Ansible任务控制loop循环、when和block条件判断介绍演示


[root@main playkongzhi]# cat loop1.yaml 
---
- hosts: servera
  tasks:
    - name: test item
      debug: 
        msg: "{{ item }}"
      loop:
        - 'a'
        - 'b'
        - 'c'
        
[root@main playkongzhi]# ansible-playbook loop1.yaml
ok: [servera] => (item=a) => {
    "msg": "a"
}
ok: [servera] => (item=b) => {
    "msg": "b"
}
ok: [servera] => (item=c) => {
    "msg": "c"
}

（2）遍历输出以变量定义的webservers组内主机


[root@main playkongzhi]# cat loop1.yaml 
---
- hosts: servera
  tasks:
    - name: test item
      debug: 
        msg: "{{ item }}"
      loop: "{{ groups.webservers }}"
      
[root@main playkongzhi]# ansible-playbook loop1.yaml
ok: [servera] => (item=servera) => {
    "msg": "servera"
}
ok: [servera] => (item=serverb) => {
    "msg": "serverb"
}

（3）遍历输出以字典定义的数据

循环输出hello和nihao


[root@main playkongzhi]# cat loop1.yaml 
---
- hosts: servera
  tasks:
    - name: test item
      debug: 
        msg: "{{ item }}"
      loop:
        - x1: 'hello'
        - x2: 'nihao'
[root@main playkongzhi]# ansible-playbook loop1.yaml
ok: [servera] => (item={u'x1': u'hello'}) => {
    "msg": {
        "x1": "hello"
    }
}
ok: [servera] => (item={u'x2': u'nihao'}) => {
    "msg": {
        "x2": "nihao"
    }
}

（4）遍历嵌套定义的loop

循环创建user1和user2


[root@main playkongzhi]# cat loopuser.yaml 
---
- hosts: servera
  tasks:
    - name: create user1 and user2
      user:
        name: "{{ item.name }}"
        state: present
        uid: "{{ item.uid }}"
      loop:
        - name: user1
          uid: 1011
        - name: user2
          uid: 1012
[root@main playkongzhi]# ansible servera -a 'id user1'
servera | CHANGED | rc=0 >>
uid=1011(user1) gid=1011(user1) groups=1011(user1)
[root@main playkongzhi]# ansible servera -a 'id user2'
servera | CHANGED | rc=0 >>
uid=1012(user2) gid=1012(user2) groups=1012(user2)

二.条件判断（when）

1.作用

（1）条件判断用于此任务的结果依赖变量、fact或者是上一个任务的结果，用条件判断就可以决定如何去执行对应的任务。在节点上建立了限制，捕获那些命令的输出，结果不同，执行的任务要求不同。

（2）可以判断某服务的配置文件是否发生变动时考虑是否重启。

（3）可以根据cpu状况来定制合适的调优策略

2.when语句的比较运算符

（1）!=/==用于比较两个对象是否不等/相等，可用于字符串、数字类型

示例


[root@main playkongzhi]# cat bijiao.yaml 
---
- hosts: servera
  tasks:
    - name: com them
      debug:
        msg: '等于'
      when: name == owner
  vars:
    name: sulibao
    owner: sulibao
ok: [servera] => {
    "msg": "等于"
}

（2）>/<，>=/<=用于比较两个对象的大小

示例


[root@main playkongzhi]# cat bijiao.yaml 
---
- hosts: servera
  tasks:
    - name: com them
      debug:
        msg: 'hello'
      when: name >= owner
  vars:
    name: sul
    owner: li
    
ok: [servera] => {
    "msg": "hello"
}

3.when语句的逻辑运算符

（1）and，逻辑与，两个对象同真为真


[root@main playkongzhi]# cat when.yaml 
---
- hosts: servera
  tasks:
    - name: dis info
      debug:
        msg: "yes"
      when: 1 > 0 and 1 < 9
      
ok: [servera] => {
    "msg": "yes"
}

（2）or，逻辑或，两个对象见真为真


[root@main playkongzhi]# cat when.yaml 
---
- hosts: servera
  tasks:
    - name: dis info
      debug:
        msg: "yes"
      when: 1 > 0 or 1 < 9
ok: [servera] => {
    "msg": "yes"
}

（3）not，逻辑否，取反


[root@main playkongzhi]# cat when.yaml 
---
- hosts: servera
  tasks:
    - name: dis info
      debug:
        msg: "yes"
      when: not 1 > 0 and 1 < 9
skipping: [servera]

