modal-serverless-gpu✓ Pass

SKILL.md Content

---
name: modal-serverless-gpu
description: Serverless GPU cloud platform for running ML workloads. Use when you need on-demand GPU access without infrastructure management, deploying ML models as APIs, or running batch jobs with automatic scaling.
version: 1.0.0
author: Orchestra Research
license: MIT
dependencies: [modal>=0.64.0]
platforms: [linux, macos, windows]
metadata:
  hermes:
    tags: [Infrastructure, Serverless, GPU, Cloud, Deployment, Modal]

---

# Modal Serverless GPU

Comprehensive guide to running ML workloads on Modal's serverless GPU cloud platform.

## When to use Modal

**Use Modal when:**
- Running GPU-intensive ML workloads without managing infrastructure
- Deploying ML models as auto-scaling APIs
- Running batch processing jobs (training, inference, data processing)
- Need pay-per-second GPU pricing without idle costs
- Prototyping ML applications quickly
- Running scheduled jobs (cron-like workloads)

**Key features:**
- **Serverless GPUs**: T4, L4, A10G, L40S, A100, H100, H200, B200 on-demand
- **Python-native**: Define infrastructure in Python code, no YAML
- **Auto-scaling**: Scale to zero, scale to 100+ GPUs instantly
- **Sub-second cold starts**: Rust-based infrastructure for fast container launches
- **Container caching**: Image layers cached for rapid iteration
- **Web endpoints**: Deploy functions as REST APIs with zero-downtime updates

**Use alternatives instead:**
- **RunPod**: For longer-running pods with persistent state
- **Lambda Labs**: For reserved GPU instances
- **SkyPilot**: For multi-cloud orchestration and cost optimization
- **Kubernetes**: For complex multi-service architectures

## Quick start

### Installation

```bash
pip install modal
modal setup  # Opens browser for authentication
```

### Hello World with GPU

```python
import modal

app = modal.App("hello-gpu")

@app.function(gpu="T4")
def gpu_info():
    import subprocess
    return subprocess.run(["nvidia-smi"], capture_output=True, text=True).stdout

@app.local_entrypoint()
def main():
    print(gpu_info.remote())
```

Run: `modal run hello_gpu.py`

### Basic inference endpoint

```python
import modal

app = modal.App("text-generation")
image = modal.Image.debian_slim().pip_install("transformers", "torch", "accelerate")

@app.cls(gpu="A10G", image=image)
class TextGenerator:
    @modal.enter()
    def load_model(self):
        from transformers import pipeline
        self.pipe = pipeline("text-generation", model="gpt2", device=0)

    @modal.method()
    def generate(self, prompt: str) -> str:
        return self.pipe(prompt, max_length=100)[0]["generated_text"]

@app.local_entrypoint()
def main():
    print(TextGenerator().generate.remote("Hello, world"))
```

## Core concepts

### Key components

| Component | Purpose |
|-----------|---------|
| `App` | Container for functions and resources |
| `Function` | Serverless function with compute specs |
| `Cls` | Class-based functions with lifecycle hooks |
| `Image` | Container image definition |
| `Volume` | Persistent storage for models/data |
| `Secret` | Secure credential storage |

### Execution modes

| Command | Description |
|---------|-------------|
| `modal run script.py` | Execute and exit |
| `modal serve script.py` | Development with live reload |
| `modal deploy script.py` | Persistent cloud deployment |

## GPU configuration

### Available GPUs

| GPU | VRAM | Best For |
|-----|------|----------|
| `T4` | 16GB | Budget inference, small models |
| `L4` | 24GB | Inference, Ada Lovelace arch |
| `A10G` | 24GB | Training/inference, 3.3x faster than T4 |
| `L40S` | 48GB | Recommended for inference (best cost/perf) |
| `A100-40GB` | 40GB | Large model training |
| `A100-80GB` | 80GB | Very large models |
| `H100` | 80GB | Fastest, FP8 + Transformer Engine |
| `H200` | 141GB | Auto-upgrade from H100, 4.8TB/s bandwidth |
| `B200` | Latest | Blackwell architecture |

### GPU specification patterns

```python
# Single GPU
@app.function(gpu="A100")

# Specific memory variant
@app.function(gpu="A100-80GB")

# Multiple GPUs (up to 8)
@app.function(gpu="H100:4")

# GPU with fallbacks
@app.function(gpu=["H100", "A100", "L40S"])

# Any available GPU
@app.function(gpu="any")
```

