Ansible任务中向vars传入字典报错问题排查

我使用Ansible [core 2.16.6]编写了如下代码，通过set_fact生成字典类型变量pgs_server_custom_role_vars，debug验证其为字典且内容正确，但在import_role的vars字段传入该变量时，却报错提示“Vars in a IncludeRole must be specified as a dictionary”。请问这是Bug还是操作有误？

代码示例 #

- name: Install and configure PGS servers for RZ
  hosts: pgs_rzdb_servers
  tasks:
    - name: Prepare pgs_server role variables
      set_fact:
        pgs_server_custom_role_vars: >-
          {{ 
            {
              'pgs_server_version': pgs_rzdb_server_version,
              'pgs_server_port': pgs_rzdb_server_port,
              'pgs_server_pg_hba_rules': pgs_rzdb_server_pg_hba_rules,
              'pgs_server_max_connections': pgs_rzdb_server_max_connections,
              'pgs_server_idle_in_transaction_session_timeout': pgs_rzdb_server_idle_in_transaction_session_timeout,
              'pgs_server_marker': 'RZDB'
            }
            | dict2items
            | selectattr('value', 'defined')
            | items2dict
          }}

    - debug:
        msg: "Role variables: {{ pgs_server_custom_role_vars }}"

    - debug:
        msg: "Role variables: {{ pgs_server_custom_role_vars | type_debug }}"

    - name: pgs_server
      import_role:
        name: pgs_server
      vars: "{{ pgs_server_custom_role_vars }}"
      tags:
        - pgs_server

Debug输出 #

TASK [debug] ************************************************************************************************************************************************************************************************************************************** ok: [lspostgres02.ls.local] => { "msg": "Role variables: {'ls_pgs_server_version': 13, 'ls_pgs_server_port': 5431, 'ls_pgs_server_pg_hba_rules': [{'contype': 'host', 'users': 'all', 'source': 'lxserver.ls.local', 'databases': 'all', 'method': 'md5'}, {'contype': 'host', 'users': 'all', 'source': '192.168.69.0/24', 'databases': 'all', 'method': 'md5'}], 'ls_pgs_server_marker': 'RZDB'}" }

TASK [debug] ************************************************************************************************************************************************************************************************************************************** ok: [lspostgres02.ls.local] => { "msg": "Role variables: dict" }

报错信息 #

ERROR! Vars in a IncludeRole must be specified as a dictionary

The error appears to be in '/mnt/c/Users/dhe/Documents/Checkouts/ls-ansible/ls_pgs_rzdb_servers.yml': line 30, column 13, but may
be elsewhere in the file depending on the exact syntax problem.

The offending line appears to be:

        name: pgs_server
      vars: "{{ pgs_server_custom_role_vars }}"
            ^ 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 }}"

问题分析与解决 #

这不是Bug，是操作有误，核心原因是**import_role与set_fact的执行时机不匹配**：

根本原因 #

import_role属于Ansible的静态导入模块，会在playbook解析阶段就处理所有参数（包括vars字段）；而set_fact是在playbook运行阶段才会创建变量pgs_server_custom_role_vars。

也就是说，当Ansible解析import_role的vars参数时，目标变量还未被生成，此时Ansible无法识别出它是字典类型，因此抛出错误。而debug任务是运行阶段执行的，此时变量已经存在，所以能正常显示内容。

解决方法 #

有两种可行的修复方案：

方案1：改用动态导入的include_role

include_role是运行阶段处理的模块，能正确获取到set_fact生成的变量，修改后的代码如下：

- name: pgs_server
  include_role:
    name: pgs_server
  vars: "{{ pgs_server_custom_role_vars }}"
  tags:
    - pgs_server

方案2：提前在解析阶段定义变量

如果必须使用import_role，可以把变量生成逻辑移到play的vars部分（解析阶段处理），确保import_role能在解析时获取到变量：

- name: Install and configure PGS servers for RZ
  hosts: pgs_rzdb_servers
  vars:
    pgs_server_custom_role_vars: >-
      {{ 
        {
          'pgs_server_version': pgs_rzdb_server_version,
          'pgs_server_port': pgs_rzdb_server_port,
          'pgs_server_pg_hba_rules': pgs_rzdb_server_pg_hba_rules,
          'pgs_server_max_connections': pgs_rzdb_server_max_connections,
          'pgs_server_idle_in_transaction_session_timeout': pgs_rzdb_server_idle_in_transaction_session_timeout,
          'pgs_server_marker': 'RZDB'
        }
        | dict2items
        | selectattr('value', 'defined')
        | items2dict
      }}
  tasks:
    - debug:
        msg: "Role variables: {{ pgs_server_custom_role_vars }}"

    - debug:
        msg: "Role variables: {{ pgs_server_custom_role_vars | type_debug }}"

    - name: pgs_server
      import_role:
        name: pgs_server
      vars: "{{ pgs_server_custom_role_vars }}"
      tags:
        - pgs_server

内容的提问来源于stack exchange，提问作者henkesde92