【自动化运维神器Ansible】template流程控制：for循环与if条件判断详解

目录

1 流程控制概述

1.1 什么是流程控制

1.2 流程控制的类型

1.3 流程控制的重要性

2 条件判断（if/elif/else）

2.1 基本语法

2.2 简单条件判断

2.3 比较运算符

2.4 逻辑运算符

2.5 实际应用案例：根据操作系统类型配置Nginx

3 循环（for循环）

3.1 基本语法

3.2 遍历列表

3.3 遍历字典

3.4 循环控制变量

3.5 实际应用案例：配置多个Nginx虚拟主机

3.6 带条件的循环

3.7 循环中的else语句

4 嵌套循环与复杂场景

4.1 嵌套循环

4.2 循环中的特殊语法

4.3 实际应用案例：配置多个负载均衡后端服务器

5 宏（Macro）的高级应用

5.1 宏的定义与调用

5.2 带默认参数的宏

5.3 实际应用案例：使用宏简化虚拟主机配置

6 总结

在Ansible模板管理中，我们经常需要根据不同条件生成不同的配置内容，或者对列表、字典等复杂数据结构进行迭代处理。Jinja2模板引擎提供了强大的流程控制功能，包括for循环和if条件判断，使得模板能够根据实际情况动态生成配置内容。

{% if condition %}<!-- 条件为真时执行的代码 -->
{% elif another_condition %}<!-- 另一个条件为真时执行的代码 -->
{% else %}<!-- 所有条件都为假时执行的代码 -->
{% endif %}

{% if debug %}debug = true
{% else %}debug = false
{% endif %}

{% if value > 10 %}<!-- value大于10 -->
{% endif %}{% if version == "1.0" %}<!-- version等于"1.0" -->
{% endif %}{% if name in ["nginx", "apache", "httpd"] %}<!-- name在列表中 -->
{% endif %}

{% if condition1 and condition2 %}<!-- condition1和condition2都为真 -->
{% endif %}{% if condition1 or condition2 %}<!-- condition1或condition2至少一个为真 -->
{% endif %}{% if not condition %}<!-- condition为假 -->
{% endif %}

---
- hosts: webserversvars:nginx_config:user: "{{ ansible_user | default('nginx') }}"worker_processes: "{{ ansible_processor_vcpus }}"keepalive_timeout: 65tasks:- name: Configure nginxtemplate:src: nginx.conf.j2dest: /etc/nginx/nginx.conf

• 模板文件nginx.conf.j2：

user {{ nginx_config.user }};
worker_processes {{ nginx_config.worker_processes }};{% if ansible_distribution == "CentOS" %}error_log /var/log/nginx/error.log warn;pid /var/run/nginx.pid;
{% elif ansible_distribution == "Ubuntu" %}error_log /var/log/nginx/error.log;pid /run/nginx.pid;
{% endif %}events {worker_connections 1024;multi_accept on;
}http {include /etc/nginx/mime.types;default_type application/octet-stream;sendfile on;tcp_nopush on;tcp_nodelay on;keepalive_timeout {{ nginx_config.keepalive_timeout }};types_hash_max_size 2048;{% if ansible_distribution_major_version == "7" %}# CentOS 7 specific configurationssl_protocols TLSv1 TLSv1.1 TLSv1.2;{% elif ansible_distribution_major_version == "8" %}# CentOS 8 specific configurationssl_protocols TLSv1.2 TLSv1.3;{% endif %}# ... 其他配置
}

{% for item in sequence %}<!-- 对序列中的每个item执行的代码 -->
{% endfor %}

{% for server in servers %}server {{ server }};
{% endfor %}

{% for key, value in config.items() %}{{ key }} = {{ value }}
{% endfor %}

• Jinja2提供了多个循环控制变量：

---
- hosts: webserversvars:virtual_hosts:- name: "example.com"root: "/var/www/example.com"server_name: "example.com www.example.com"index: "index.html index.htm"- name: "test.com"root: "/var/www/test.com"server_name: "test.com www.test.com"index: "index.html"tasks:- name: Configure virtual hoststemplate:src: virtual_hosts.conf.j2dest: /etc/nginx/conf.d/virtual_hosts.conf

• 模板文件virtual_hosts.conf.j2：

{% for host in virtual_hosts %}
server {listen 80;server_name {{ host.server_name }};root {{ host.root }};index {{ host.index }};location / {try_files $uri $uri/ =404;}{% if host.name == "example.com" %}location /status {stub_status on;access_log off;allow 127.0.0.1;deny all;}{% endif %}
}
{% endfor %}

{% for host in virtual_hosts if host.enabled %}
server {# 配置内容
}
{% endfor %}

{% for item in items %}{{ item }}
{% else %}<!-- 如果items为空或未定义，则执行此代码 -->No items found
{% endfor %}

{% for category in categories %}[{{ category.name }}]{% for product in category.products %}{{ product.name }} = {{ product.price }}{% endfor %}
{% endfor %}

{% for user in users %}{{ user.name }}{% if not loop.last %},{% endif %}
{% endfor %}

---
- hosts: load_balancersvars:upstreams:- name: "app_servers"servers:- name: "app1"address: "192.168.10.10:8080"weight: 3- name: "app2"address: "192.168.10.11:8080"weight: 2- name: "app3"address: "192.168.10.12:8080"weight: 1- name: "api_servers"servers:- name: "api1"address: "192.168.2.10:8080"weight: 1tasks:- name: Configure upstreamstemplate:src: upstreams.conf.j2dest: /etc/nginx/conf.d/upstreams.conf

• 模板文件upstreams.conf.j2：

{% for upstream in upstreams %}
upstream {{ upstream.name }} {{% for server in upstream.servers %}server {{ server.address }} weight={{ server.weight }}{% if not loop.last %};{% endif %}{% endfor %}
}
{% endfor %}server {listen 80;server_name example.com;location / {proxy_pass http://app_servers;}location /api {proxy_pass http://api_servers;}
}

{% macro server_block(name, port) %}
server {listen {{ port }};server_name {{ name }};# ... 其他配置
}
{% endmacro %}{% for server in servers %}{{ server_block(server.name, server.port) }}
{% endfor %}

{% macro server_block(name, port=80, root="/var/www") %}
server {listen {{ port }};server_name {{ name }};root {{ root }};# ... 其他配置
}
{% endmacro %}

{% macro virtual_host(name, root, server_names, port=80) %}
server {listen {{ port }};server_name {{ server_names }};root {{ root }};index index.html index.htm;location / {try_files $uri $uri/ =404;}location /status {stub_status on;access_log off;allow 127.0.0.1;deny all;}
}
{% endmacro %}{{ virtual_host(name="example.com",root="/var/www/example.com",server_names="example.com www.example.com",port=80
) }}{{ virtual_host(name="test.com",root="/var/www/test.com",server_names="test.com www.test.com",port=80
) }}