## Container images

```python
# Basic image with pip
image = modal.Image.debian_slim(python_version="3.11").pip_install(
    "torch==2.1.0", "transformers==4.36.0", "accelerate"
)

# From CUDA base
image = modal.Image.from_registry(
    "nvidia/cuda:12.1.0-cudnn8-devel-ubuntu22.04",
    add_python="3.11"
).pip_install("torch", "transformers")

# With system packages
image = modal.Image.debian_slim().apt_install("git", "ffmpeg").pip_install("whisper")
```

## Persistent storage

```python
volume = modal.Volume.from_name("model-cache", create_if_missing=True)

@app.function(gpu="A10G", volumes={"/models": volume})
def load_model():
    import os
    model_path = "/models/llama-7b"
    if not os.path.exists(model_path):
        model = download_model()
        model.save_pretrained(model_path)
        volume.commit()  # Persist changes
    return load_from_path(model_path)
```

## Web endpoints

### FastAPI endpoint decorator

```python
@app.function()
@modal.fastapi_endpoint(method="POST")
def predict(text: str) -> dict:
    return {"result": model.predict(text)}
```

### Full ASGI app

```python
from fastapi import FastAPI
web_app = FastAPI()

@web_app.post("/predict")
async def predict(text: str):
    return {"result": await model.predict.remote.aio(text)}

@app.function()
@modal.asgi_app()
def fastapi_app():
    return web_app
```

### Web endpoint types

| Decorator | Use Case |
|-----------|----------|
| `@modal.fastapi_endpoint()` | Simple function → API |
| `@modal.asgi_app()` | Full FastAPI/Starlette apps |
| `@modal.wsgi_app()` | Django/Flask apps |
| `@modal.web_server(port)` | Arbitrary HTTP servers |

## Dynamic batching

```python
@app.function()
@modal.batched(max_batch_size=32, wait_ms=100)
async def batch_predict(inputs: list[str]) -> list[dict]:
    # Inputs automatically batched
    return model.batch_predict(inputs)
```

## Secrets management

```bash
# Create secret
modal secret create huggingface HF_TOKEN=hf_xxx
```

```python
@app.function(secrets=[modal.Secret.from_name("huggingface")])
def download_model():
    import os
    token = os.environ["HF_TOKEN"]
```

## Scheduling

```python
@app.function(schedule=modal.Cron("0 0 * * *"))  # Daily midnight
def daily_job():
    pass

@app.function(schedule=modal.Period(hours=1))
def hourly_job():
    pass
```

## Performance optimization

### Cold start mitigation

```python
@app.function(
    container_idle_timeout=300,  # Keep warm 5 min
    allow_concurrent_inputs=10,  # Handle concurrent requests
)
def inference():
    pass
```

### Model loading best practices

```python
@app.cls(gpu="A100")
class Model:
    @modal.enter()  # Run once at container start
    def load(self):
        self.model = load_model()  # Load during warm-up

    @modal.method()
    def predict(self, x):
        return self.model(x)
```

## Parallel processing

```python
@app.function()
def process_item(item):
    return expensive_computation(item)

@app.function()
def run_parallel():
    items = list(range(1000))
    # Fan out to parallel containers
    results = list(process_item.map(items))
    return results
```

## Common configuration

```python
@app.function(
    gpu="A100",
    memory=32768,              # 32GB RAM
    cpu=4,                     # 4 CPU cores
    timeout=3600,              # 1 hour max
    container_idle_timeout=120,# Keep warm 2 min
    retries=3,                 # Retry on failure
    concurrency_limit=10,      # Max concurrent containers
)
def my_function():
    pass
```

## Debugging

```python
# Test locally
if __name__ == "__main__":
    result = my_function.local()

# View logs
# modal app logs my-app
```

## Common issues

| Issue | Solution |
|-------|----------|
| Cold start latency | Increase `container_idle_timeout`, use `@modal.enter()` |
| GPU OOM | Use larger GPU (`A100-80GB`), enable gradient checkpointing |
| Image build fails | Pin dependency versions, check CUDA compatibility |
| Timeout errors | Increase `timeout`, add checkpointing |

## References

- **[Advanced Usage](references/advanced-usage.md)** - Multi-GPU, distributed training, cost optimization
- **[Troubleshooting](references/troubleshooting.md)** - Common issues and solutions

## Resources

- **Documentation**: https://modal.com/docs
- **Examples**: https://github.com/modal-labs/modal-examples
- **Pricing**: https://modal.com/pricing
- **Discord**: https://discord.gg/modal

License

Declared license: MIT

MIT License

Copyright (c) 2025 Orchestra Research

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

View the license in the source repository — the version published there is authoritative.