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<preface id="introduction">
  <title>Introduction</title>
  <para>
    Reconnoiter is a monitoring and trend analysis system designed to cope
    with large architectures (thousands of machines and hundreds of thousands
    of metrics).
  </para>
  <para>
    Heavy focus is placed on decoupling the various components of the system
    to allow for disjoint evolution of each component as issues arise or new
    requirements are identified.  Resource monitoring, metric aggregation,
    metric analysis and visualization are all cleanly separated.
  </para>
  <para>
    The monitor, <command>noitd</command>, is written in C and designed to 
    support highly concurrent and rapid checks with an expected capability 
    of monitoring 100,000 services per minute (6 million checks per hour.)  
    While it is hard to make writing checks "easy" in this high-performance
    environment, efforts have been made to ensure that custom check scripting
    does not require the expertise of writing highly-concurrent, event-driven
    C code.  Instead, glue is provided via scripting languages such as Lua
    that attempt to handle aspects of this high-concurrency environment
    transparently.  As with any high-performance system, you can easily
    introduce non-performant code and jeopardize performance system-wide.
  </para>
  <para>
    The aggregator, <command>stratcond</command>, is also written in C and 
    responsible for the simple task of securely gathering data from all of the 
    distributed <command>noitd</command> instances and transforming them into 
    the data storage facility (currently PostgreSQL).
  </para>
  <para>
    The data storage facility (PostgreSQL) holds all information about
    individual checks, their statuses and the individual metrics associated
    with them.  Automatic processes are in place that summarize the
    numeric metrics into windowed averages for expedient graphing at
    a variety of time window resolutions (hour, day, month, year, etc.).
  </para>
  <para>
    The visualization interface (reconnoiter) draws from the data store
    to visualize collected metrics and assist with monitoring, trending and
    other visual analyses.  The visualization system is written in PHP.
  </para>
</preface>
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