Create Key-Pair

1. Generate SSH key pair:

   ssh-keygen -t ed25519 -C "ansible"

   • Enter path: /home/${USER}/.ssh/ansible
   • You'll see ansible (Private Key) and ansible.pub (Public Key)

Goal: Create 3 Servers and Configure with Ansible

Strategy to Create 3 Servers:

1) Download Docker Image

redhat/ubi9    latest    a169546264dd    12 days ago    210MB

• This is the free version of RHEL which doesn't require authentication to download

2) Create Custom Image with SSH Public Certificate

1. Go to project directory
2. Build the image:

   docker build -t rhel-server:v1.0 .

3. Run 3 containers mapping port 22 to different host ports:

   docker run -d -p 2222:22 --name rhel-server-1 rhel-server:v1.0
   docker run -d -p 2223:22 --name rhel-server-2 rhel-server:v1.0
   docker run -d -p 2224:22 --name rhel-server-3 rhel-server:v1.0

4. Check running containers:

   docker ps

3) SSH into the Machines

• Use your private key to connect to each server:

  ssh -i ~/.ssh/ansible root@172.17.0.1 -p 2222
  ssh -i ~/.ssh/ansible root@172.17.0.1 -p 2223
  ssh -i ~/.ssh/ansible root@172.17.0.1 -p 2224

Install Ansible

If Ansible is not installed, install it with:

sudo apt install ansible  # For Ubuntu

Configure Ansible

Inventory File

The inventory file contains server_name, IP address, and port.

Run this command to ping the servers:

ansible all -i inventory -m ping -u root --private-key ~/.ssh/ansible

• -m = module (the ping module is run)
• You'll receive a pong from the Python interpreter, meaning that it works

Set up Config File

Set up the config file ansible.cfg, then just run:

ansible all -m ping

Additional Commands

ansible all --list-hosts
ansible all -m gather_facts # This gives us information about the hosts which we can use to write scripts like ansible_distribution
ansible all -m gather_facts --limit hostname  # This is for checking values and cross-verifying with playbook to debug issues 

Package Management

ansible all -m dnf -a "update_cache=true"
ansible all -m dnf -a "update_cache=true" --become --ask-become-pass 

# Install Package
ansible all -m dnf -a "name=docker"
ansible all -m shell -a "dnf search podman"

Log Files

In the server you can go to this path:

/var/log/

dnf.log contains history of commands run. You can tail it and see the log entries.

Ansible Playbooks

Run Playbook

ansible-playbook install_apache.yml
ansible-playbook book.yml --become --ask-become-pass

Playbook Structure

In the playbook you write scripts in YAML format:

- hosts: all
  become: true
  tasks:
  
  - name: Update Repository Index
    dnf:
      update_cache: yes

  - name: Install Package
    dnf:
      name: httpd
      state: present
      
  - name: Check Installation
    shell: command_here
    register: result
    
  - name: Display Result
    debug:
      msg: "{{ result.stdout }}"

Package States

Use different state values:

• present - Install package (default behavior)
• absent - Remove package
• latest - Install/update to latest version

Cross-Platform Considerations

Running Across Different Distributions

Playbooks may fail for Ubuntu as they're written for dnf and Ubuntu needs apt.

Use conditional statements based on distribution:

- name: Install Apache on RedHat
  dnf:
    name: httpd
    state: present
  when: ansible_distribution == "RedHat"

- name: Install Apache on Ubuntu
  apt:
    name: apache2
    state: present
  when: ansible_distribution == "Ubuntu"

Universal Package Module

Use the package module for cross-platform package management:

# Works on both RedHat and Ubuntu automatically
- name: Install Git (universal)
  package:
    name: git
    state: present

- name: Install Python (universal)
  package:
    name: python3
    state: present

# For packages with different names per distro
- name: Install Apache (universal)
  package:
    name: "{{ 'httpd' if ansible_distribution == 'RedHat' else 'apache2' }}"
    state: present

# Multiple distributions with same package manager
- name: Install Nginx on RHEL-based systems
  dnf:
    name: nginx
    state: present
  when: ansible_distribution in ["RedHat", "CentOS", "Rocky", "AlmaLinux"]

Get Distribution Information

ansible all -m gather_facts --limit rhel1 | grep distribution

This command gets the specific distribution from the host.