The eG Installation Guide - eG Innovations

Introduction
specification and control, database storage, threshold computation, alarm correlation, and user
interactions.
1.1.2 Agents
The agents monitor the environment by running periodic tests. The outputs of the tests are called
measurements. A measurement determines the state of a network / system / application / service
element of the target environment. For example, a Process test reports the following measurements:
1. Number of processes of a specific type executing on a system.
2. The CPU utilization for these processes
3. The memory utilization for these processes
Agents use different approaches for testing the target environment. The tests can be executed from
locations external to the servers and network components that are responsible for the operation of the
IT infrastructure. Agents that make such tests are called external agents. These agents take an
external view of the IT infrastructure and indicate if the different services supported by the IT
infrastructure are functioning properly or not.
Often external agents alone may not be sufficient to completely gauge the health of an IT
infrastructure and to diagnose problems when they occur. For example, it may not be possible to
measure the CPU utilization levels of a web server from an external location. To accommodate such
situations, eG Enterprise uses internal agents. An internal agent runs on a server that supports the
IT infrastructure and monitors various aspects pertaining to the server (e.g., CPU, memory, and disk
utilization, the processes executing on it, and the applications).
For making measurements, eG agents support various mechanisms. The Simple Network Management
Protocol (SNMP) continues to be the standard for monitoring network elements (routers, load
balancers, WAP gateways, etc.). Besides monitoring network elements, eG agents also manage
systems and applications. SNMP is rarely supported at the application layer. Hence, for monitoring
applications, eG agents support various other mechanisms:
1. Emulated transactions: By emulating typical transactions from clients to different applications,
eG agents monitor various aspects of the server. For example, to measure the health of a web
server, eG Enterprise uses an HttpTest that emulates user accesses to the web server.
Depending on whether and when a response is received or not, as well as based on the status
code returned by the server in the Hyper Text Transport Protocol (HTTP) response returned by
the server, the eG agent assesses the availability of the web server and the response time for
the request.
2. SNMP data collection: To monitor the various network elements and any other application
components that support SNMP, eG agents support SNMP-based monitoring.
3. OS-specific instrumentation: Server operating systems already collect a host of statistics
regarding the health of the server and processes executing on it. For example, CPU, memory,
and disk space utilizations, network traffic statistics, process-related measures can all be
collected using operating system specific hooks. eG agents use these hooks to collect and
report a variety of statistics of interest.
4. Application specific adapters: For monitoring specific applications, an eG agent uses custom
adapters. One example of a custom adapter is the web adapter. The key motivation for the
web adapter technology is that even today log files produced by web servers continue to be
the predominant mode of monitoring web servers. Logging has several drawbacks. Since each
and every request received by the web server is recorded in the logs, each request produces a
disk access that can be an expensive operation. Moreover, large web sites that get millions of
hits a day can produce logs that are several terabytes in size. Processing these log files is
extremely expensive (in terms of CPU and memory overheads on the server). Consequently,
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