当主机1在ansible中失败时如何使用组中的第二台主机？

Question

我有一个包含 500 多个组的清单，每个组有 2 个主机，1 个是主要的，另一个是次要的。在我的剧本中，我正在做两件事。一是获取无法访问的主机列表，二是在主服务器中执行命令。

我的库存示例：（就像这样，我有 500 多个来自 set1...set500 的组）

[set1]
host1set1 setup=primary
host2set1 setup=secondary
[set1:vars]
setidentifier=set1

我能够收集无法访问的主机列表并在主服务器中执行命令。 现在，我想知道只有当我的主服务器无法访问时，如何在辅助服务器中执行命令。

  - delegate_to: localhost
    command: ping -c1 "{{ hostvars[inventory_hostname].ansible_host|default(inventory_hostname) }}"
    register: ping
    ignore_errors: true
    become: false

  - set_fact:
     available: "{{ ping.rc == 0 }}"

  - lineinfile:
      dest: "/tmp/available.txt"
      line: "{{ hostvars[inventory_hostname]. }} : {{ inventory_hostname }}"
      regexp: "Host: {{ inventory_hostname }}"
      create: true
    delegate_to: localhost
    become: false
    when: "{{ hostvars[inventory_hostname].available }} == False"

  - shell: date
    register: dateout
    when: "setup is search('primary')"

只有当我的主服务器无法访问时，我才需要在辅助服务器中执行shell任务（我提到日期命令仅供参考，我还有其他事情要做。）。

有人可以在这里阐明一下我该怎么做吗？

Answer 1

仅在组中的单个主机上执行任务 - 尝试使用 run_once: true 执行 ansible 任务，详细参考 cab 可以找到 here

如果您知道 master 是可访问的，您可以为组中的剩余主机设置一个变量 fact（如 execute_on_secondary = False），并将其用于任务的block 中的 when 条件

- set_fact:
    execute_on_secondary: False
  delegate_to: "{{ item }}"
  with_items: "{{ play_hosts }}"
  run_once: yes
  when: ## condition for when primary is reachable ##

- block:
    # tasks here
  when: setup == "primary" or execute_on_secondary

---

下面的方法很简单。在业务关键系统上使用之前对其进行测试。

- hosts: all
  serial: 2
  tasks:
    - set_fact: ## same as above ##
      run_once: yes
    - block:
        # tasks here
      when: setup == "primary" or execute_on_secondary    

Answer 2

首先 Ping 组。无法访问的主机将被排除在未来的播放之外：

这是我的库存：

[groupA]
AnsibleTower ansible_host=192.168.124.8
[groupB]
jaxsat ansible_host=192.168.124.111
rhel7.5 ansible_host=192.168.124.4

现在，这是没有 ping 的剧本：

---
- hosts: groupB
  gather_facts: no
  connection: ssh
  tasks:
  - name: Run hostname command
    command: /bin/hostname
    register: result
    run_once: yes 

  - name: Show result
    debug:
      var: result
    run_once: yes 

因为jaxsat 关闭而失败：

$ ansible-playbook -i inventory/ test_one_only.yml

PLAY [groupB] **********************************************************************************

TASK [Run hostname command] ********************************************************************
Tuesday 21 July 2020  13:40:38 -0400 (0:00:00.064)       0:00:00.064 ********** 
fatal: [jaxsat]: UNREACHABLE! => {"changed": false, "msg": "Failed to connect to the host via ssh: ssh: connect to host 192.168.124.111 port 22: No route to host\r\n", "unreachable": true}
 [WARNING]: Failure using method (v2_runner_on_unreachable) in callback plugin
(<ansible.plugins.callback.mail.CallbackModule object at 0x7f95688fbf10>): [Errno 111]
Connection refused


NO MORE HOSTS LEFT *****************************************************************************
    to retry, use: --limit @/home/jack/Ansible/TEST/test_one_only.retry

PLAY RECAP *************************************************************************************
jaxsat                     : ok=0    changed=0    unreachable=1    failed=0   

Tuesday 21 July 2020  13:40:42 -0400 (0:00:03.218)       0:00:03.283 ********** 
=============================================================================== 
Run hostname command -------------------------------------------------------------------- 3.22s
Playbook run took 0 days, 0 hours, 0 minutes, 3 seconds

现在，我添加ping：

---
- hosts: groupB
  gather_facts: no
  connection: ssh
  tasks:
  - name: ping all hosts
    ping:

  - name: Run hostname command
    command: /bin/hostname
    register: result
    run_once: yes 

  - name: Show result
    debug:
      var: result
    run_once: yes 

并且jaxsat 没有在其他任务上尝试过：

$ ansible-playbook -i inventory/ test_one_only.yml

PLAY [groupB] **********************************************************************************

TASK [ping all hosts] **************************************************************************
Tuesday 21 July 2020  13:42:12 -0400 (0:00:00.057)       0:00:00.057 ********** 
ok: [rhel7.5]
fatal: [jaxsat]: UNREACHABLE! => {"changed": false, "msg": "Failed to connect to the host via ssh: ssh: connect to host 192.168.124.111 port 22: No route to host\r\n", "unreachable": true}
 [WARNING]: Failure using method (v2_runner_on_unreachable) in callback plugin
(<ansible.plugins.callback.mail.CallbackModule object at 0x7f07f21ad850>): [Errno 111]
Connection refused


TASK [Run hostname command] ********************************************************************
Tuesday 21 July 2020  13:42:15 -0400 (0:00:03.217)       0:00:03.275 ********** 
changed: [rhel7.5]

TASK [Show result] *****************************************************************************
Tuesday 21 July 2020  13:42:15 -0400 (0:00:00.348)       0:00:03.623 ********** 
ok: [rhel7.5] => {
    "result": {
        "changed": true, 
        "cmd": [
            "/bin/hostname"
        ], 
        "delta": "0:00:00.001530", 
        "end": "2020-07-21 13:42:15.921749", 
        "failed": false, 
        "rc": 0, 
        "start": "2020-07-21 13:42:15.920219", 
        "stderr": "", 
        "stderr_lines": [], 
        "stdout": "localhost.localdomain.localdomain", 
        "stdout_lines": [
            "localhost.localdomain.localdomain"
        ]
    }
}
    to retry, use: --limit @/home/jack/Ansible/TEST/test_one_only.retry

PLAY RECAP *************************************************************************************
jaxsat                     : ok=0    changed=0    unreachable=1    failed=0   
rhel7.5                    : ok=3    changed=1    unreachable=0    failed=0   

Tuesday 21 July 2020  13:42:15 -0400 (0:00:00.037)       0:00:03.661 ********** 
=============================================================================== 
ping all hosts -------------------------------------------------------------------------- 3.22s
Run hostname command -------------------------------------------------------------------- 0.35s
Show result ----------------------------------------------------------------------------- 0.04s
Playbook run took 0 days, 0 hours, 0 minutes, 3 seconds