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Agent vs. agentless security: Learn the differences

Enterprises can either use an agent or agentless approach to monitor and secure their networks. Each approach has benefits and drawbacks.

Network monitoring and security revolve around two main approaches: agent-based and agentless. Both have advantages and disadvantages. It's important to understand the implications of each before deciding which option to deploy and where.

The basic difference between them is this:

  • Agent-based products rely on an application installed on the system that's being monitored.
  • Agentless software uses APIs -- primarily -- to communicate directly with monitored resources.

There is more to it than that, particularly when looking to monitor a legacy system versus a cloud platform. Let's dig a little deeper to understand how to effectively weigh agent vs. agentless security.

What is agent-based security?

Agent-based products use specialized software components installed on individual endpoints of a network that an organization wants to monitor and protect. The agent continuously monitors the endpoint, collecting security-related data, as well as patch and vulnerability status information, which is then sent automatically or on demand to a centralized management system. This approach provides real-time insights into the security of each endpoint. Because the agent is semi-autonomous, it can react immediately to enforce defined security policies and initiate actions such as system restarts and configuration changes.

Agent-based security advantages

Agent-based products offer a straightforward and well-understood way to monitor and control endpoints. They are popular for the following reasons:

  • Real-time support. Because the agent is located directly on the device, it can provide customized in-depth scanning and monitoring in real time. It can also react immediately to device-specific security events or problems, even operating as a firewall to manage network connections based on filtering rules.
  • Responsive. It can send telemetry to a central security platform, apply patches and configuration changes, and perform power management tasks to save power and improve security.
  • Decentralization. Agents decentralize the security model. Because they operate independently of any central management server, they are more resilient to network issues. This makes them ideal for networks with limited bandwidth and devices within DMZs or with limited or no network connectivity. They can be installed on any compatible device and there is no need to integrate them with third-party services and APIs.
  • Not dependent on connectivity. Agents aren't dependent on network connectivity for security, making them suitable for remote locations or devices with limited bandwidth. They are also good for networks where users and devices are only intermittently connected.

Agent-based security disadvantages

The big downside of agent-based security is the complexity and work involved in installing and configuring agents across multiple devices. Even if the rollout can be automated, administrators still must monitor the deployment process because human error or missed devices can create unidentified gaps in security coverage.

Other challenges include the following:

  • Scalability limitations. The need to install an agent on each device or system means it doesn't scale well, particularly in large, complex and distributed environments that change quickly.
  • Potential vulnerabilities. Agents are privileged, networked processes but not immune to attack. CVEs have been reported for various security agents, and a compromised agent would be a serious security threat to the device and potentially the entire network. Updating every agent takes time, leaving open a window of opportunity for attackers to exploit a new vulnerability before agents are patched.
  • Working with disparate software and hardware. The need to monitor different device types running different OSes can reduce the choice of suitable products that can be deployed, particularly when an infrastructure includes IoT devices in addition to standard servers and PCs.
  • Labor-intensive. Switching between agent-based security products is labor-intensive. Existing agents need to be removed before the new ones can be installed, imposing a level of vendor lock-in.
  • Performance degradation. Agents can degrade the performance of devices with limited memory or CPU resources. This can be an issue depending on the number and complexity of the tasks an endpoint executes because it can lead to lower performance and even push cloud compute nodes into higher-priced deployment tiers.

What is agentless security?

Agentless security puts more emphasis on the overall security of the IT environment rather than individual endpoints. Security data needed to build an infrastructure inventory and monitor that inventory is gathered, collated and analyzed by a central control system using noninvasive methods such as APIs and log inspection. This removes the need to install software agents on every endpoint across a network or distributed environment. This also means that everything from serverless services and VMs to PaaS and SaaS can be monitored, and even devices where it's not possible to install a software agent. Cloud providers' APIs can also be tapped to collect additional data about workloads and device health.

Agentless security advantages

Another advantage of agentless security is it can immediately begin reporting on and managing any device found on the network. Agent-based systems can only monitor machines that have an agent actively running. This reduces the deployment of agentless security to a fraction of the time needed for an on-device agent rollout. At the same time, agentless security delivers greater initial coverage and visibility across the entire infrastructure.

The following are among other benefits:

  • Scalability. Because there is no need to install an agent on each new device, agentless security scales easily, automatically discovering new resources as they're created.
  • Reduced maintenance. There is no need to update agents when a vendor implements new features, making it virtually maintenance-free. In addition, there isn't any code installed that could potentially introduce vulnerabilities into the device and thus the network.
  • Resource efficiency. Agentless security is lightweight and less resource-hungry than installed agents. Rollout and ongoing running costs are lower. Because the central service collects data via APIs, the performance impact on device workloads is minimal. This can be crucial for IoT devices with limited onboard resources.
  • Flexibility. Switching security providers and even using multiple services simultaneously is easier because agentless security is nonintrusive and there is unlikely to be any conflict between services.

Agentless security disadvantages

Despite solving many of the problems associated with agents, consider the following drawbacks of agentless:

  • Fragility in safeguarding processes. Agentless security depends on network connectivity and uses secure tunnels to connect to endpoints located on the outer edges of the network. This adds fragility to safeguarding processes. The risk of downtime can cause compliance and security issues, so even though agentless security isn't as resource-intensive as agent-based security, it requires a strong infrastructure and dedicated hardware to ensure system reliability.
  • No true real-time monitoring or active runtime protection. Security data cannot be collected at the same level of detail, and APIs and log files can only provide snapshots of a device's status and health. As a result, true real-time monitoring and active runtime protection aren't possible.
  • Automation challenges. Managing security policies and settings on individual endpoints can be harder to automate as there is no direct access to them.
  • Compatibility. Like agent-based security, compatibility issues can occur, particularly in hybrid environments with both cloud and on-premises resources.

Agent vs. agentless: Which is better?

Having measured agent-based and agentless security, it's clear that either is viable depending on the specific use case or environment. It's important, therefore, to consider the benefits and limitations of both approaches against the organization's particular requirements and priorities.

While agent-based security offers more comprehensive and real-time protection and doesn't rely on network connectivity, its heavy resource consumption can rule it out as an option for certain devices. Agent-based security is also more labor-intensive because each device needs to be onboarded, configured and maintained. Agentless security, on the other hand, involves only a one-time setup on the central control server. This makes it more flexible and scalable for networks hosting disparate devices, saving time and effort.

The type of security approach your organization takes depends on its security and compliance requirements, as well as network environment. Agent-based systems are a prudent choice for mission-critical, on-premises systems where security and reliability are paramount. Agent-based security prevents gaps that might occur due to connectivity issues even as it performs any necessary actions if the device becomes disconnected from the main network. In contrast, an agentless system would be a better and simpler choice for complex, large-scale, solely cloud-based environments where resources are constantly spinning up and down, or where a large number of devices are not easily accessible, such as in industrial control systems.

In reality, a combination of agent and agentless security will deliver the most comprehensive security. But this is an option for only those companies with the biggest security budgets.

Michael Cobb, CISSP-ISSAP, is a renowned security author with more than 20 years of experience in the IT industry.

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