???note “The Pipeline So Far” - Lecture 12: We used Terraform to provision raw, blank hardware on FABRIC. - Lecture 14 (Next): We want to use Docker Swarm to deploy containers. - The Missing Link: The raw FABRIC nodes don’t have Docker installed. We need a way to configure them automatically to satisfy our course project requirements [1].
???note “Theory: Idempotency” - Writing a Bash script to install Docker is imperative and fragile. If you run mkdir twice, it crashes. - Ansible is based on the mathematical concept of Idempotency ($f(f(x)) = f(x)$). - An operation is idempotent if applying it multiple times has the same effect as applying it once. - Ansible modules check the current state first; if the software is already installed, it does nothing.
???note “Theory: Finite State Automata” - Ansible treats your infrastructure as a state machine. - $S_0$: The blank FABRIC node. - $Transition$: The Ansible Playbook (declarative code). - $S_{final}$: The node configured exactly as desired (Docker installed, security policies set).
???note “Agentless Design” - Unlike older tools (Chef/Puppet), Ansible is Agentless. It does not require a daemon running on the target machines. - It uses standard SSH, pushing Python modules to the targets, executing them, and tearing them down. - Inventory: A file mapping IP addresses to logical groups (e.g., [managers], [workers]). - Playbook: A YAML file describing the desired state.
???note “Creating the Playbook” - We will write a site.yml to install Docker on the nodes Terraform just built. ~~~yaml - hosts: all become: yes tasks: - name: Ensure Docker is installed apt: name: docker.io state: present - name: Ensure Docker service is running service: name: docker state: started ~~~ ???note “Executing the Playbook” ~~~bash ansible-playbook -i inventory.ini site.yml ~~~