6 CD

Continuous Deployment

Table of Contents

1. Overview

   1.1. Ansible

2. Goal

3. Steps

   3.1. Prerequisites

   3.2. Create Ansible Roles

4. Best Practices

1. Overview

1.1. Ansible

• A playbook (written in YAML) defines one or more plays that will be executed on one or more remote machines (selected from inventory) through an SSH connection (no agent required).
• A play has a name (optional), vars (optional), target hosts (selected by patterns), a remote_user (e.g., root), one or more tasks to execute, and (optionally) one or more handlers to be notified to run when the play changes machine state.
• A task executes a [named] module (built-in or 3rd-party) against remote machines (default execution strategy is sequential).
• An inventory (YAML/INI file) contains [named groups of] IP addresses or hostnames of remote machines, it can also store variables.
• Ansible collects return codes from executed tasks, facts about remote machines and magic variables storing internal state.
• Role: the standard way to group related Ansible artifacts (vars, files, tasks, etc.) to share them so they can be loaded and reused.

2. Goal

• Getting familiar with Ansible by writing plays to automatically install docker and deploy one of the applications on the Vagrant VMs created during the previous phase.

3. Steps

3.1. Prerequisites

• Install Ansible CLI

• Apply terraform plan with vagrant provider from previous phase.

  cd terraform/vagrant
  terraform apply

• Forwarded SSH ports will be printed, note them down to use in Ansible config.

• Create inventory ansible/hosts.ini with configurations for connecting to VMs.

• Specify ansible_ssh_private_key_file=<key_file> in inventory.

  • Key files can be found in .vagrant directory which should be ignored from the VCS.

• Create project configuration ansible/ansible.cfg and override inventory file location to use the one just created.

  • You may also disable host_key_checking as it requires interactive input to add VMs to ~/.ssh/known_hosts.

• Test connection with ping module

  

• Install community.docker collection

  ansible-galaxy collection install community.docker

3.2. Create Ansible Roles

• Create 4 roles inside ansible/roles directory for:

  • Installing nginx on the loadbalancer VM with a given nginx.conf.
  • Installing docker on app VMs specified in hosts file.
  • Deploying application image with a given dockerhub_id and app_name
  • Wiping application from VMs.

• Write main.yml that executes such roles against the VMs.

• Test the roles: ansible-playbook main.yml

  

• Verify that docker is installed and application image is running

  

• Verify that app is running on http://localhost:8080

• You may also schedule Watchtower to automatically update app images from DockerHub.

4. Best Practices

• Documentation Reference

• A module should be responsible for one small simple task.

• Use the recommended directory structure for roles.

• Use ansible-playbook --check to check actions before taking them (not all modules support this).

  • Or try changes on staging environment first.

• Give tasks meaningful names, separate them with empty lines for readability, use comments for extra explanation.

• Use ansible-lint to lint playbooks.

• Use dynamic inventory when working with cloud hosts to avoid manual IP/hostname configurations.

• Use state to specify the desired module state so that modules won’t execute twice unless needed.