（4）()，作为一个更大的表达式包含一组表达式


[root@main playkongzhi]# cat when.yaml 
---
- hosts: servera
  tasks:
    - name: dis info
      debug:
        msg: "yes"
      when: (not 1 > 0 and 1 < 9) or 5 < 6
      
ok: [servera] => {
    "msg": "yes"
}

4.when语句的exists判断

（1）判断目录是否存在


[root@main playkongzhi]# cat test.yaml 
---
- hosts: servera
  tasks:
    - debug:
        msg: "directory exist"
      when: path is exists
  vars:
    path: /root
    
ok: [servera] => {
    "msg": "directory exist"
}

（2）判断文件是否不存在，取反操作


[root@main playkongzhi]# cat test.yaml 
---
- hosts: servera
  tasks:
    - debug:
        msg: "file not exist"
      when: not path is exists
  vars:
    path: /root/ansible.bak
    
ok: [servera] => {
    "msg": "file not exist"
}

5.when语句对于变量的判断

（1）defined，变量已被定义


[root@main playkongzhi]# cat varswhen.yaml 
---
- hosts: servera
  tasks:
    - name: test vars
      debug:
        msg: "var defined"
      when: inventory_hostname is defined
ok: [servera] => {
    "msg": "var defined"
}

（2）变量未被定义


[root@main playkongzhi]# cat varswhen.yaml 
---
- hosts: servera
  tasks:
    - name: test vars
      debug:
        msg: "var undefined"
      when: a is undefined
ok: [servera] => {
    "msg": "var undefined"
}

（3）变量被定义为空


[root@main playkongzhi]# cat varswhen.yaml 
---
- hosts: servera
  vars:
    a:
  tasks:
    - name: test vars
      debug:
        msg: "var none"
      when: a is none
      
ok: [servera] => {
    "msg": "var none"
}

6.when语句对于结果的判断

（1）success/succeeded，failure/failed判断任务任性成功与否


[root@main playkongzhi]# cat result.yaml 
---
- hosts: servera
  tasks:
    - name: cd result
      shell: "cd /cevd"
      ignore_errors: true   #为了测试结果完整，忽略错误
      register: result
    - name: test result
      debug:
        msg: "no directory /cevd"
      when: not result is success
ok: [servera] => {
    "msg": "no directory /cevd"
}

（2）change/changed，skip/skipped判断任务执行状态


[root@main playkongzhi]# cat result.yaml 
---
- hosts: servera
  tasks:
    - name: cd result
      shell: "touch /a.txt"
      ignore_errors: true
      register: result
    - name: test result
      debug:
        msg: "touch success"
      when: result is changed
ok: [servera] => {
    "msg": "touch success"
}

三.整体条件判断block

1.作用

解决when语句多个判断需要书写多个when的情况，使用block将多个任务组合起来，对这个整体进行when条件判断，条件成立了才会去执行块中的所有任务。在playbook中可以给block定义name，也可以直接使用when，但不能直接对其使用loop循环。这里主要介绍block常规用法，rescue错误处理用法和always固定执行用法

2.block用法示例


[root@main playkongzhi]# cat block.yaml 
---
- hosts: servera
  tasks:
    - name: carry block
      block:
        - name: free 
          shell: "free -m"
        - name: echo 
          shell: "free -m > /a.txt"
      when: 1 < 2
[root@main playkongzhi]# ansible servera -a 'cat /a.txt'
servera | CHANGED | rc=0 >>
              total        used        free      shared  buff/cache   available
Mem:           5848         306        5348          11         193        5313
Swap:          2047           0        2047

3.block错误处理时用法演示

没有/my目录，shell模块执行错误，执行rescue部分

注意：block模块中只要有一个任务执行失败都会跳转执行rescue部分


[root@main playkongzhi]# cat rescue.yaml 
---
- hosts: servera
  tasks:
    - name: test rescue
      block:
        - shell: "ls /my"
      rescue:
        - debug: 
            msg: "no directory"
ok: [servera] => {
    "msg": "no directory"
}

4.block固定执行用法演示

不管bloack块执行成功还是失败，都执行alway部分


[root@main playkongzhi]# cat always.yaml 
---
- hosts: servera
  tasks:
    - name: test rescue
      block:
        - shell: "ls /my"
      rescue:
        - debug: 
            msg: "no directory"
      always:
        - debug:
            msg: "there always"
ok: [servera] => {
    "msg": "no directory"
}
ok: [servera] => {
    "msg": "there always"
}

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原文地址：https://blog.csdn.net/weixin_64334766/article/details/134032136