ansible——实施任务控制（循环loop、条件when）

一、编写循环任务

1. 简单循环

示例：不用循环时编写playbook

---

当使用循环变量item编写：

---
- name: test
  hosts: web
  tasks:
    - name: apache and vsftpd are running
      service:
        name: "{{ item }}"		
        state: started
      loop:
        - httpd
        - vsftpd
...

将变量放入列表：

2. 循环散列或字典列表

- name: User Test
  user:
    name: "{{ item.name }}"
    state: present
    groups: "{{ item.groups }}"
  loop:
    - name: westos
      groups: westos
    - name: redhat
      groups: root
##########早些版本的循环，使用with_#########
  vars:
    data:
      - user1
      - user2
      - user3
  tasks:
    - name: "with_items"
      debug:
        msg: "{{ item }}"
      with_items: "{{ data }}"

3. register和loop一起使用

---
- name: loop register test
  gather_facts: no	
  hosts: localhost
  tasks:
    - name: loop echo task
      shell: "echo This is my item: {{ item }}"
      loop:
        - one
        - two
      register: echo_results			#注册变量
    - name: Show echo results variable
      debug:
        var: echo_results			#显示变量结果
...

---

迭代上面 playbook 的结果(即使用上面 item 的结果)

二、条件任务语法

关键字：when
条件用于仅再符合特定条件时执行任务或 play

1.使用布尔值测试：

测试 my_service 变量是否有值，有值则安装：

---
- name: Boolean test
  hosts: all
  vars:
    my_service: my_service
  tasks:
    - name: "{{ my_service }} is installed"
      yum:
        name: "{{ my_service }}"
      when: my_service is defined
...

2.条件判断方式

等于（字符串） A == "B"
等于（数字） A == 100
小于 <
大于 >
小于等于 <=
大于等于 >=
不等于 !=
变量存在 xxx is defined
变量不存在 xxx is not defined
布尔值 true 1、true、yes
布尔值 false 0、false、no
第一个变量的值存在，且在第二个变量的列表中 A in B

（1）测试多个条件： or：两个条件一个为真即可；and：两个条件必须都为真
（2）when 支持使用列表描述条件：

when:
  - ansible_distribution_version == "8.0"
  - ansible_kernel == "4.18.0-80.1.2.el8_0.x86_64"
######再如：########
when:
  ( ansible_distribution == "RedHat" and ansible_distribution_major_version == "8" )
  or
  ( ansible_distribution == "CentOS" and ansible_distribution_major_version == "7" )

3 组合循环和有条件的任务

示例1：当循环变量挂载到根下并且大小不超过300M时，安装数据库。

---
- name: keyword
  hosts: all
  tasks:
    - name: install db if enough space
      yum:
        name: mariadb-server
        state: latest
      loop: "{{ ansible_mounts }}"    #此变量是事实，已知的
      when: item.mount == "/" and item.size_available > 300000000  #挂载到根下，大小不超过300M
...   

---

示例二：只有当vsftpd服务运行时，才能重启Apache

---
- name: Restart httpd if vsftpd is running
  hosts: all
  tasks:
    - name: Get vsftpd status
      command: /usr/bin/systemctl is-active vsftpd	#判断状态
      ignore_errors: yes	#如果vsftpd没运行或失败，则忽略,继续执行下面动作
      register: result		#定义变量保存结果
    - name: Restart httpd
      service:
        name: httpd
        state: restarted
      when: result.rc == 0  	#退出码为0，则重启httpd
...   

---

反向测试：当在受管主机中暂停vsftpd服务后，重新执行playbook

---

示例三：安装并启动数据库

编写playbook：

############基础写法################
- name: Mariadb is running
  hosts: web1
  vars:
    mariadb_pkgs:
      - mariadb-server
      - python3-PyMySQL
  tasks:
    - name: Mariadb is installed
      yum:
        name: "{{ item }}"
        state: present
      loop: "{{ mariadb_pkgs }}"
    - name: Start Mariadb
      service:
        name: mariadb
        state: started
        enabled: true
#修改 playbook，条件变为受管主机使用 rehdat 操作系统时才执行########
---
- name: Mariadb is running
  hosts: web1
  vars:
    mariadb_pkgs:
      - mariadb-server
      - python3-PyMySQL
  tasks:
    - name: Mariadb is installed
      yum:
        name: "{{ item }}"
        state: present
      loop: "{{ mariadb_pkgs }}"
      when: ansible_distribution == "RedHat"	#更改条件
...     

编辑完成后，先检测主机组系统：ansible web1 -m command -a ‘cat /etc/redhat-release’ -u student --become
检测完成后，再运行playbook