Comprehensive comparison for DevOps technology in Software Development applications

---
# Ansible Playbook: Deploy Multi-Tier Web Application with Blue-Green Deployment
# This playbook demonstrates production-grade deployment of a web application
# with database migrations, health checks, and rollback capabilities

- name: Deploy Web Application with Blue-Green Strategy
  hosts: webservers
  become: yes
  vars:
    app_name: "customer-api"
    app_version: "{{ lookup('env', 'APP_VERSION') | default('1.0.0', true) }}"
    app_port_blue: 8080
    app_port_green: 8081
    deployment_color: "{{ lookup('env', 'DEPLOY_COLOR') | default('blue', true) }}"
    app_user: "appuser"
    app_base_dir: "/opt/{{ app_name }}"
    health_check_retries: 5
    health_check_delay: 10

  pre_tasks:
    - name: Validate deployment parameters
      assert:
        that:
          - app_version is defined
          - app_version is match('^[0-9]+\.[0-9]+\.[0-9]+$')
          - deployment_color in ['blue', 'green']
        fail_msg: "Invalid deployment parameters. Version must be semantic (x.y.z) and color must be blue or green"

    - name: Create application user
      user:
        name: "{{ app_user }}"
        system: yes
        shell: /bin/bash
        create_home: yes

  tasks:
    - name: Install required system packages
      apt:
        name:
          - python3-pip
          - nginx
          - postgresql-client
        state: present
        update_cache: yes
      when: ansible_os_family == "Debian"

    - name: Create application directory structure
      file:
        path: "{{ item }}"
        state: directory
        owner: "{{ app_user }}"
        group: "{{ app_user }}"
        mode: '0755'
      loop:
        - "{{ app_base_dir }}/{{ deployment_color }}"
        - "{{ app_base_dir }}/logs"
        - "{{ app_base_dir }}/config"

    - name: Copy application configuration
      template:
        src: "templates/app_config.yml.j2"
        dest: "{{ app_base_dir }}/config/config.yml"
        owner: "{{ app_user }}"
        group: "{{ app_user }}"
        mode: '0640'
      notify: restart application

    - name: Deploy application artifact
      copy:
        src: "artifacts/{{ app_name }}-{{ app_version }}.tar.gz"
        dest: "{{ app_base_dir }}/{{ deployment_color }}/"
        owner: "{{ app_user }}"
        group: "{{ app_user }}"
      register: artifact_deployed

    - name: Extract application files
      unarchive:
        src: "{{ app_base_dir }}/{{ deployment_color }}/{{ app_name }}-{{ app_version }}.tar.gz"
        dest: "{{ app_base_dir }}/{{ deployment_color }}/"
        remote_src: yes
        owner: "{{ app_user }}"
        group: "{{ app_user }}"
      when: artifact_deployed.changed

    - name: Install Python dependencies
      pip:
        requirements: "{{ app_base_dir }}/{{ deployment_color }}/requirements.txt"
        virtualenv: "{{ app_base_dir }}/{{ deployment_color }}/venv"
        virtualenv_command: python3 -m venv
      become_user: "{{ app_user }}"

    - name: Run database migrations
      command:
        cmd: "{{ app_base_dir }}/{{ deployment_color }}/venv/bin/python manage.py migrate --no-input"
        chdir: "{{ app_base_dir }}/{{ deployment_color }}"
      become_user: "{{ app_user }}"
      environment:
        DATABASE_URL: "{{ lookup('env', 'DATABASE_URL') }}"
      register: migration_result
      failed_when: migration_result.rc != 0
      changed_when: "'No migrations to apply' not in migration_result.stdout"

    - name: Create systemd service file
      template:
        src: "templates/app.service.j2"
        dest: "/etc/systemd/system/{{ app_name }}-{{ deployment_color }}.service"
        mode: '0644'
      notify: reload systemd

    - name: Start application service
      systemd:
        name: "{{ app_name }}-{{ deployment_color }}"
        state: started
        enabled: yes
        daemon_reload: yes

    - name: Wait for application to be ready
      uri:
        url: "http://localhost:{{ app_port_blue if deployment_color == 'blue' else app_port_green }}/health"
        status_code: 200
        timeout: 5
      register: health_check
      until: health_check.status == 200
      retries: "{{ health_check_retries }}"
      delay: "{{ health_check_delay }}"
      failed_when: health_check.status != 200

    - name: Update nginx configuration to point to new deployment
      template:
        src: "templates/nginx_site.conf.j2"
        dest: "/etc/nginx/sites-available/{{ app_name }}"
        mode: '0644'
      notify: reload nginx

    - name: Enable nginx site
      file:
        src: "/etc/nginx/sites-available/{{ app_name }}"
        dest: "/etc/nginx/sites-enabled/{{ app_name }}"
        state: link
      notify: reload nginx

    - name: Validate nginx configuration
      command: nginx -t
      register: nginx_test
      changed_when: false
      failed_when: nginx_test.rc != 0

  post_tasks:
    - name: Stop old deployment
      systemd:
        name: "{{ app_name }}-{{ 'green' if deployment_color == 'blue' else 'blue' }}"
        state: stopped
      ignore_errors: yes

    - name: Record deployment metadata
      copy:
        content: |
          version: {{ app_version }}
          deployed_at: {{ ansible_date_time.iso8601 }}
          deployed_by: {{ ansible_user_id }}
          color: {{ deployment_color }}
        dest: "{{ app_base_dir }}/{{ deployment_color }}/deployment.info"
        owner: "{{ app_user }}"
        group: "{{ app_user }}"

  handlers:
    - name: reload systemd
      systemd:
        daemon_reload: yes

    - name: restart application
      systemd:
        name: "{{ app_name }}-{{ deployment_color }}"
        state: restarted

    - name: reload nginx
      systemd:
        name: nginx
        state: reloaded