Agent vs Agentless Orchestration Tools

Imagine you manage 500 network devices and you want to automate their configuration.
Before you pick a tool, one question matters:

Do you need to install software on every device, or not?

Agent-based tools require software on each device. Agentless tools do not.
The blueprint compares four tools on this axis: Chef, Puppet, Ansible, and SaltStack.

Agentless Architecture

An agentless tool manages devices without installing any dedicated software on them.
The control node connects to each device using a standard protocol like SSH and pushes commands directly.

Figure 1 – Agentless architecture

This approach has three clear benefits:

• Nothing to install, so deployment is fast

• Works with devices that cannot run third-party software, which covers most network equipment

• Lower resource footprint on the managed device

Agentless is the natural choice for network automation.
A router or switch rarely accepts custom software installed by a third party, but almost every network device supports SSH.

Agent-Based Architecture

An agent-based tool requires a small software component, called the agent, installed on every managed device.
The agent runs in the background and communicates with a central server, usually called the master.

Figure 2 – Agent-based architecture

Because the agent is always there, it can enforce the desired state continuously.
If someone makes a manual change on the device, the agent notices the difference and reverts it back to the expected configuration.

But the agent comes with a cost.
You must install and maintain it on every device, which is rarely practical on network equipment.
This is why agent-based tools are most common on servers and virtual machines, not on routers and switches.

When a change must be applied, who picks up the phone first: the controller or the device?
This is a different question from agent vs agentless, but the two axes usually come as a pair.

Agentless tools use push, and agent-based tools use pull.

Push Model

In a push model, the control node initiates the connection and sends the configuration to the device.
The device waits and only acts when a change arrives from the controller.