Ansible Playbooks Phần 3: Conditionals, Loops và Tags

Phần 3 tập trung vào control flow với Conditionals, Loops và Tags để tạo playbooks linh hoạt và mạnh mẽ.

Phần 3: Conditionals, Loops và Tags:

Conditionals (when) cho control flow
Loops: simple, dictionaries, nested
Loop với conditionals và register
Tags cho selective execution
Blocks và error handling (block/rescue/always)
Ví dụ multi-tier deployment

Conditionals (Điều kiện)

Chạy task chỉ khi điều kiện thỏa mãn sử dụng when.

Basic conditionals

tasks:
  - name: Install Apache on Debian/Ubuntu
    apt:
      name: apache2
      state: present
    when: ansible_os_family == "Debian"

  - name: Install Apache on RedHat/CentOS
    yum:
      name: httpd
      state: present
    when: ansible_os_family == "RedHat"

  - name: Start service only on production
    service:
      name: nginx
      state: started
    when: env == "production"

Multiple conditions với and

tasks:
  - name: Install package on Ubuntu 20.04
    apt:
      name: nginx
      state: present
    when:
      - ansible_distribution == "Ubuntu"
      - ansible_distribution_version == "20.04"

  # Hoặc viết trên một dòng
  - name: Same as above
    apt:
      name: nginx
      state: present
    when: ansible_distribution == "Ubuntu" and ansible_distribution_version == "20.04"

Multiple conditions với or

tasks:
  - name: Install on Debian or Ubuntu
    apt:
      name: nginx
      state: present
    when: ansible_distribution == "Debian" or ansible_distribution == "Ubuntu"

  # Hoặc dùng list
  - name: Install on Debian family
    apt:
      name: nginx
      state: present
    when: ansible_distribution in ["Debian", "Ubuntu"]

Conditions với registered variables

tasks:
  - name: Check if nginx is installed
    command: which nginx
    register: nginx_check
    ignore_errors: yes

  - name: Install nginx if not present
    apt:
      name: nginx
      state: present
    when: nginx_check.rc != 0

  - name: Check disk usage
    shell: df -h / | awk 'NR==2 {print $5}' | sed 's/%//'
    register: disk_usage

  - name: Warning if disk > 80%
    debug:
      msg: "WARNING: Disk usage is {{ disk_usage.stdout }}%"
    when: disk_usage.stdout|int > 80

Conditions với facts

tasks:
  - name: Install specific version on old Ubuntu
    apt:
      name: nginx=1.18.0-0ubuntu1
      state: present
    when:
      - ansible_distribution == "Ubuntu"
      - ansible_distribution_major_version|int < 22

  - name: Set timezone on physical machines
    timezone:
      name: Asia/Ho_Chi_Minh
    when: ansible_virtualization_role != "guest"

Conditions với file checks

tasks:
  - name: Check if config exists
    stat:
      path: /etc/nginx/nginx.conf
    register: config_file

  - name: Backup config if exists
    copy:
      src: /etc/nginx/nginx.conf
      dest: /etc/nginx/nginx.conf.backup
      remote_src: yes
    when: config_file.stat.exists

  - name: Create config if not exists
    copy:
      src: templates/nginx.conf
      dest: /etc/nginx/nginx.conf
    when: not config_file.stat.exists

Conditions với boolean

vars:
  install_monitoring: true
  enable_ssl: false

tasks:
  - name: Install monitoring agent
    apt:
      name: node-exporter
      state: present
    when: install_monitoring

  - name: Configure SSL
    template:
      src: ssl.conf.j2
      dest: /etc/nginx/ssl.conf
    when: enable_ssl | bool

Loops

Lặp qua danh sách items để thực thi task nhiều lần.

Simple loop

- name: Install multiple packages
  apt:
    name: "{{ item }}"
    state: present
  loop:
    - nginx
    - git
    - vim
    - htop
    - curl

Loop với dictionaries

- name: Create multiple users
  user:
    name: "{{ item.name }}"
    state: present
    groups: "{{ item.groups }}"
    shell: "{{ item.shell }}"
  loop:
    - { name: 'john', groups: 'developers', shell: '/bin/bash' }
    - { name: 'jane', groups: 'admins', shell: '/bin/bash' }
    - { name: 'bob', groups: 'developers', shell: '/bin/zsh' }

- name: Create directories with permissions
  file:
    path: "{{ item.path }}"
    state: directory
    owner: "{{ item.owner }}"
    mode: "{{ item.mode }}"
  loop:
    - { path: '/opt/app', owner: 'appuser', mode: '0755' }
    - { path: '/var/log/app', owner: 'appuser', mode: '0755' }
    - { path: '/etc/app', owner: 'root', mode: '0644' }

Loop với variables

vars:
  packages:
    - nginx
    - postgresql
    - redis
  
  users:
    - alice
    - bob
    - charlie

tasks:
  - name: Install packages
    apt:
      name: "{{ item }}"
      state: present
    loop: "{{ packages }}"

  - name: Create users
    user:
      name: "{{ item }}"
      state: present
    loop: "{{ users }}"

