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ansible / Deploying Applications
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Deploying Applications

Deploying an application involves multiple steps: pulling code, installing dependencies, configuring services, and restarting. Ansible playbooks can automate the entire deployment process.

Example: Deploy a Python Web App (Flask)

Assume we have a Flask app in a Git repository. The playbook below deploys it to a server.
---
- name: Deploy Flask application
  hosts: webservers
  become: yes
  vars:
    app_user: flaskapp
    app_dir: /opt/flaskapp

  tasks:
    - name: Ensure system packages are installed
      apt:
        name:
          - python3-pip
          - python3-venv
          - git
        state: present
        update_cache: yes

    - name: Create application user
      user:
        name: "{{ app_user }}"
        system: yes
        state: present

    - name: Clone repository
      git:
        repo: https://github.com/example/flaskapp.git
        dest: "{{ app_dir }}"
        version: main
        force: yes
      notify: restart app

    - name: Create virtual environment
      command: python3 -m venv venv
      args:
        chdir: "{{ app_dir }}"
      become_user: "{{ app_user }}"

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

    - name: Copy systemd service file
      template:
        src: flaskapp.service.j2
        dest: /etc/systemd/system/flaskapp.service
      notify: restart app

    - name: Start and enable service
      service:
        name: flaskapp
        state: started
        enabled: yes

  handlers:
    - name: restart app
      systemd:
        name: flaskapp
        state: restarted
        daemon_reload: yes

Using a Deployment Role

For production, consider creating a role. It makes the deployment reusable across projects. The role could have variables for repo URL, branch, and service name.

Blue‑Green Deployment (Simple Approach)

You can use Ansible to switch symlinks or update load balancer configurations. For example, clone the new version to a separate directory, test it, then switch the symlink:
- name: Deploy new version to staging directory
  git:
    repo: "{{ repo_url }}"
    dest: "{{ app_dir }}_{{ timestamp }}"
    version: "{{ version }}"

- name: Run smoke tests (custom module or script)
  command: "{{ app_dir }}_{{ timestamp }}/test.sh"

- name: Switch symlink
  file:
    src: "{{ app_dir }}_{{ timestamp }}"
    dest: "{{ app_dir }}"
    state: link
  notify: restart app

Rollbacks

Keep previous releases. To roll back, simply point the symlink to the previous directory and restart.


Two Minute Drill
  • Automate code checkout with git module.
  • Use pip module with virtual environments for Python apps.
  • Deploy as a systemd service using templates.
  • Implement blue‑green by switching symlinks for zero‑downtime.

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