collection 4 - An efficient graphing front-end for collectd
=============================================================
<http://octo.it/c4/>

About
-----

  collection 4 (c4) is a web-based front-end to the RRD files updated by
  collectd. It is designed to be highly efficient and handle large
  installations - with 50,000 and more RRD files - well.


Concepts
--------

  Graphs
  ------
  c4 lets you configure "graphs" in its config file. Each graph has a selector
  which determines which files will be used to draw the graph. The selector
  uses the host/plugin[-instance]/type[-instance] layout known from collectd.
  Each field of the selector may be one of two wildcard expressions:

    * "/any/"
      The field may be any value. The files will be grouped by the values of
      all "/any/" fields. Think of the "GROUP BY" SQL expression. Each grouping
      is called an "instance" which can be identified by the graph selector and
      the value of the "/any/" fields.

    * "/all/"
      As with the any-selector, the field may be any value. However, all files
      that only differ in the "/all/" field(s) will be printed in the same
      graph.

  Upon startup, c4 will read the configuration and scan the directory
  containing the RRD files. Each file is added to all matching graphs, either
  by adding it to the appropriate instance or by creating a new instance. I.e.
  each file may be used in multiple graphs.

  If a file does not match any graph, a "dynamic graph" matching only that file
  will be created. This allows the front-end to display all files even when
  there is no explicit graph definition for them.

  Data providers
  --------------
  The idea is to encapsulate all the functions specific to one write plugin of
  collectd using an interface for querying data. This allows to program the
  rest of the front-end in a way that doesn't rely on one specific storage
  back-end.

  Currently, the only data provider scans a directory for RRD files and uses
  the librrd to fetch data. The whole concept is still a bit of a work in
  progress and currently the code-base is still cluttered with "*_get_rrdargs"
  functions. The RRDtool generated graphs will likely be replaced by a graphing
  solution integrated in the C code (creating rendered graphics) and / or a
  JavaScript-based solution which renders graphs in the browser.

  In the future it shall be possible to use multiple data providers in
  parallel. The vision is to have multiple servers running RRDCacheD. Data is
  distributed to those servers using the "Hashed" match of collectd and then a
  unified interface is provided via c4.


Dependencies
------------

  c4 currently requires the following libraries:

  * libfcgi
    <http://www.fastcgi.com/>

  * librrd_th (thread-safe version of librrd)
    <http://oss.oetiker.ch/rrdtool/>

  * libyajl
    <http://lloyd.github.com/yajl/>

  The "configure" script is currently kept minimal. It may therefore be
  necessary to set the CPP- and LD-flags manually. In case of libyajl, which is
  not built with libtool, you may need to set the rpath, too.

  When building from the Git repository, you'll need to have flex and bison (or
  possibly lex and yacc) installed. These two programs are used to generate the
  code for parsing the config file. If you are building from a tarball, the
  generated .c and .h files are included and you don't need to have these
  programs installed.


Bugs
----

  * Sending a FLUSH command to the collectd process is not yet possible.
  * "*_get_rrdargs" functions and other RRDtool specific cruft is still all
    over the code-base.
  * The JSON-based interface is unstable.
  * Currently it's not possible to display more than one graph at a time.
    (With a very limited and undocumented exception.)
  * Speaking of which: There is no documentation.
  * ... (to be added)


License
-------

  collection 4 is licensed under the GNU Lesser General Public License (LGPL),
  version 2.1. The exact license terms are available in the file "COPYING" in
  the top source directory.

  c4 includes the JavaScript library "jQuery" which is dual-licensed under the
  MIT license and the GPL. The file "share/jquery-1.4.4.min.js" includes a
  license header which points you to more detailed information.

  c4 includes the JavaScript library "Highcharts" which is licensed under the
  Creative Commons Attribution-NonCommercial 3.0 License (CC-by-nc 3.0). This
  means that the library is free of charge for non-commercial use. The file
  "share/highcharts.js" includes a license header which points you to more
  detailed information. More information on Highcharts and licensing options is
  available from <http://www.highcharts.com/>.


Author
------

  Florian "octo" Forster <ff at octo.it>