来自vars_prompt的主机的ansible变量中不再接受

Question

我已将ansible升级到v2.6.2。升级后，不再接受来自vars_prompt的主机的ansible变量。

---
- hosts: "{{ hosts }}"
  vars_prompt:
    - name: "hosts"
      private: no

  tasks:
  - name: touch file
    command: touch /home/tomcat/a

我遇到了错误

ERROR! The field 'hosts' has an invalid value, which includes an undefined variable. The error was: 'hosts' is undefined

The error appears to have been in '/home/tomcat/test.yml': line 2, column 3, but may
be elsewhere in the file depending on the exact syntax problem.

The offending line appears to be:

---
- hosts: "{{ hosts }}"
  ^ here
We could be wrong, but this one looks like it might be an issue with
missing quotes.  Always quote template expression brackets when they
start a value. For instance:

    with_items:
      - {{ foo }}

Should be written as:

    with_items:
      - "{{ foo }}"

对此有何建议？