[fusion-trac] #137: Support multiple hosts for tile maps

[Fusion]

#137: Support multiple hosts for tile maps
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   Reporter:  jbirch       |       Owner:  madair
       Type:  enhancement  |      Status:  new   
   Priority:  P2           |   Milestone:  2.0   
  Component:  Widgets      |     Version:  SVN   
   Severity:  Major        |    Keywords:        
External_id:               |       State:  New   
    Browser:  All          |          Os:  All   
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 One of the limiting factors of perceived performance for tiled maps is
 that (by RFC) the number of active HTTP 1.1 connections to a server should
 be limited to 2.  This providers a very small pipeline for service
 multiple images, javascript files, and other supporting resources.
 !OpenLayers works around this by allowing you to specify multiple hosts to
 retrieve tiles from as a comma-separated list, and accesses them in a
 round-robin fashion.  This could either be used to make requests to
 several load-balanced tile servers, or a single server with multiple DNS
 host entries pointing to it.

 To my understanding, Fusion currently requires that the user specify a
 single !MapGuide !MapAgent or !MapServer CGI in its config file, and then
 uses that for all requests of that type.

 I am not sure what the implications of this would be (does !OpenLayers
 also round-robin non-image requests?) but I believe that an ideal system
 would use a single host from the list per-client for all non-map requests
 so that you don't run into session problems, but would use a list of hosts
 for tiled map requests.

 One way of supporting this would be to leave the WebTierURL specification
 in the config.json file alone (and use this for non-mapimage requests),
 and add an extension to the Map element to specify which hosts to retrieve
 maps from.  Again, I'm not sure of how this would work with
 Fusion/OpenLayers internals, but it seems like the least invasive
 approach, and would also lend itself well to defining external sources for
 non-!MapGuide/!MapServer map types.

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Ticket URL: <http://trac.osgeo.org/fusion/ticket/137>
Fusion <http://trac.osgeo.org/fusion>
Fusion is a web-mapping application development framework for MapServer and MapGuide OS.