Ansible – Basics

AGENDA ✔

🐱‍💻 Learn about Inventory File and inter-connectivity setup between resources

🐱‍💻 Configure inventory file

🐱‍💻 Execute and Debug inventory file.

🐱‍💻 Learn Blocks of inventory file.

🐱‍💻 Learn best practice and produce final file.

Pre-Requisite

🐱‍💻 One machine with ansible, python Installed. (Control machine)

🐱‍💻 Two machines with python installed (nodes)

🐱‍💻 Interconnectivity via ssh (This is a task to solve!)

WHAT IS INVENTORY FILE IN ANSIBLE.

An inventory file in ansible is list of managed hosts declared under a host group using either hostnames or IP addresses in a plain text file upon which commands, modules, and tasks in a playbook operate.
-The file can be in one of many formats depending on your Ansible environment and plugins

• Default location : /etc/ansible/hosts and Alternate locations are allowed.
• There are TWO TYPES of inventories.
• STATIC : User defined and has fixed/Static values
• DYNAMIC : Takes input from certain script to populate it’s contents.
• Ansible usually connects to it’s hosts defined in the inventory via SSH (Unix based systems) and WinRM (windows systems).

Configure inventory file.

• Added the inventory file.
• added node1 ansible_host=private_ip ansible_user=devops ansible_ssh_password = devops
• Similarly added details of node2
• 👆🏼 produced errors with

  ansible -i inventory-one -m ping node1

due to ssh_host_key_check, since instances are not authenticated with each other with ssh keys before this.

• Fixed Error
  modified /etc/ansible/ansible.cfg.
  – uncommented Host_key_checking = False
• -m ping node1 works now. {ping : pong}

the warning in the pink text can easily be fixed by updating python to python3. But current goal was to check connectivity between the Control and node.
(or follow this document.)

Ansible Groups

• The ansible Groups are variables that contain the information about the hosts
• Groups in a inventory file are convenient way to apply configuration to multiple hosts at once.
• Refer this document for configuration.

Push SSH_KEY into the new server for connectivity and authentication support

• login as devops user in control machine and cd /home/devops/.ssh/

  [devops@ansible-engine .ssh]$ sudo ssh-copy-id devops@172.31.35.246   #private_ip_dbserver
  Are you sure you want to continue connecting (yes/no)? yes
  devops@172.31.35.246's password: devops
  Number of key(s) added: 1

  Now try logging into the machine, with:   "ssh 'devops@172.31.35.246'"
  and check to make sure that only the key(s) you wanted were added.

• This should add public key (content of id_rsa.pub) to authorized keys of dbserver.
• test group works.

    ansible -i inverntory-one -m ping dbserver

• If you get SUCCESS! {Ping:Pong} then it worked, test for webserver group as well

Group and Children

• As groups are convenient to apply config to multiple but selective hosts, there is a mechanism called Children groups which are basically Group of Groups in an inventory file
  these children can be defined with [name_of_choice:children] followed by name of groups as we defined hosts.

  [myapp:children]
  webservers
  dbserver

• This can help apply same config to group of groups, as in maybe in a situation you need your certain app installed on only application servers and web-servers but do not want it on adatabse servers. So you simply define Children accordingly.
• Variables can be applied to such children via [children_name:vars]
• There are certain rules to be followed to avoid headache!
• Any host that is member of a child group is automatically a member of the parent group.
• A child group’s variables will have higher precedence (override) a parent group’s variables.
• Groups can have multiple parents and children, but not circular relationships.
• Hosts can also be in multiple groups, but there will only be one instance of a host, merging the data from the multiple groups

-The variables can be given at Host level or Group level

• the best practice is to give same parameters to group-hosts so that group level variables may be assigned to all relevant hosts at once.
• E.g Same User, Same Password, Same Interpreter..
• [all:vars] list/block defines variable that are common across infrastructure available.
• [group_name:vars] block can be defined to hold variables for specific group.
• The clean, good-practice followed file inventory-ok is now added for comparison.
• It’s evidently more readable and better visible than it’s predecessor.
• Refer this documentation for more insight.
• Here is the test

Here, I wrap this exercise about ANSIBLE INVENTORY and little bit of connectivity.
See you in next blog!