Ansible Playbook Variable Prompt Not Working [duplicate] - ansible

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 }}

Answer 3

I ended up taking user3037143 answer for my localhost sudo password problem:
---
- hosts: localhost
tags:
- always
vars_prompt:
- name: sudo_password
prompt: "Sudo password for localhost ONLY"
tasks:
- set_fact: ansible_become_password={{ sudo_password }}
no_log: true
Now it's shared between every include playbooks I have.
I'm on ansible > 2.