ComfyUI Datadog Monitor

Background extension that adds Datadog APM tracing and CUDA memory tracking to ComfyUI workflow execution. No UI nodes — runs entirely in the background.

Features

Automatic Library Instrumentation: Uses ddtrace.auto to automatically trace HTTP requests, subprocess calls, asyncio operations, logging, and 100+ other Python libraries Workflow Tracing: Each execute_async call is wrapped in a Datadog APM span with prompt ID and job ID tags Per-Node Tracing: Each node execution gets a child span under the workflow span, tagged with class_type, node ID, and optional memory metrics CUDA Memory Snapshots: Captures torch.cuda.memory_stats() before and after each workflow execution (opt-in) CUDA Allocation Tracking: Uses torch.cuda.memory._snapshot() to identify top VRAM allocations with stack traces (opt-in) Per-Node Memory Tracking: Cheap VRAM/RAM snapshots per node using torch.cuda.memory_allocated() and psutil.virtual_memory() (~0.1ms each) OOM Diagnostics: Memory snapshots are captured in a finally block, so they're available even when workflows fail with OOM errors MPS Support: Basic memory tracking for Apple Silicon (allocated + driver memory) Runtime Metrics: Enables ddtrace runtime metrics collection Zero Configuration: Works automatically when installed — no nodes to add Background Only: No UI nodes, runs entirely in the background

What Gets Traced

Automatic (via ddtrace.auto)

The extension enables ddtrace.auto which uses import hooks to automatically instrument supported libraries. For ComfyUI, the most relevant auto-instrumented libraries are:

requests / httpx: Model downloads, API calls to external services asyncio: Async span correlation across the event loop subprocess: Any external process spawns logging: Trace ID injection into log lines for correlation sqlite3: Database operations (if used) aiohttp: Async HTTP operations

Manual (workflow-level)

This extension monkey-patches PromptExecutor.execute_async to wrap each workflow execution in a Datadog span. Each span includes:

workflow.prompt_id: The prompt ID being executed job.id: The job ID from extra_data (if present) memory.pytorch.allocated_bytes.{before,after}: CUDA memory allocated (when PYTORCH_MEMORY_TRACKING=true) memory.pytorch.reserved_bytes.{before,after}: CUDA memory reserved (when PYTORCH_MEMORY_TRACKING=true) memory.pytorch.num_ooms.{before,after}: OOM count from PyTorch stats (when PYTORCH_MEMORY_TRACKING=true) memory.pytorch.cuda_mb.after: Total CUDA allocation in MB (when PYTORCH_MEMORY_TRACKING=true) memory.pytorch.largest_mb.after: Largest single CUDA allocation in MB (when PYTORCH_MEMORY_TRACKING=true) error / error.type: Set on workflow exceptions

Manual (per-node)

Each node execution is wrapped in a child span (comfyui.node.execute) under the workflow span. This is enabled by default and requires no configuration. Each node span includes:

node.id: The unique node ID within the workflow node.class_type: The ComfyUI node type (e.g. KSampler, VAEDecode, CLIPTextEncode) workflow.prompt_id: The prompt ID (same as parent workflow span) node.cached: true if the node result was served from cache node.result: The execution result status (e.g. SUCCESS, FAILURE) error / error.type / error.message: Set on node exceptions memory.vram_allocated_bytes.{before,after}: CUDA VRAM allocated (cheap, ~0.1ms) memory.vram_reserved_bytes.{before,after}: CUDA VRAM reserved (cheap, ~0.1ms) memory.ram_available_bytes.{before,after}: System RAM available (cheap, ~0.1ms)

Trace Structure

comfyui.workflow.execute  (resource: workflow#<prompt_id>)
├── comfyui.node.execute  (resource: CLIPTextEncode)
├── comfyui.node.execute  (resource: KSampler)        ← longest span = bottleneck
├── comfyui.node.execute  (resource: VAEDecode)
├── comfyui.node.execute  (resource: SaveImage)
└── comfyui.node.execute  (resource: LoadCheckpoint)   ← node.cached=true

Installation

1. Install in your ComfyUI custom_nodes directory:

cd custom_nodes
git clone https://github.com/Comfy-Org/comfyui-datadog-monitor
cd comfyui-datadog-monitor
pip install -r requirements.txt

