27-256837595805154/setup'"'"''
<127.0.0.1> EXEC ['/bin/sh', '-c', 'rm -rf /tmp/ansible-tmp-1446050161.27-256837595805154/ >/dev/null 2>&1']
ok: [127.0.0.1]
TASK: [docker-tool-box | Updating the /etc/hosts] *****************************
<127.0.0.1> REMOTE_MODULE lineinfile dest=/etc/hosts line="192.168.99.100 ptxrt.com"
<127.0.0.1> EXEC ['/bin/sh', '-c', 'mkdir -p /tmp/ansible-tmp-1446050161.49-9492873099893 && chmod a+rx /tmp/ansible-tmp-1446050161.49-9492873099893 && echo /tmp/ansible-tmp-1446050161.49-9492873099893']
<127.0.0.1> PUT /var/folders/x1/dyrdksh50tj0z2szv3zx_9rc0000gq/T/tmpyLOGd6 TO /tmp/ansible-tmp-1446050161.49-9492873099893/lineinfile
<127.0.0.1> EXEC ['/bin/sh', '-c', u'chmod a+r /tmp/ansible-tmp-1446050161.49-9492873099893/lineinfile']
<127.0.0.1> EXEC /bin/sh -c 'sudo -k && sudo -H -S -p "[sudo via ansible, key=nofwziqxytbhjwhluhtzdfcqclqjuypv] password: " -u robe /bin/sh -c '"'"'echo BECOME-SUCCESS-nofwziqxytbhjwhluhtzdfcqclqjuypv; LANG=en_US.UTF-8 LC_CTYPE=en_US.UTF-8 /usr/bin/python /tmp/ansible-tmp-1446050161.49-9492873099893/lineinfile'"'"''
<127.0.0.1> EXEC ['/bin/sh', '-c', 'rm -rf /tmp/ansible-tmp-1446050161.49-9492873099893/ >/dev/null 2>&1']
failed: [127.0.0.1] => (item=ptxrt.com) => {"failed": true, "item": "ptxrt.com"}
msg: The destination directory (/private/etc) is not writable by the current user.
FATAL: all hosts have already failed -- aborting
PLAY RECAP ********************************************************************
to retry, use: --limit #/Users/robe/develop-env.retry
127.0.0.1 : ok=1 changed=0 unreachable=0 failed=1
I don't understand why the error msg said:
msg: The destination directory (/private/etc) is not writable by the current user.
The correct directory should be /etc/hosts.
Any clue?
I am working on MacOS.
My playbook is:
- hosts: 127.0.0.1
connection: local
become: yes
become_method: sudo
become_user: "{{user}}"
roles:
- role-1
- role-2
I put the become_user by command line. So all my roles are running with become. And it still doesn't work.

Answer 1

On OSX the /etc/ folder is actually a symlink to the /private/etc/ folder - hence the error. (Ansible is just transparently following the symlink).
As for the error you're going to need to run the task with become: yes (sudo permissions) to be able to write to /etc/hosts/
Edit based on update and commments
To get the correct privileges to edit the hosts file you need to be root. Setting become: yes on the task is good enough for this for OSX as Ansible will default to sudo as the become method and root as the user.
To specify the sudo password you can do one of two things.
Use --ask-become-pass on the command line and Ansible will prompt you when it needs it
Use the ansible_become_pass variable on the group or host in the inventory file. E.g. localhost ansible_become_pass=batman
Note that the Ansible docs recommend against 2 and using 1 so as not to store your password in plain text.