Hi,
We’re currently integrating UBA for both C++ and shader compilation in Unreal Engine 5.6, and we’re hitting intermittent failures during shader compilation in cook.
Context
- Unreal Engine version: 5.6
- Horde / UBA agents: 5.7
- UBA enabled for:
- C++ compilation (working reliably)
- Shader compilation (enabled, but unstable)
- Cook duration: ~2 hours
- Issue is intermittent, the same build often succeeds on retry
Configuration
BuildConfiguration.xml
<bAllowUBA>true</bAllowUBA>
<bAllowUBAShaderCompile>true</bAllowUBAShaderCompile>
DefaultEngine.ini
[Uba.Provider.Horde]
Enabled=true
ServerUrl="<https://can-horde-server>..."
Pool=BuildMachine
Cluster=default
MaxCores=2048
[UbaController]
Providers=Uba.Provider.Horde
bReuseProcesses=True
[DevOptions.Shaders]
bAllowCompilingThroughWorkers=True
bAllowAsynchronousShaderCompiling=True
bAllowDistributedShaderCompiling=True
bUseXGEController=False
bUseHordeShaderCompiler=True
MaxShaderJobBatchSize=16
WorkerTimeToLive=600
NumUnusedShaderCompilingThreads=2
Observed Behavior
At the beginning of the cook, UBA + Horde appears to initialize correctly:
LogUbaHorde: UBA/Horde Configuration:
Server: <https://can-horde-server>...
Pool: BuildMachine
We also see:
LogShaderCompilers: Display: Using UBA Controller for shader compilation
LogUbaController: Starting up UBA/Horde connection for session ...
However, later during the cook:
LogUbaController: Shutting down UBA/Horde connectionThen shortly after:
LogUbaController: Starting up UBA/Horde connection for session ...
LogUbaHorde: Warning: Getting Horde server URL failed [Source: Not found]
LogUbaHorde: Error: Failed to create HttpClient for UbaAgent
At this point the cook fails.
What we observed
- The same build often succeeds on retry
- The failure happens after a successful initial Horde session
- The error occurs during re-initialization of UBA/Horde
- C++ compilation via UBA/Horde is stable
- Issue appears only in shader compilation during cook
- Logs suggest the ServerUrl becomes unavailable on second initialization
What we tried
- Fixed INI parsing issues (quotes around ServerUrl)
- Explicit
[UbaController] Providers=...* Enabled
bUseHordeShaderCompiler=True* Increased
WorkerTimeToLive* Enabled
bReuseProcesses=True* Cleared Saved/Intermediate configs
- Verified Horde pool and agents are valid
Suspicions
We suspect one (or a combination) of the following:
- UbaController lifecycle issue in UE 5.6
- Config not reloaded on second initialization
- Version mismatch
- UE 5.6 client vs Horde/UBA agents 5.7
- Shader compilation path being less stable than UBT path
- Session teardown/recreation during long cooks causing loss of Horde config
Questions
- Is UE 5.6 expected to be stable for UBA + Horde shader compilation during cook?
- Are client/agent version mismatches (5.6 vs 5.7) known to cause this kind of issue?
- Should the Horde config be reloaded on every UbaController initialization?
- Is there a known fix or patch for this in 5.6?
- Are there recommended settings to prevent UbaController teardown during long cooks?
Any guidance would be greatly appreciated, especially if this is a known issue or something already fixed in later versions. Happy to provide full logs or test specific changes if needed.
Thanks!
Nathaël Goudreau
PS : Appologies for the duplicate post, I posted in https://forums.unrealengine.com/ before this post.
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