sglang-setup

SGLang Setup on DGX Station

Deploy an SGLang inference server on DGX Station with validated configuration.

Steps

1. Find the GB300 GPU index. Run:

   nvidia-smi --query-gpu=index,name --format=csv,noheader
   

   Identify the device index for the GB300 (typically device 1). Use this index for --gpus below. Do NOT use --gpus all — mixed coherency will cause CUDA failures.

2. Ask the user which model to serve. If they don't have a preference, suggest:

   • Qwen/Qwen3-8B — small, fast, good for testing
   • Qwen/Qwen3-32B — medium, good balance
   • meta-llama/Llama-3.1-70B-Instruct — large general-purpose

3. Check if the user has an HF_TOKEN. Pass inline with -e HF_TOKEN="...".

4. Deploy the container. Use this validated configuration:

   docker pull lmsysorg/sglang:latest-cu130
   
   docker run -d \
     --name sglang-server \
     --gpus '"device=<GB300_INDEX>"' \
     --ipc host \
     --ulimit memlock=-1 \
     --ulimit stack=67108864 \
     -p 30000:30000 \
     -e HF_TOKEN="<TOKEN>" \
     -v "$HOME/.cache/huggingface/hub:/root/.cache/huggingface/hub" \
     lmsysorg/sglang:latest-cu130 \
     sglang serve --model-path "<MODEL>" \
       --host 0.0.0.0 \
       --port 30000 \
       --context-length 32768 \
       --mem-fraction-static 0.85
   

   Container version: Use lmsysorg/sglang:latest-cu130. The cu130 tag is required for Blackwell SM103 support.

   First launch downloads the model and compiles kernels. This takes extra time — subsequent starts are faster.

5. Wait for the server to be ready. Monitor logs:

   docker logs -f sglang-server
   

6. Test the server:

   curl http://localhost:30000/v1/chat/completions \
     -H "Content-Type: application/json" \
     -d '{
       "model": "<MODEL>",
       "messages": [{"role": "user", "content": "Hello"}],
       "max_tokens": 64
     }'
   

7. Report the result to the user, including:

   • Model loaded and serving on port 30000
   • How to stop: docker stop sglang-server && docker rm sglang-server

Key features

• RadixAttention — automatic KV cache reuse across requests sharing prefixes. On by default, no flag needed. Verify with: docker logs sglang-server 2>&1 | grep "cached-token" | tail -5
• Structured JSON output — use response_format.json_schema in API requests for guaranteed valid JSON.
• Chunked prefill — add --chunked-prefill-size 8192 to break long prefills into chunks, reducing time-to-first-token.

Tuning parameters

Structured output example

curl http://localhost:30000/v1/chat/completions \
  -H "Content-Type: application/json" \
  -d '{
    "model": "<MODEL>",
    "messages": [{"role": "user", "content": "List three programming languages."}],
    "max_tokens": 512,
    "response_format": {
      "type": "json_schema",
      "json_schema": {
        "name": "languages",
        "schema": {
          "type": "object",
          "properties": {
            "languages": {
              "type": "array",
              "items": {
                "type": "object",
                "properties": {
                  "name": {"type": "string"},
                  "primary_use": {"type": "string"}
                },
                "required": ["name", "primary_use"]
              }
            }
          },
          "required": ["languages"]
        }
      }
    }
  }'