The dynamic map engine is a virtual map engine that provides load balancing and fail over support for other map engines.
When a dynamic map engine is configured, it is setup so that it points to one or more other map engines that all have the same configuration. Then anything that previously pointed to the original map engine is changed to point to the new map engine, or the old map engine is renamed and the dynamic map engine is given the id of the old map engine.
The dynamic map engine then provides fail over if one of the map engines fails or it will cycle between the map engines passing the incoming requests to each one it turn to provide load balancing.
The dynamic map engine is also useful for developers and administrators who need to test multiple map engines and don't want to have to change map engine id's in the client configuration. By referring to a dynamic map engine in the client map view configuration, the real map engine is specified in the dynamic map engine configuration and so can be changed without having to alter the client configuration.
<?xml version="1.0" encoding="UTF-8"?>
<config xmlns="urn:com.cohga.server.config#1.0"
xmlns:wms="urn:com.cohga.server.map.wms#1.0"
xmlns:dynamic="urn:com.cohga.server.map.dynamic#1.0">
<wms:mapengine id="wms1">
<url>http://server1.local/wms</url>
<!-- other WMS configuration items -->
</wms:mapengine>
<wms:mapengine id="wms2">
<url>http://server2.local/wms</url>
<!-- other WMS configuration items -->
</wms:mapengine>
<!-- will redirect all requests 'redirect' to 'wms1' -->
<dynamic:mapengine id="redirect">
<mapengine>wms1</mapengine>
</dynamic:mapengine>
<!-- will cycle requests for 'loadbalanced' between 'wms1' and 'wms2' -->
<!-- you can list as many map engines as you need but they must all be configured identically -->
<dynamic:mapengine id="loadbalanced">
<mapengine>wms1</mapengine>
<mapengine>wms2</mapengine>
</dynamic:mapengine>
<!-- will send requests for 'failover' to 'wms1' until that falls over, in which case it'll use 'wms2' -->
<!-- you can list as many map engines as you need but they must all be configured identically -->
<dynamic:mapengine id="failover">
<failover>true</failover>
<mapengine>wms1</mapengine>
<mapengine>wms2</mapengine>
</dynamic:mapengine>
<!-- will send requests for 'alternate' to 'wms1' unless the user turns on an aerial photo layer, in which case it will use 'wms2' -->
<!-- you can only list two map engines -->
<!-- Only available since 2.5.16 -->
<dynamic:mapengine id="alternate">
<altlayers>aerial_photo_2001,aerial_photo_2008,aerial_photo_2015</altlayers>
<mapengine>wms1</mapengine>
<mapengine>wms2</mapengine>
</dynamic:mapengine>
</config>
In the above example any configuration item that previously references wms1 or wms2 would now reference redirect, loadbalanced, failover or alternate and operate the same as before with the benefits of the particular function configured. Plus, dynamic map engines can also reference other dynamic map engines, so you can combine load balancing and fail over, for example.