Introduction

Ansible is a modern automation tool that makes our lives easier by helping us manage our servers, deployments, and infrastructure. We declare what we want and let Ansible do the hard work. Some of the things that Ansible can do are as follows:

• Install and configure software
• Manage users and databases
• Deploy applications
• Remote execution
• Manage Infrastructure as Code

We will focus on the Infrastructure as Code part of Ansible for a significant part of this book.

Ansible has certain distinct advantages over other similar tools.

• Ansible is agentless. So we do not need to install any software on the servers that are to be managed. It does require Python runtime on the servers and a SSH server on remote hosts.
• Ansible supports both push and pull modes. So we can execute Ansible code from a central control machine to make changes on remote machines or the remote machines can pull configuration from a well defined source periodically.
• Code for Ansible is written in YAML (http://yaml.org/), which stands for YAML Ain't Markup Language. Ansible did not create and manage a language (or DSL) from scratch. YAML is easy to read, write, and understand. This makes up most of Ansible code's self documentation and reduces the learning curve of Ansible significantly.
• Ansible does not try to re-invent the wheel. Hence it uses SSH as a transport and YAML as a Domain Specific Language (DSL). In typical cases, there are two entities involved, a system (A) where the playbook execution is initiated, and another system (B), usually remote, which is configured using Ansible:

In a nutshell, Ansible helps to manage various components of servers, deployments and infrastructure in a repeatable manner. Its self-documenting nature helps with understanding and auditing true nature of infrastructure.

Infrastructure as Code

Traditionally, infrastructure has been managed manually. At best, there would be a user interface which could assist in creating and configuring compute instances. For most of the users who begin their journey with a cloud, a web-based dashboard is the first and most convenient way to interact. However, such a manual method is error prone. Some of the most commonly faced problems are:

• Requirement for more personnel to manage infrastructure round the clock
• Probability of errors and inconsistencies due to human involvement
• Lack of repeatability and auditability

Creating Infrastructure as Code addresses these concerns and helps in more than one way. A well maintained code base will allow us to refer to the infrastructure state, not only at the present but also at various points in the past.

Ansible helps us code various aspects of infrastructure including provisioning, configuring, and eventually, retiring. Ansible supports coding over 20 cloud providers and self-managed infrastructure setups. Due to its open nature, existing providers can be enhanced and customized and new providers can be added easily.

Once we start managing Infrastructure as Code, we open ourselves to the possibility of a lot of automation. While this book focuses on creating and managing the infrastructure, the possibilities are limitless. We can:

• Raise an alarm if a critical machine becomes unreachable.
• Personnel who do not have access to infrastructure can still help by coding the infrastructure. A code review exercise could help to enforce best practices.
• We can scale infrastructure dynamically based on our requirements.
• In case of a disaster, we can create replacements quickly.
• Passing knowledge of best practices within and outside the organization becomes easier.

Throughout this book, we will create our infrastructure from Ansible code and demonstrate its usability and repeatability.

Introduction of Ansible entities

Before we start diving into the Ansible world, we need to know some basics:

• Inventory: We need to have a list of hosts that we want to manage. Inventory is that list. In its simplest form, this can be a text file created manually which just lists the IP addresses of the servers. This is usually enough for small infrastructure or if the infrastructure is static in nature. It follows ini syntax and a typical inventory would look like this:

[webservers]
server1
[application]
server1
server2

If our infrastructure is dynamic, where we add and remove servers frequently, we can use dynamic inventory. This would allow us to generate the inventory in real time. Ansible provides dynamic inventory scripts for many cloud providers and allows us to create dynamic inventory scripts as per our need for non-standard setups. We will use dynamic inventory in this book since it is better suited to cloud based environments.

• Modules: Ansible modules are executable plugins that get the real job done. Ansible comes with thousands of modules which can do tasks from installing packages to creating a server. Most of the modules accept parameters based upon which they take suitable actions to move the server towards a desired state. While this book uses modules primarily in the YAML code, it is possible to use modules in command line as an argument to Ansible ad hoc command.
• Tasks: A task is a call to an Ansible module along with all the requirements like parameters, variables etc. For example, a task may call upon the template module to read a Jinja template and set of variables, and generate the desired state of a file for the remote server.
• Roles: Ansible roles describe the particular role that a server is going to play. It consists of YAML code which defines tasks. It also consists of the dependencies for the execution of tasks like required files, templates and variables.
• Playbooks: A playbook is a YAML file where we associate roles and hosts. It is possible to write the tasks in the playbook itself and not use roles but we would strongly discourage this practice. For the sake of readability and better code management, we suggest that playbooks should be kept small with just the name of the hosts or groups to target as defined in inventory and calls to the roles.
• Variables: Just like any other programming language, Ansible also has good old-fashioned variables. They hold values which can be used in tasks and templates to perform certain actions. Variables can be created before execution in a file or generated and modified during runtime. A very common use case is to invoke certain tasks if a variable holds a certain value or to store the output of a task in a variable and use it in one of the subsequent tasks.