Agent or agentless monitoring? It's your choice

* The pros and cons of agent and agentless system mgmt. monitoring

An interesting trend is happening in system management: the coming together of agent and agentless monitoring. In the past, these two approaches were typically an either or kind of choice where customers had to choose philosophically through their product choices (typically an all or nothing choice), or physically - using agent-based monitoring on their more critical servers and agentless monitoring on servers that weren't as business sensitive. Interestingly, some management vendors are responding by giving customers a choice of both approaches.

Agent-based monitoring and management have been the bread and butter of management for many years. Its management functionality justified the time and effort it took to deploy and maintain the agent infrastructure. Then a few years ago, ITers started complaining about the extra work that is required to use agents, including the need to deploy multiple agents to one device because different management tools each have their own agent.

Some management vendors started offering agentless monitoring solutions as an alternative to their agent technologies, with some manufacturers offering only agentless technologies. Some of these offerings, although called agentless, actually used native agents of devices for monitoring or gathering management data. Other products gathered information through standards such as WMI (Windows Management Instrumentation, Microsoft's implementation of Common Information Model), which obviated the need for agents.

Several management vendors have told EMA that their customers were asking for a quick discovery method that could first tell them what was out there. Once they had that information, the customers could decide where to deploy agents. In response, several system management vendors added IP-based discovery to their repertoire in order to find the devices that are on the network. So now customers have a choice - using agentless or agent-based, or both.

An example of this trend is BMC's Performance Manager, which now includes both agentless and agent-based technologies, giving customers a choice. And there are examples of this trend in other management products, such as Mercury Interactive's SiteScope, which offers agentless monitoring capabilities.

Agentless typically provides lightweight monitoring, with limited depth of data gathering or monitoring capabilities. In addition, without code or management intelligence installed on the system, the opportunities for management are little to none. The advantage is the ease of deployment - there is no need to deploy the agents - as well as the ease of maintenance. Despite its limitations, if the agentless monitoring provides all that you need for a specific device, then it is probably the right choice for you.

The agent-based approach requires deployment and maintenance of the agents on the managed systems. Some agent approaches use remote management, so an agent is not necessary on every managed device, which reduces the number of agents that need to be managed. On the other hand, the agent-based approaches can gather more management data and more depth of information because of the agent instrumentation that is sitting on the system.

In addition, the agent-based approaches can deliver management capabilities through the interaction of the agents and the management servers. In short, the agent-based products offer more robust management (including monitoring) capabilities than the agentless varieties. As a side note, agent-based technologies can be more expensive than agentless - although I'm sure that there are exceptions to this.

If you're already using agent-based approaches and are not satisfied with the time that it takes to manage the agent infrastructure, or your company will not tolerate the installation of additional code on systems, you may want to take a look at some of the agentless technologies that are available to see if they may be a fit for you.

It's not an all or nothing choice - you can use agentless for systems that don't need robust management, while using agent-based products for the systems where robust management does matter. There may or may not be a cost differential for mixing the approaches on your systems, as compared to an all-agent deployment. As the management vendors are starting to give you a choice - exercise that choice where it makes most sense.

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