Comprehensive comparison for DevOps technology in Software Development applications

---
# Ansible Playbook: Deploy Node.js Microservice with Zero Downtime
# This playbook demonstrates production-grade deployment of a microservice
# with health checks, rollback capability, and proper error handling

- name: Deploy Node.js API Microservice
  hosts: api_servers
  become: yes
  vars:
    app_name: "payment-api"
    app_user: "apiuser"
    app_directory: "/opt/{{ app_name }}"
    app_port: 3000
    health_check_endpoint: "http://localhost:{{ app_port }}/health"
    git_repo: "https://github.com/company/payment-api.git"
    git_version: "{{ version | default('main') }}"
    node_version: "18.x"
    max_health_check_retries: 30
    health_check_delay: 2

  pre_tasks:
    - name: Validate required variables
      assert:
        that:
          - app_name is defined
          - app_port is defined
          - git_repo is defined
        fail_msg: "Required variables are not defined"

  tasks:
    - name: Install Node.js repository
      shell: "curl -fsSL https://deb.nodesource.com/setup_{{ node_version }} | bash -"
      args:
        creates: /etc/apt/sources.list.d/nodesource.list
      when: ansible_os_family == "Debian"

    - name: Install required packages
      apt:
        name:
          - nodejs
          - git
          - build-essential
        state: present
        update_cache: yes
      when: ansible_os_family == "Debian"

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

    - name: Create application directory structure
      file:
        path: "{{ item }}"
        state: directory
        owner: "{{ app_user }}"
        group: "{{ app_user }}"
        mode: '0755'
      loop:
        - "{{ app_directory }}"
        - "{{ app_directory }}/releases"
        - "{{ app_directory }}/shared"
        - "{{ app_directory }}/shared/logs"

    - name: Generate release timestamp
      set_fact:
        release_timestamp: "{{ ansible_date_time.epoch }}"

    - name: Clone application code
      git:
        repo: "{{ git_repo }}"
        dest: "{{ app_directory }}/releases/{{ release_timestamp }}"
        version: "{{ git_version }}"
        force: yes
      become_user: "{{ app_user }}"
      register: git_clone

    - name: Install npm dependencies
      npm:
        path: "{{ app_directory }}/releases/{{ release_timestamp }}"
        production: yes
        state: present
      become_user: "{{ app_user }}"
      environment:
        NODE_ENV: production

    - name: Copy environment configuration
      template:
        src: templates/env.j2
        dest: "{{ app_directory }}/releases/{{ release_timestamp }}/.env"
        owner: "{{ app_user }}"
        group: "{{ app_user }}"
        mode: '0600'
      no_log: true

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

    - name: Flush handlers to reload systemd
      meta: flush_handlers

    - name: Stop existing service for deployment
      systemd:
        name: "{{ app_name }}"
        state: stopped
      ignore_errors: yes
      when: ansible_facts.services[app_name + '.service'] is defined

    - name: Update current release symlink
      file:
        src: "{{ app_directory }}/releases/{{ release_timestamp }}"
        dest: "{{ app_directory }}/current"
        state: link
        owner: "{{ app_user }}"
        group: "{{ app_user }}"

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

    - name: Wait for application to be healthy
      uri:
        url: "{{ health_check_endpoint }}"
        status_code: 200
        timeout: 5
      register: health_check
      until: health_check.status == 200
      retries: "{{ max_health_check_retries }}"
      delay: "{{ health_check_delay }}"
      failed_when: false

    - name: Rollback on health check failure
      block:
        - name: Stop failed deployment
          systemd:
            name: "{{ app_name }}"
            state: stopped

        - name: Find previous release
          find:
            paths: "{{ app_directory }}/releases"
            file_type: directory
            excludes: "{{ release_timestamp }}"
          register: previous_releases

        - name: Restore previous release
          file:
            src: "{{ (previous_releases.files | sort(attribute='mtime', reverse=true) | first).path }}"
            dest: "{{ app_directory }}/current"
            state: link
            force: yes
          when: previous_releases.files | length > 0

        - name: Start previous version
          systemd:
            name: "{{ app_name }}"
            state: started

        - name: Fail deployment
          fail:
            msg: "Deployment failed health check. Rolled back to previous version."
      when: health_check.status != 200

    - name: Clean up old releases
      shell: "ls -1dt {{ app_directory }}/releases/* | tail -n +6 | xargs rm -rf"
      args:
        warn: false
      when: health_check.status == 200

    - name: Log successful deployment
      lineinfile:
        path: "{{ app_directory }}/shared/logs/deployments.log"
        line: "{{ ansible_date_time.iso8601 }} - Successfully deployed {{ git_version }} ({{ release_timestamp }})"
        create: yes
        owner: "{{ app_user }}"
        group: "{{ app_user }}"
      when: health_check.status == 200

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