UnrealBuildTool and Horde notes

This page makes some notes on mostly undocumented features of UnrealBuildTool and Horde, which is useful if you're trying to configure the environment for running Unreal Engine builds on a build server.

Environment variables

Environment variable name	Environment variable value	Description
UE_HORDE_URL		Set to the Horde URL.
UE_HORDE_TOKEN		Set to the static token for authenticating with Horde.
UnrealBuildTool_Horde__ConnectionMode	Relay	The equivalent of <Horde><ConnectionMode>Relay</ConnectionMode></Horde> in BuildConfiguration.xml, but set via environment variables instead.
UnrealBuildTool_Horde__Cluster	_auto	The equivalent of <Horde><Cluster>_auto</Cluster></Horde> in BuildConfiguration.xml, but set via environment variables instead. This should be set so that Horde knows what type of operating system the agent needs.

Indeed any two-level configuration value inside BuildConfiguration.xml should be able to be set via UnrealBuildTool_CATEGORY__KEY environment variable. We should replace DefaultBuildConfigurationManager with environment variables instead so we can avoid overwriting BuildConfiguration.xml.

Of note, if the environment variable value contains ;, it will be split by the semicolon and instead of a string value, there will be an <Item> element per value added as children to XML.