ComfyUI Modal-Sync

ComfyUI Modal-Sync is a ComfyUI custom node extension that lets you mark individual nodes for remote execution. The frontend stores a per-node is_modal_remote flag in workflow metadata, the backend rewrites those nodes into a Modal proxy before queueing, and the proxy forwards execution payloads through a serialization layer that is safe for tensors and plain JSON values.

What is implemented

• A frontend extension in web/modal_toggle.js that injects a Run on Modal toggle into every non-internal node, draws a blue border around remote nodes, and submits queued prompts to /modal/queue_prompt.
• A backend route in api_intercept.py that reads the workflow snapshot from extra_pnginfo.workflow, identifies remote-marked nodes, syncs referenced assets, and rewrites each remote node into a signature-preserving Modal proxy node.
• A dynamic proxy registry in modal_executor_node.py that mirrors the original node’s output count and output types so ComfyUI validation still succeeds after rewrite.
• A content-addressable sync engine in sync_engine.py that mirrors model files and a zipped custom_nodes/ bundle into storage keyed by SHA256.
• A remote runtime skeleton in remote/modal_app.py that supports local fallback execution for tests and can call into Modal when the SDK is available.

Repository layout

.
├── __init__.py
├── api_intercept.py
├── modal_executor_node.py
├── remote/
│   ├── __init__.py
│   └── modal_app.py
├── serialization.py
├── settings.py
├── sync_engine.py
├── tests/
└── web/
    └── modal_toggle.js

Runtime behavior

1. Queueing a prompt posts to /modal/queue_prompt.
2. The route loads the workflow metadata from extra_data.extra_pnginfo.workflow.
3. Nodes with properties.is_modal_remote = true are replaced with a generated ModalUniversalExecutor_<hash> node id.
4. File-like widget inputs ending in .safetensors, .ckpt, .pt, or .vae are resolved to local files and mirrored into storage.
5. The executor serializes tensors with safetensors, forwards the payload to the remote runtime, and deserializes the returned outputs back into ComfyUI values.

Configuration

These environment variables are supported:

• COMFY_MODAL_ROUTE_PATH: Override the queue endpoint. Default: /modal/queue_prompt.
• COMFY_MODAL_MARKER_PROPERTY: Override the workflow property used to mark nodes. Default: is_modal_remote.
• COMFY_MODAL_LOCAL_STORAGE_ROOT: Local mirror root used for sync tests and dry runs. Default: /tmp/comfyui-modal-sync-storage.
• COMFY_MODAL_CUSTOM_NODES_DIR: Override the custom_nodes directory to bundle and mirror.
• COMFY_MODAL_EXECUTION_MODE: Set to local for in-process fallback execution. Default: local.
• COMFY_MODAL_APP_NAME and COMFY_MODAL_VOLUME_NAME: Override Modal app and volume naming.

Development

• Run tests with uv run pytest.
• The project includes a minimal pyproject.toml so pytest discovery is consistent under uv.

Current limitations

• The graph rewrite is per-node, not whole-subgraph partitioning. Remote-to-remote chains will currently round-trip through the local executor boundary between nodes.
• The default sync backend is a local mirror used for development and tests. The Modal runtime entrypoint is present, but real cloud execution still depends on a working Modal SDK environment.
• Non-JSON, non-bytes, non-tensor values cannot be serialized across the remote boundary yet. Unsupported types raise immediately instead of silently degrading.