Infrastructure as Code
Describe your infrastructure in textual format and configure them using that description
Never perform system and software configurations manually
Use templates / scripts describing how to install / configure systems /devices /software / users
Configuration Management Systems make this possible
Convergence
Rather than describing the steps needed to make a change, the language describes the final state in which one wants to end up
The agent then ensures that the necessary steps are taken to end up in this "policy compliant state"
Thus, configuration can be run again and again, whatever the initial state of a system, and it will end up with a predictable result
Agent vs Agent-less
Advantages of Agent based
Rich client can do more and run on a schedule
Low volume of network traffic
Advantages of Agent-less based
Small memory footprint and support of rare systems
No need to run an agent all the time on each server
Ansible
Ansible Design Principles
Have a dead simple setup process and a minimal learning curve
Manage machines very quickly and in parallel
Avoid custom-agents and additional open ports, be agentless by leveraging the existing SSH daemon
Describe infrastructure in a language that is both machine and human friendly
Focus on security and easy auditability/review/rewriting of content
Manage new remote machines instantly, without bootstrapping any software
Allow module development in any dynamic language, not just Python
Be usable as non-root
Be the easiest IT automation system to use, ever
Ansible Terminology
The following list contains a quick overview of the most relevant terms used by Ansible:
Control Node: the machine where Ansible is installed, responsible for running the provisioning on the servers you are managing.
Inventory: an INI file that contains information about the servers you are managing.
Playbook: a YAML file containing a series of procedures that should be automated.
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.
Role: a set of related playbooks, templates and other files, organized in a pre-defined way to facilitate reuse and share.
Play: a provisioning executed from start to finish is called a play.
Facts: global variables containing information about the system, like network interfaces or operating system.
Handlers: used to trigger service status changes, like restarting or reloading a service.
Ansible Components
Inventory: The list of servers and optionally variables to operate on
Playbook: The collection of "plays" in YAML format to operate on the servers
Plays: A list of tasks and handlers to execute on each targeted server
Tasks: Instructions to cary out the configuration
Inventory File
The inventory files tells Ansible what servers to act on
Ansible allow you to place servers into groups (e.g., webservers, dbservers) and then make changes on entire groups of servers at the same time instead of changing them one-by-one
Groups allow you to specify servers of the same type
Hierarchy of Groups
Playbooks
Ansible stores itβs instructions in files called "Playbooks"
Expressed in YAML language
Composed of one or more "plays" in a list
Allows for multi-machine deployment orchestration
Playbook β Tasks
Are executed in the order they are specified against all machines that match the host pattern
May be included from other files
If a task fails, the remaining playbook are not executed for that host
Each task executes a module with specific options
Modules are idempotent in order to bring the system to a desired state
Playbook β Handlers
Notifications may be triggered at the end of each block of tasks that modify the remote system
Handlers are referred to by name and can perform operations like restarting services that have had their configuration changed
Example Playbook
python.yaml
:
Roles
Based on a know file structure
webservers.yaml
:
Vagrant Integration
Ansible is supported by Vagrant so that you can use the same Ansible Playbooks to configure your local VM and remote servers
Example 1: LAMP STACK
This will install Apache, MySQL, & PHP on Linux (LAMP)
Example 2: Same LAMP STACK but better
A better way would be to use the iteration of with_items
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