Ansible 和基于 `stdout` 值的 `changed_when`

问题描述

我正在运行一个自定义命令，因为我还没有找到一个可以做我需要的工作模块，我想调整 changed 标志以反映实际行为:

I am running a custom command because I haven't found a working module doing what I need, and I want to adjust the changed flag to reflect the actual behaviour:

- name: Remove unused images
  shell: '[ -n "$(docker images -q -f dangling=true)" ] && docker rmi $(docker images -q -f dangling=true) || echo Ignoring failure...'
  register: command_result
  changed_when: "command_result.stdout == 'Ignoring failure...'"

- debug: var="1 {{ command_result.stdout }}"
  when: "command_result.stdout != 'Ignoring failure...'"
- debug: var="2 {{ command_result.stdout }}"
  when: "command_result.stdout == 'Ignoring failure...'"

(我知道 shell 命令很难看，可以通过更复杂的脚本进行改进，但我现在不想这样做)

(I know the shell command is ugly and could be improved by a more complex script but I don't want to for now)

在无法删除 Docker 映像的主机上运行此任务会产生以下输出:

Running this task on an host where no Docker image can be removed gives the following output:

TASK: [utils.dockercleaner | Remove unused images] **************************** 
changed: [cloud-host] => {"changed": true, "cmd": "[ -n \"$(docker images -q -f dangling=true)\" ] && docker rmi $(docker images -q -f dangling=true) || echo Ignoring failure...", "delta": "0:00:00.064451", "end": "2015-07-30 18:37:25.620135", "rc": 0, "start": "2015-07-30 18:37:25.555684", "stderr": "", "stdout": "Ignoring failure...", "stdout_lines": ["Ignoring failure..."], "warnings": []}

TASK: [utils.dockercleaner | debug var="DIFFERENT {{ command_result.stdout }}"] *** 
skipping: [cloud-host]

TASK: [utils.dockercleaner | debug var="EQUAL {{ command_result.stdout }}"] *** 
ok: [cloud-host] => {
    "var": {
        "EQUAL Ignoring failure...": "EQUAL Ignoring failure..."
    }
}

所以，我有这个 stdout 返回值 "stdout": "Ignoring failure..."，并且调试任务显示字符串相等，所以 为什么任务仍然显示如改变"?

So, I have this stdout return value "stdout": "Ignoring failure...", and the debug task shows the strings are equal, so why is the task still displayed as "changed"?

我使用的是 ansible 1.9.1.

我指的文档是这个:http://docs.ansible.com/ansible/playbooks_error_handling.html#overriding-the-changed-result

推荐答案

我想你可能误解了 changed_when 的作用.

I think you may have misinterpreted what changed_when does.

changed_when 根据条件语句的评估将任务标记为已更改，在您的情况下为:

changed_when marks the task as changed based on the evaluation of the conditional statement which in your case is:

"command_result.stdout == '忽略失败...'"

所以只要这个条件为真，任务就会被标记为已更改.

So whenever this condition is true, the task will be marked as changed.

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