有些时候，我们需要进行一些条件判断才决定是否执行某个操作，在playbook里面when语句帮我们解决了这个问题。
比如，如果节点的操作的系统为Debian那么就关机。
tasks: - name: "shut down Debian flavored systems" command: /sbin/shutdown -t now when: ansible_facts[‘os_family‘] == "Debian"
当然还可以进行更加复杂的操作,and和or的逻辑判断。
如果系统是centos6或者是Debian7，那么就关机。
tasks: - name: "shut down CentOS 6 and Debian 7 systems" command: /sbin/shutdown -t now when: (ansible_facts[‘distribution‘] == "CentOS" and ansible_facts[‘distribution_major_version‘] == "6") or (ansible_facts[‘distribution‘] == "Debian" and ansible_facts[‘distribution_major_version‘] == "7")
如果同时需要多个条件，那么可以这样：
tasks: - name: "shut down CentOS 6 systems" command: /sbin/shutdown -t now when: - ansible_facts[‘distribution‘] == "CentOS" - ansible_facts[‘distribution_major_version‘] == "6"
其实等价于下面：
tasks: - name: "shut down CentOS 6 and Debian 7 systems" command: /sbin/shutdown -t now when: (ansible_facts[‘distribution‘] == "CentOS" and ansible_facts[‘distribution_major_version‘] == "6")
有时候你会得到一个变量，它是一个字符串，你可以对其进行数学运算：
tasks: - shell: echo "only on Red Hat 6, derivatives, and later" when: ansible_facts[‘os_family‘] == "RedHat" and ansible_facts[‘lsb‘][‘major_release‘]|int >= 6
你还可以根据变量值，来判断：
变量值：
vars: epic: true
判断：
tasks: - shell: echo "This certainly is epic!" when: epic
还可以循环：
tasks: - command: echo {{ item }} loop: [ 0, 2, 4, 6, 8, 10 ] when: item > 5
配合变量寄存器：
- name: test play hosts: all tasks: - shell: cat /etc/motd register: motd_contents - shell: echo "motd contains the word hi" when: motd_contents.stdout.find(‘hi‘) != -1
ansible——playbook conditions条件判断
原文：https://www.cnblogs.com/yangmingxianshen/p/12657225.html