Loop với conditionals

- name: Install packages only on Ubuntu
  apt:
    name: "{{ item }}"
    state: present
  loop:
    - nginx
    - apache2
    - mysql-server
  when: ansible_distribution == "Ubuntu"

- name: Create users only in production
  user:
    name: "{{ item }}"
    state: present
  loop:
    - produser1
    - produser2
  when: env == "production"

Loop với register

- name: Check multiple services
  systemd:
    name: "{{ item }}"
  register: service_status
  loop:
    - nginx
    - mysql
    - redis

- name: Display service status
  debug:
    msg: "{{ item.item }} is {{ item.status.ActiveState }}"
  loop: "{{ service_status.results }}"

Nested loops

- name: Create files in multiple directories
  file:
    path: "{{ item.0 }}/{{ item.1 }}"
    state: touch
  loop: "{{ directories | product(files) | list }}"
  vars:
    directories:
      - /tmp/dir1
      - /tmp/dir2
    files:
      - file1.txt
      - file2.txt

Loop control

- name: Install packages with index
  apt:
    name: "{{ item }}"
    state: present
  loop:
    - nginx
    - git
    - vim
  loop_control:
    index_var: idx
    label: "Installing {{ item }}"

- name: Process with pause between iterations
  command: process_item.sh {{ item }}
  loop:
    - item1
    - item2
    - item3
  loop_control:
    pause: 5  # Pause 5 seconds between iterations

Loop until

- name: Wait for service to be ready
  uri:
    url: http://localhost:8080/health
    status_code: 200
  register: health_check
  until: health_check.status == 200
  retries: 10
  delay: 5  # Wait 5 seconds between retries

Tags

Tags giúp chạy selective tasks.

Basic tags

tasks:
  - name: Install nginx
    apt:
      name: nginx
      state: present
    tags:
      - install
      - nginx
      - packages

  - name: Configure nginx
    template:
      src: nginx.conf.j2
      dest: /etc/nginx/nginx.conf
    tags:
      - configure
      - nginx

  - name: Start nginx
    service:
      name: nginx
      state: started
    tags:
      - service
      - nginx

Running with tags

# Chỉ chạy tasks có tag 'install'
ansible-playbook site.yml --tags install

# Chỉ chạy tasks có tag 'nginx'
ansible-playbook site.yml --tags nginx

# Chạy nhiều tags
ansible-playbook site.yml --tags "install,configure"

# Skip tasks có tag 'service'
ansible-playbook site.yml --skip-tags service

# List available tags
ansible-playbook site.yml --list-tags

Special tags

tasks:
  - name: Always run this
    debug:
      msg: "This task always runs"
    tags: always

  - name: Never run this automatically
    debug:
      msg: "This only runs with --tags never"
    tags: never

  - name: Tagged task
    debug:
      msg: "Normal tagged task"
    tags: custom

# Task với tag 'always' sẽ chạy
ansible-playbook site.yml --tags install

# Skip task có tag 'always'
ansible-playbook site.yml --skip-tags always

# Chỉ chạy task có tag 'never'
ansible-playbook site.yml --tags never

Play-level tags

- name: Install packages
  hosts: web
  tags: install
  tasks:
    - name: Install nginx
      apt:
        name: nginx

    - name: Install git
      apt:
        name: git

- name: Configure services
  hosts: web
  tags: configure
  tasks:
    - name: Configure nginx
      template:
        src: nginx.conf.j2
        dest: /etc/nginx/nginx.conf

Block with tags

- name: Installation block
  block:
    - name: Update apt cache
      apt:
        update_cache: yes

    - name: Install packages
      apt:
        name: "{{ item }}"
        state: present
      loop:
        - nginx
        - git
  tags: install

- name: Configuration block
  block:
    - name: Copy configs
      template:
        src: "{{ item }}.j2"
        dest: "/etc/{{ item }}"
      loop:
        - nginx.conf
        - app.conf
  tags: configure

💡 Key Takeaways

Conditionals (when) control task execution dựa trên điều kiện
Loops iterate qua lists hoặc dictionaries
Tags cho phép chạy selective tasks
Blocks group tasks và provide error handling
Combine conditionals + loops + tags để tạo playbooks mạnh mẽ

🎯 Thực hành

Viết playbook với conditionals cho different OS families
Sử dụng loops để tạo multiple users và directories
Tag tasks theo categories (install, configure, deploy)
Implement error handling với block/rescue/always

Ansible Playbooks Phần 3: Conditionals, Loops và Tags

Conditionals (Điều kiện)

Basic conditionals

Multiple conditions với and

Multiple conditions với or

Conditions với registered variables

Conditions với facts

Conditions với file checks

Conditions với boolean

Loops

Simple loop

Loop với dictionaries

Loop với variables

Loop với conditionals

Loop với register

Nested loops

Loop control

Loop until

Tags

Basic tags

Running with tags

Special tags

Play-level tags

Block with tags

💡 Key Takeaways

🎯 Thực hành

Mục lục

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