Ansible

As a network engineer, you will frequently need to configure network devices using the CLI.
At first glance, this seems convenient: you log in to a device, type a few commands, and the configuration is done.

However, in real-world networks, typing commands manually in the CLI can quickly become time-consuming and prone to human errors.

Manual configuration at scale

Imagine you need to configure the same NTP server on multiple routers.
Instead of doing it once, you now need to:

• open your terminal software

• connect to each router using SSH

• manually type the same configuration commands

Figure 1 - Manual configuration of network devices

You must repeat this process for every network device that needs the configuration.
This approach is time-consuming and prone to human errors, especially as the number of devices increases.

Why automation becomes necessary

By using Ansible, you can apply configuration changes to multiple devices at the same time.

As shown below, the Ansible server connects to network devices using SSH and pushes the required configuration commands automatically.

Figure 2 – Centralized network device configuration using Ansible

Using Ansible is especially useful in medium to large networks, where it helps reduce deployment time and minimize human errors.

However, Ansible does not work by magic.
To use it effectively, you need to understand the key concepts behind how Ansible operates.

Ansible uses a push model to apply configuration changes.
This means that the Ansible server, also called the control node, pushes configuration changes directly to the destination devices.

These changes are defined in configuration files stored on the Ansible server and are applied by opening SSH connections to the network devices.

Figure 3 - Ansible agentless management using SSH from a central control node.

Push model and agentless architecture

This model is very convenient because network devices are agentless.
Agentless means that no additional software needs to be installed on the network devices for Ansible to work.

• The only requirement is that the devices are reachable using SSH.

Once SSH access is available, the Ansible server can connect to the devices and push configuration changes automatically.

Why this approach is useful

Using an agentless push model makes Ansible:

• easy to deploy

• compatible with many network devices

• well suited for network automation

This simplicity is one of the main reasons why Ansible is widely used for managing network device configurations.

Ansible works by using several key elements that work together to apply configuration changes to network devices.

Inventory – Where to apply changes

The inventory defines which devices Ansible will manage.