2. Set environment variables:

export DD_ENV=production
export DD_SERVICE=comfyui
export DD_AGENT_HOST=localhost  # Your Datadog agent host

# Optional: enable detailed CUDA memory tracking (workflow-level, expensive)
export PYTORCH_MEMORY_TRACKING=true

3. Restart ComfyUI — tracing starts automatically.

How It Works

When ComfyUI loads this extension:

1. Calls import ddtrace.auto to enable automatic instrumentation of all supported libraries (uses import hooks, so it works even when libraries are already imported)
2. Configures ddtrace with service/env tags and enables runtime metrics
3. If PYTORCH_MEMORY_TRACKING=true, enables torch.cuda.memory._record_memory_history() for detailed allocation tracking
4. Monkey-patches PromptExecutor.execute_async to wrap workflow execution in a Datadog span with memory snapshots
5. Monkey-patches the module-level execution.execute() function to wrap each node execution in a child span with cheap memory snapshots

Child span nesting is handled automatically by ddtrace's context propagation — no explicit parent linking is needed.

Environment Variables

Variable	Default	Description
DD_ENV	production	Datadog environment tag
DD_SERVICE	comfyui	Datadog service name
DD_AGENT_HOST	localhost	Datadog agent hostname
PYTORCH_MEMORY_TRACKING	false	Enable detailed CUDA memory snapshots and allocation tracking (workflow-level, uses expensive memory_stats() and memory._snapshot())
NODE_TRACING_ENABLED	true	Enable per-node child spans under the workflow span
NODE_MEMORY_TRACKING	true	Enable cheap VRAM/RAM snapshots on each node span (only applies when NODE_TRACING_ENABLED=true)
DD_PROFILING_ENABLED	true	Enable ddtrace CPU/memory profiler (~2% CPU overhead)

Standard ddtrace environment variables (e.g. DD_TRACE_SAMPLE_RATE, DD_LOGS_INJECTION, DD_TRACE_<LIBRARY>_ENABLED) are also respected. You can disable auto-instrumentation for specific libraries with e.g. DD_TRACE_REQUESTS_ENABLED=false.

OOM Debugging

When PYTORCH_MEMORY_TRACKING=true, the extension captures memory state in a finally block — so even when a workflow fails with a CUDA OOM error, you get:

• Memory stats at the point of failure (allocated, reserved, OOM count)
• Top CUDA VRAM allocations with stack traces showing where memory was allocated

Look for spans with error=True and error.type=OutOfMemoryError in Datadog APM.

Performance Impact

Auto-instrumentation overhead: Negligible per-call wrapping of library functions. For a GPU-bound ML inference workload, this is immeasurable. Workflow tracing: One additional span per workflow execution, plus child spans from auto-instrumented libraries. Per-node tracing (enabled by default): One span per node execution. Uses torch.cuda.memory_allocated() and psutil.virtual_memory() for memory snapshots — both are ~0.1ms with no GPU synchronization. For a typical 10-node workflow, this adds ~2ms total overhead. Detailed memory tracking (opt-in): torch.cuda.memory_stats() (~5-10ms) and torch.cuda.memory._snapshot() (~50-200ms) are called twice per workflow (before/after). These are O(segments) operations on the CUDA allocator's internal data — no Python object scanning. ⏱ CPU profiling (enabled by default): Sampling-based, ~2% CPU overhead. No impact on GPU/CUDA kernel execution. Disable with DD_PROFILING_ENABLED=false.

Troubleshooting

DDTrace fails to start: Check if Datadog agent is running and accessible at DD_AGENT_HOST.

No data in Datadog: Verify DD_AGENT_HOST points to your Datadog agent.

Import error: Make sure ddtrace is installed: pip install ddtrace

No memory metrics: Set PYTORCH_MEMORY_TRACKING=true and ensure CUDA is available. For per-node memory metrics, ensure NODE_MEMORY_TRACKING=true (default).

Too many spans: If per-node spans create too much volume, disable with NODE_TRACING_ENABLED=false. Or keep tracing but disable memory snapshots with NODE_MEMORY_TRACKING=false.

No per-node spans: Verify NODE_TRACING_ENABLED is not set to false. Check startup logs for "Per-node execution instrumented".

License

MIT