FASTBuild with Unreal Engine 4 setup

So you want to build Unreal Engine 4 with FASTBuild… Or maybe you don’t want to pay for Incredibuild but rebuilding Unreal in 45 minutes doesn’t seem promising. You are in the right spot. Here were our steps to building UE4 with FASTBuild on Windows.

1. Download FASTBuild from here, the latest x64 Windows version most likely. Move the extracted folder to the Engine/Extras folder in Unreal.
2. Download FASTBuild.cs from here and place under Engine/Source/Programs/UnrealBuildTool/System/. Either add it to the UnrealBuildTool project yourself or regenerate the projects.
3. Modify the ActionGraph.cs file, specifically the ExecuteActions method, to call FASTBuild.ExecuteActions like so:
   
   For Unreal Engine before 4.15, it looked more like this:
   In both cases, you can of course also add a bAllowFastBuild bool to BuildConfiguration.cs to control who attempts to use FASTBuild.
4. Rebuild UnrealBuildTool from Visual Studio.
5. Build a smaller project, like say ShaderCompileWorker to test it out! It should use FASTBuild, but it won’t build across the network or use the cache without a little bit more setup.

Next you’ll want to set up caching and distribution, as that’s where you’ll actually see the benefits of using FASTBuild!