Notes from 2020-02-27 Lunch n Learn

ansible-preso.md

Ansible and you

Configuration management

Definition: the systems engineering practice of handling changes systematically so that a system maintains its integrity over time.

In software, this generally means ensuring the consistency of the environment in which our applications run:

• the operating system
• versions of interpreters, libraries, packages, and other services on which our stuff depends
• configuration settings and other variables that influence the behavior of our stuff and all the rest

The goal is to define the state a server should be in precisely, and put the server into that state in a deterministic way

• Historically, by hand (ideally with careful documentation)
• Ad-hoc scripting
• Infrastructure as code

I should note here that Ansible can also be used for deployment, orchestration, and provisioning , but was developed first and foremost as a CM tool, which is how we're using it at BenchPrep, and what I'll be covering here.

Ansible features

• Ansible is an open-source CM tool, comparable to Chef, Puppet, or Salt
• Sponsored by RedHat
• It uses SSH to connect to servers and run tasks
• No agent to install on the target machines, and no designated server
• Push-based
• Tasks are idempotent
• The DSL is declarative, not procedural
• Easy to learn (familiar tasks, human-readable config format)

Installation

brew update; brew install ansible

Fancy installation for Pythonistas:

Don't: sudo pip install ansible

pip install --user pipx
pipx install ansible

Ansible concepts

• Inventory
• Modules
• Tasks
• Playbooks
• Roles

Inventory

• List of hosts to manage, in a text file.
• By IP address or DNS names
• Create groups with .ini-style square-bracket names example
• Ansible will look for hosts file in $PWD and /etc/ansible/
• Can also pass inventory specifically with -i argument
• -i allows for dynamic inventory: you can pass a script that outputs a list of hosts

Modules

• A unit of code for Ansible to execute
• Designed for some particular use: adding users, copying files, running system commands, etc
• Can be written in any language
  • Idempotent
  • Conforming to Ansible module API
    • JSON inputs for state config
    • JSON output reporting status
• There are lots already available

Tasks

• The execution of a module, with args and variables set
• Loops over inventory, or a specific host, group, or pattern
• Can be executed ad hoc with ansible at the command line
• Or combined into Playbooks, which execute a series of tasks sequentially

Playbooks

• The configuration language of Ansible
• Describe a set of tasks to execute sequentially
• Written in YAML
• Tasks are grouped into "plays"
• Handlers allow tasks to be run on notification of other tasks
• Playbooks can import or include other playbooks
• Variables
  • defined at different levels
  • used as config values
  • inserted into templates

[Demo - install postgres on local vagrant box]

Roles

• Package management for configuration
• Break up config into repeatable chunks
• Encapsulate and organize tasks
• DRYs out vars, templates, etc
• Directory structure convention
• Roles can be called from playbooks
• Shared via Ansible Galaxy

Ansible + Terraform

over to Josh