Ansible folder structure - vagrant

Question

I'm coming from a Puppet background using Vagrant and have some trouble making sense of Ansible and its differences.
My Puppet structure looked like this:
puppet
├── servers
│ └── Backend
│ └── Vagrantfile
└── src
├── manifests
│ └── nodes
│ └── development
│ └── backend.pp
└── modules
└── mysql
Setup was simple, cd to the Vagrantfile and fire up the VM with Vagrant.
Now this is my first draft of an Ansible folder structure:
ansible
├── servers
│ └── Backend
│ ├── Vagrantfile
│   └── ansible.cfg
└── sources
├── backend.yml
├── site.yml
├── inventories
│ └── development
│ ├── group_vars
│ │   ├── all
│ │ └── backend
│ └── hosts
├── playbooks
└── roles
└── mysql
Following questions now:
Is this best practise for Ansible or too close to Puppet?
Is it correct to treat backend.yml like a Puppet node manifest?
Where should I put site.yml and backend.yml? This example has them in the main directory while here it's in the 'plays' directory. What's the difference?
I think my group_vars in group_vars/backend aren't being used correctly, how do I access them?
Sources:
http://leucos.github.io/ansible-files-layout/
https://github.com/ansible/ansible-examples
https://github.com/enginyoyen/ansible-best-practises

Answer 1

In my case, I use following structures according environment complexity (check directory-layout) :
Simple environment
I use this structure when there is one environment or when I use playbooks in provision mode
ansible
├── inventory
│ ├── hosts
│ └── group_vars
│ └── my_group.yml
├── roles
│ └── mysql
├── ansible.cfg
├── README.md
├── playbook1.yml
└── playbook2.yml
In ansible.cfg, I use variable inventory = ./inventory in [default] in order to avoid setting inventory path with commands ansible-*.
Medium/Complex environment
I use this structure when there are more than one environment
ansible
├── inventories
│ ├── production
│ │ ├── hosts
│ │ └── group_vars
│ │ └── my_group.yml
│ └── development
│ ├── hosts
│ └── group_vars
│ └── my_group.yml
├── playbooks
│ ├── playbook1
│ │ ├── group_vars
│ │ │ └── my_group.yml
│ │ ├── roles
│ │ │ └── mysql
│ │ ├── README.md
│ │ └── site.yml
│ ...
├── README.md
└── ansible.cfg
In this case, there is a folder for each environments in ./inventories.
I prefer also to use a specific folder for each playbooks in order to be able to use easily a folder group_vars at playbook level as defined in variable precedence section. As environment become more complex, there are much more variables. A group_vars (and host_vars) in playbooks allows to defines common variables for all environment which makes there are less inventories variables.
Ultimate level environment
I already used Ansible to adresse systems with more than 5000 servers, here under some tips for adressing more complex environments :
Split inventory file
Use multiple files to define your inventory servers instead of a single hosts file. In this case hosts file contains only server's names, and other files contains groups with different perspectives :
└── production
├── hosts
├── middleware
└── trigram
middleware: Groups with mapping to used middlewares or other stuf. I use this file to map, for example, servers to tomcat, java, postgresql, etc. And I use it, for example, with playbooks that deploys monitoring agents : How to retrieve metrics, logs from tomcat, java, postgresql, etc.
trigram: On my project, I usually use codes with a fixed length (3 or 4) to identify my business components (ex. : 'STK' for stock management) then I create a group file to map a business component to my servers (which servers are used to deploy 'STK')
When you create a new playbook, choose your perspective to address different environments.
Caution : I think ansible load files with alphabetical name order, you can't define a group that refers a group not yet loaded.
Use folders for group_vars
In group_vars, instead of using files, you can use a folder with subfiles :
└── production
└── group_vars
└── my_group
├── vars1.yml
└── vars2.yml
This is usefull to split huge files or if you have tools that generate variables, in this case you have vars1.yml under git and vars2.yml is generated
Split git repo
When you are using ansible for huge system, there is a lot of commits and a question comes up often : How to split my huge git repo ?
I my case, I use one git repo for each folder in ./inventories with differents access rules. And a git repo for each folder in ./playbooks also with different access rules.

Answer 2

You found several examples of the recommended layout, but not the official one. That should hopefully answer many of your questions, but I'll try to address them here as well.
Is this best practise for Ansible or too close to Puppet?
It's definitely not the recommend layout for Ansible. In the best practices layout, there is no servers or sources - the things inside those all live at the top level (what does "servers" mean, anyways?).
Is it correct to treat backend.yml like a Puppet node manifest?
I'm not familiar with Puppet, and so can't answer this question.
Where should I put site.yml and backend.yml? This example has them in the main directory while here it's in the 'plays' directory. What's the difference?
The official recommendation has all playbooks splattered across the root directory. However, this gets a bit messy, so some people put them in a subdirectory (in your examples, plays). This works reasonably well, but you'll need to adjust the paths in your playbooks accordingly.
I think my group_vars in group_vars/backend aren't being used correctly, how do I access them?
You shouldn't put them in a subdirectory of the inventory folder, as they're not part of inventory. There are a number of places to define variables, and you should read the documentation to learn what they are and when you should use them, but group_vars should be at the root of the directory with everything else.