ELM Agents - Real-time, Poll-based, and Agentless Monitoring

ELM provides great flexibility and scalability for collecting data and monitoring systems. This can be accomplished with different types of agents. However, there are certain limitations in the monitoring capabilities of agents you should be aware of when planning your initial deployment or extending your existing license. In addition to monitoring capabilities, there are other performance factors to consider when either a service agent or virtual agent could be utilized to perform the same monitoring function.

Service Agent

A Service Agent is an executable (TNTAgent.exe) with companion files. The TNTAgent.exe process is installed as the TNT Agent service on the monitored computer. It communicates with an ELM Server via TCP sockets and all communications are encrypted and authenticated. Service Agents can be installed on Windows 2000, Windows XP, Windows Vista, Windows Server 2003, and Windows Server 2008 computers. All Monitor Items assigned to a Service Agent are executed within the TNTAgent.exe process. Only Service Agents can monitor systems in real-time.

Pros

• Distributes some of the CPU cycles required to monitor the computer to the computer being monitored. The amount of CPU used by a Service Agent depends on the configured monitor items and their scheduled intervals, and the amount of data to be collected.
• Provides system-level caching. If the ELM Server or network between the ELM Server and Agent computer is unavailable, the Agent process will cache data to the Agent's local disk drive, then transmit the data when connectivity is restored.
• Provides user defined parameters for setting minimum and maximum cache size and file location.
• Provides single TCP socket port connectivity to the ELM Server, which is necessary if a firewall separates the ELM Server and Agent computer.
• Less network bandwidth is required for communication between the ELM Server and the Service agent on the monitored computer.
• ELM Server service account must have administrative privileges for only one task (Agent Monitor auto-restart).

Cons

• Adds overhead to the monitored system.
• Service Agents must be updated when upgrading ELM.

Virtual Agents

A Virtual Agent provides remote monitoring. No software is installed on the monitored system. Virtual Agents can be used to monitor Windows systems and as well as network devices. All Monitor Items assigned to a Virtual Agent are executed within the ELM Server process running on the ELM Server computer. Many of them use RPC Win32 API calls and therefore require RPC and NetBIOS connectivity between the ELM Server and the Agent for Windows systems.

Pros

• Uses less processor CPU on the monitored computer.
• No software is installed on the monitored computer.
• Use to monitor IP-based network devices

Cons

• Higher network overhead due to authentication, encryption, and other RPC functions.
• RPC and NetBIOS dependency make them firewall unfriendly
• Because Virtual Agents must run at scheduled intervals, Virtual Agents cannot be monitored in real-time.
• ELM Server service account requires administrative rights on all monitored computers.