Skip to content

Ansible intro

Ansible is an open-source automation tool for configuration management, application deployment, and orchestration. It uses YAML playbooks to describe the desired state of systems and communicates over SSH. It is agentless, which means there is no need to install anything on the target machines.

Why Ansible?

  • Agentless: No need to install extra software on managed machines;
  • Idempotent: Tasks can be run repeatedly without unwanted side effects;
  • Human-readable: Playbooks use YAML, easy to write and review;
  • Scalable: Manage a handful of servers or thousands with the same commands.

Some things we have inside a Dockerfile for instance are specific for docker. However, if you put the instructions in an ansible playbook, those can be executed outside docker, making this solution more reusable by different environments. If you are working with docker you could have also a playbook to have instructions that are targetted to the host and to the docker container.

Alternatives

If Ansible is not available, one could use:

  • Shell scripts with ssh and scp for manual automation;
  • Configuration management tools like Puppet or Chef (these often require agents on target mmachines);
  • Cloud-native tools such as AWS CloudFormation, Terraform, or Azure Resource Manager (for infrastructure provisioning).

Major components

  • Inventory: A list of machines (hosts) Ansible manages.
  • Modules: Small, reusable programs that perform one action (install a package, copy a file, manage a service, etc.).
  • Tasks: Single steps executed on target hosts; each task calls a module with parameters.
  • Plays: A mapping that says “run these tasks on these hosts”.
  • Playbooks: YAML files containing one or more plays. They describe how and which order, at what time and where, and what modules should be executed. It orchestrates the modules' execution.
  • Handlers: Special tasks executed only when notified by other tasks (useful for actions like restarting a service after config change).
  • Roles: Redistributable units of organization that allow users to share automation code easier.
  • Variables: Key–value pairs to parametrize playbooks, templates, and roles.

Simple test VM

Simple example, for instance, once you provision a cloud VM (e.g. almalinux vm).

sudo dnf -y install epel-release
sudo dnf -y install ansible
ansible --version

Create inventory file (inventory):

[local]
localhost ansible_connection=local

Create playbook file (simple.yml). This is a playbook with a single play and three tasks.

Simple
- name: Simple Ansible test on AlmaLinux
  hosts: local
  connection: local
  tasks:
    - name: Gather system facts
      setup:
    - name: Create a test file
      copy:
        dest: /tmp/ansible_hello.txt
        content: "Hello from Ansible at {{ ansible_date_time.iso8601 }}\n"
    - name: Show hostname
      debug:
        msg: "This VM's hostname is {{ ansible_hostname }}"

Run the line below and the file in /tmp/ should be created.

ansible-playbook -i inventory simple.yml

If one wants to use multiple machines, replace 'hosts: local' with 'hosts: all' in the simple.yml and update the inventory with the list of ip addresses. Also remove connection: local.

Further notes

List available modules:

ansible-doc -l

More details on a particular module (e.g. copy):

ansible-doc copy

Can also find modules docs online at: WEBSITE

Test connections:

ansible all -m ping -i inventory

Show inventory:

ansible-inventory --list -y -i inventory

Append extra verbose mode using -vvv:

ansible-playbook -i inventory simple.yml -vvv