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Ansible 定义变量与条件判断


2019-04-23 by dongnan

目标

使用 ansible 判断目标服务器 /etc/hosts 文件是否存在指定的主机名,不存在则添加该主机名。

操作步骤

定义 playbook

cat copy_docker-config.yml

---
- hosts: node
  remote_user: root

  tasks:
    - name: copy docker directory
      copy:
        src: "/root/.docker"
        dest: "/root/"
        owner: root
        group: root
        directory_mode: 0700

    - name: 1 - update /etc/hosts
      shell: grep 'hub.demo.com' /etc/hosts || echo 404
      register: host_name

    - name: 2 - update /etc/hosts
      shell: echo "172.16.100.111 hub.demo.com" >> /etc/hosts
      when: host_name.stdout == '404'

执行 playbook

ansible-playbook copy_docker-config.yml -v

Using /etc/ansible/ansible.cfg as config file
# ...省略

TASK [copy
 docker directory]
**********************************************************************************************************************************************
changed:
 [node3] => {"changed": true, "checksum":
"ab9e360b0374992885df5556232ac87c3192d4c5", "dest":
"/root/.docker/config.json", "gid": 0, "group": "root", "md5sum":
"8c6250f01bcaf61747b6922b98561a1b", "mode": "0644", "owner": "root",
"size": 165, "src":
"/root/.ansible/tmp/ansible-tmp-1555666013.67-8330150906498/source",
"state": "file", "uid": 0}
# ...省略

TASK [1 - update /etc/hosts]
**********************************************************************************************************************************************
changed:
 [node3] => {"changed": true, "cmd": "grep 'hub.demo.com' /etc/hosts
|| echo 404", "delta": "0:00:00.020902", "end": "2019-04-19
17:26:54.661432", "rc": 0, "start": "2019-04-19 17:26:54.640530",
"stderr": "", "stderr_lines": [], "stdout": "404", "stdout_lines":
["404"]}
# ...省略

TASK [2 - update /etc/hosts]
**********************************************************************************************************************************************
skipping: [node1] => {"changed": false, "skip_reason": "Conditional result was False"}
# ...省略
changed:
 [node3] => {"changed": true, "cmd": "echo \"172.16.100.111
hub.demo.com\" >> /etc/hosts", "delta": "0:00:00.019457", "end":
"2019-04-19 17:26:54.935612", "rc": 0, "start": "2019-04-19
17:26:54.916155", "stderr": "", "stderr_lines": [], "stdout": "",
"stdout_lines": []}

PLAY RECAP
**********************************************************************************************************************************************
node1                      : ok=3    changed=1    unreachable=0    failed=0  
node2                      : ok=3    changed=2    unreachable=0    failed=0  
node3                      : ok=4    changed=3    unreachable=0    failed=0     

结果

  • node1 与 node2 的 /etc/hosts 文件包含 hub.demo.com 这个域名跳过了后续的命令。
  • node3 /etc/hosts 不含此域名,则执行 echo shell 命令。

小结

  • register 语句注册变量,存储某个命令的输出结果在变量中,方便后续使用。例如 host_name变量的值是 grep命令的输出结果。
  • when 语句做条件判断,When语句包含Jinja2表达式,例如 host_name.stdout == '404' 条件True则执行上面的 shell 命令,False则跳过。
  • 其中 host_name 变量是类似 python字典,例如 {"stdout": "172.16.100.111"}host_name.stdout 则获得其value 。

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参考

ansible 条件选择

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