setting up a master slave configuration on ec2, lineinfile currently failing

gistfile1.txt

#!/usr/bin/env ansible-playbook
# Borrowed heavily from:
# https://github.com/64BitsPerMinute/ansible-elasticsearch-ec2-example/blob/master/deploy_elasticsearch.yml
---
- name: Provision the system modeler grid
  hosts: localhost
  gather_facts: False
  connection: local
  vars:
    ec2_access_key: '{{ nimbis_wolfram_aws_access_key }}'
    ec2_secret_key: '{{ nimbis_wolfram_aws_secret_key }}'
    keypair: wolfram
    region: us-east-1
    head_ami: ami-71772518
    head_count: 1
    head_group: system-modeler-head
    head_tag: system-modeler-head
    head_type: c1.medium
    worker_ami: ami-71772518
    worker_count: 3
    worker_group: system-modeler-grid
    worker_tag: system-modeler-worker
    worker_type: t1.micro

  tasks:

    - name: Launch worker instances
      ec2: >
        ec2_access_key={{ ec2_access_key }}
        ec2_secret_key={{ ec2_secret_key }}
        count={{ worker_count }}
        group={{ worker_group }}
        image={{ worker_ami }}
        instance_type={{ worker_type }}
        keypair={{ keypair }}
        region={{ region }}
        wait=yes
      register: workers

    - name: Launch head instance
      ec2: >
        ec2_access_key={{ ec2_access_key }}
        ec2_secret_key={{ ec2_secret_key }}
        count=1
        group={{ head_group }}
        image={{ head_ami }}
        instance_type={{ head_type }}
        keypair={{ keypair }}
        region={{ region }}
        wait=yes
      register: heads

    - name: Tag worker instances
      ec2_tag: >
        ec2_access_key={{ ec2_access_key }}
        ec2_secret_key={{ ec2_secret_key }}
        region={{ region }}
        resource={{ item.id }}
        state=present
      with_items: workers.instances
      args:
        tags:
            Name: '{{ worker_tag }}'
            GridMathematica: True
            SystemModeler: True
            Ansible: True

    - name: Tag head instance
      ec2_tag: >
        ec2_access_key={{ ec2_access_key }}
        ec2_secret_key={{ ec2_secret_key }}
        region={{ region }}
        resource={{ item.id }}
        state=present
      with_items: heads.instances
      args:
        tags:
            Name: '{{ head_tag }}'
            GridMathematica: True
            SystemModeler: True
            Ansible: True

    - name: Add workers to worker_hosts group
      add_host: >
        groups=worker_hosts
        name={{ item.public_dns_name }}
        private_dns_name={{ item.private_dns_name }}
      with_items: workers.instances

    - name: Add head to head_hosts group
      add_host: >
        groups=head_hosts
        name={{ item.public_dns_name }}
        ec2={{ item }}
      with_items: heads.instances

    - name: Wait for SSH to be available
      wait_for: >
        host={{ item.public_dns_name }} port=22
      with_items: workers.instances + heads.instances

- name: setup worker host file on head host
  hosts: head_hosts
  sudo: True

  tasks:
    - name: create a host file on the login nodes
      lineinfile: >
        dest=/etc/grid
        line={{ item.private_dns_name }}
      with_items: groups.worker_hosts