Ansible

Ansible is an open source IT Configuration Management, Deployment & Orchestration tool. It aims to provide large productivity gains to a wide variety of automation challenges. This tool is very simple to use yet powerful enough to automate complex multi-tier IT application environments.

Ansible Terms:

• Controller Machine: The machine where Ansible is installed, responsible for running the provisioning on the servers you are managing.
• Inventory: The “inventory” is a configuration file where you define the host information. In the above /etc/ansible/hosts example, we declared two servers under test-hosts.
• Playbook: In most cases – especially in enterprise environments – you should use Ansible playbooks. A playbook is where you define how to apply policies, declare configurations, orchestrate steps and launch tasks either synchronously or asynchronously on your servers. Each playbook is composed of one or more “plays”. Playbooks are normally maintained and managed in a version control system like Git. They are expressed in YAML (Yet Another Markup Language).
• Task: A block that defines a single procedure to be executed, e.g. Install a package.
• Module: A module typically abstracts a system task, like dealing with packages or creating and changing files. Ansible has a multitude of built-in modules, but you can also create custom ones.
• Role: A role is the Ansible way of bundling automation content and making it reusable. Roles are organizational components that can be assigned to a set of hosts to organize tasks. Therefore, instead of creating a monolithic playbook, we can create multiple roles, with each role assigned to complete a unit of work. For example: a webserver role can be defined to install Apache and Varnish on a specified group of servers.
• Play: A provisioning executed from start to finish is called a play. In simple words, execution of a playbook is called a play.
• Facts: Global variables containing information about the system, like network interfaces or operating system.
• Handlers: Handlers are similar to tasks except that a handler will be executed only when it is called by an event. For example, a handler that will start the httpd service after a task installed httpd. The handler is called by the [notify] directive. Important: the name of the notify directive and the handler must be the same.
• Templates: Templates files are based on Python’s Jinja2 template engine and have a .j2 extension. You can, if you need, place contents of your index.html file into a template file. But the real power of these files comes when you use variables. You can use Ansible’s [facts] and even call custom variables in these template files.
• Variables: As the name suggests, you can include custom-made variables in your playbooks. Variables can be defined in five different ways:

1. Variables defined in the play under vars_files attribute:
vars_files:
  - "/path/to/var/file"

2. Variables defined in <role>/vars/apache-install.yml

3. Variables passed through the command line:
ansible-playbook apache-install.yml -e "http-port=80"

4. Variables defined in the play under vars
vars: http_port: 80

5. Variables defined in group_vars/ directory

Ansible is a helpful tool that allows you to create groups of machines, describe how these machines should be configured or what actions should be taken on them. Ansible issues all commands from a central location to perform these tasks.

No other client software is installed on the node machines. It uses SSH to connect to the nodes. Ansible only needs to be installed on the control machine (the machine from which you will be running commands) which can even be your laptop. It is a simple solution to a complicated problem.

Advantages Of Using Ansible

Simple: Ansible uses a simple syntax written in YAML called playbooks. YAML is a human-readable data serialization language. It is extraordinarily simple. So, no special coding skills are required and even people in your IT organization, who do not know what is Ansible can likely read a playbook and understand what is happening. Ansible always executes tasks in order.

Agentless: Finally, Ansible is completely agentless. There are no agents/software or additional firewall ports that you need to install on the  client systems or hosts which you want to automate. You do not have to separately set up a management infrastructure which includes managing your entire systems, network and storage. Ansible further reduces the effort required for your team to start automating right away.

Powerful & Flexible: Ansible has powerful features that can enable you to model even the most complex IT workflows. In this aspect, Ansible’s batteries included approach (This philosophy means that something is self-sufficient, comes out-of-the-box ready to use, with everything that is needed) can manage the infrastructure, networks, operating systems and services that you are already using, as Ansible provides you with hundreds of modules to manage them. Together Ansible’s capabilities allow you to orchestrate the entire application environment regardless of where it is deployed.

Efficient: No extra software on your servers means more resources for your applications. Also, since Ansible modules work via JSON, Ansible is extensible with modules written in a programming language you already know. Ansible introduces modules as basic building blocks for your software. So, you can even customize it as per your needs. For e.g. If you have an existing message sending module which sends messages in plain-text, and you want to send images too, you can add image sending features on top of it.                                                                                                                                                    

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