"Idempotent" ec2 creation with ansible

ec2-instance__tasks__main.yml

---
- name: Find trusty ami for base image
  ec2_ami_search:
    distro: ubuntu
    release: trusty
    region: "{{ aws_region }}"
    store: ebs-ssd
    virt: hvm
  register: ubuntu
  when: not aws_ami_id is defined

- name: Use a custom ami
  set_fact:
    current_ami: "{{ aws_ami_id }}"
  when: aws_ami_id is defined

- name: Use the base ubuntu ami
  set_fact:
    current_ami: "{{ ubuntu.ami }}"
  when: not aws_ami_id is defined

- name: Determine random private subnet
  set_fact:
    current_subnet: "{{ item }}"
  with_random_choice: aws_private_subnets

- name: Query for existing instance
  command: aws ec2 describe-instances --region {{ aws_region }} --filter Name=tag:Name,Values={{ hostname }} --query "Reservations[].Instances[].PrivateIpAddress" --output text
  register: query_private_ip

- name: Create an ec2 instance if none exists
  ec2:
    count: "{{ aws_instance_count }}"
    group_id: "{{ aws_default_sg }}"
    key_name: wm-infrastructure
    image: "{{ current_ami }}"
    instance_type: "{{ aws_instance_type }}"
    instance_tags:
      Name: "{{ hostname }}"
      Purpose: "{{ purpose }}"
      Requestor: "{{ requestor | default('') }}"
    region: "{{ aws_region }}"
    vpc_subnet_id: "{{ current_subnet }}"
    wait: yes
  when: query_private_ip.stdout == ''

- name: Get ip address of existing or created instance
  command: aws ec2 describe-instances --region {{ aws_region }} --filter Name=tag:Name,Values={{ hostname }} --query "Reservations[].Instances[].PrivateIpAddress" --output text
  register: query_private_ip

- name: Set fact for ip address
  set_fact:
    ec2_instance_private_address: "{{ query_private_ip.stdout }}"

- name: Add instance to group for later plays
  add_host:
    name: "{{ ec2_instance_private_address }}"
    groups: to_be_provisioned

- name: Wait for ssh to respond
  wait_for:
    host: "{{ ec2_instance_private_address }}"
    port: 22

playbook.yml

---
- hosts: localhost
  gather_facts: yes
  sudo: no
  roles:
  - ec2-instance

- hosts: to_be_provisioned
  gather_facts: yes
  sudo: no
  tasks:
  - name: Debug
    debug:
      msg: "{{ ec2_id }}"