Why I cannot prompt for a variable that will be shared by multiple plays (ansible 1.6.5)

Question

I have distilled a playbook that has three plays. The goal is to collect the database password from a prompt in one play and then use the same password in the other two plays.

---

- name: database password
  hosts:
    - webservers
    - dbservers
  vars_prompt:
    - name: "db_password"
      prompt: "Enter Database Password for databse user root"
      default: "root"

- hosts: dbservers
  tasks:
    - command: echo {{db_password | mandatory }}


- hosts: webservers
  tasks:
    - command: echo {{db_password | mandatory }}

It fails as shown below.

Enter Database Password for databse user root [root]: 

PLAY [database password] ****************************************************** 

GATHERING FACTS *************************************************************** 
ok: [vc-dev-1]

PLAY [dbservers] ************************************************************** 

GATHERING FACTS *************************************************************** 
ok: [vc-dev-1]

TASK: [command echo {{db_password | mandatory}}] *************************** 
fatal: [vc-dev-1] => One or more undefined variables: 'db_password' is undefined

FATAL: all hosts have already failed -- aborting

PLAY RECAP ******************************************************************** 
           to retry, use: --limit @.../playbook2.retry

vc-dev-1                   : ok=3    changed=0    unreachable=1    failed=0   

Answer 1

I have found the following workaround using set_fact to assign the variable entered by a user into a variable with playbook scope. It seems that var_prompt variables are not like facts and other variables, its scope is restricted in the play that prompts for them not the entire playbook. I am not sure if this is a feature or a bug.

---

- name: database password
  hosts:
    - webservers
    - dbservers
  vars_prompt:
    - name: "db_password"
      prompt: "Enter Database Password for databse user root"
      default: "root"
  tasks:
    - set_fact:
        db_root_password: "{{db_password}}"

- hosts: dbservers
  tasks:
    - command: echo {{db_root_password | mandatory }}


- hosts: webservers
  tasks:
    - command: echo {{db_root_password | mandatory }}

Answer 2

Improvising gae123's answer, in case if your hosts are added dynamically, it will not be possible to get and set the fact on the existing group of servers, in which case localhost can be used to set and get.

---
- name: database password
  hosts: localhost
  vars_prompt:
    - name: "db_password"
      prompt: "Enter Database Password for databse user root"
      default: "root"
  tasks:
    - set_fact:
        db_root_password: "{{db_password}}"

- hosts: dbservers
  vars:
    - db_root_password: "{{ hostvars['localhost']['db_root_password'] }}"
  tasks:
    - command: echo {{db_root_password | mandatory }}


- hosts: webservers
  vars:
    - db_root_password: "{{ hostvars['localhost']['db_root_password'] }}"
  tasks:
    - command: echo {{db_root_password | mandatory }}