generate-nemo-gym-env

name: generate-nemo-gym-env description: Builds a NeMo Gym (NVIDIA) variant of an RL environment. Use whenever someone asks to scaffold a NeMo Gym Resources Server, port an existing env to NeMo Gym, expose tools as app.post() endpoints with cookie-based sessions, add a post-episode /verify reward grader, or deploy a NeMo Gym env to HF Spaces. NeMo Gym is the right framework when the user wants HTTP+REST with cookie session handling, raw requests-driven rollouts (no SDK client), Ray-based orchestration, or NVIDIA NeMo / TRL training integration with a responses_create_params + ground_truth dataset format. Output is a runnable <env_dir>/nemo_gym/ folder with server.py, pyproject.toml, Dockerfile, configs/<env>.yaml, and rollout.py. Use for prompts like "wrap my env in NeMo Gym", "make a NeMo resources server for X", or "add a post-episode grader to my env".

generate-nemo-gym-env

Build the NeMo Gym variant of an env. NeMo Gym is NVIDIA's RL gym layer, optimized for Ray-based orchestration and post-episode grading. The Python package is nemo_gym (installed via pip install git+https://github.com/NVIDIA-NeMo/Gym).

Concept

NeMo Gym is NVIDIA's RL gym layer for LLM agents. It's built on Ray and ships a FastAPI-based SimpleResourcesServer that exposes one POST /<tool> endpoint per tool, plus the standard /seed_session (cookie-based session bootstrap) and /verify (post-episode grader). Targets docs.nvidia.com/nemo/gym/latest.

When the user has a shared domain module (<domain>.py) and wants a NeMo Gym variant, wrap it. Don't duplicate logic.

Archetypes

Recommended file layout

The user picks the actual paths. The canonical shape:

<env_dir>/nemo_gym/
├── pyproject.toml         # nemo_gym (git+) + e2b-* + fastapi + uvicorn + requests
├── __init__.py
├── Dockerfile             # Ray-aware multi-stage
├── configs/<env>.yaml     # NeMo Gym config (entrypoint, domain, description)
├── server.py              # SimpleResourcesServer subclass with tool endpoints
├── rollout.py             # raw requests + cookie session
└── README.md

Note: NeMo Gym requires Python 3.12+.

Implementation order

1. Server class — server.py

from nemo_gym.base_resources_server import (
    BaseResourcesServerConfig,
    BaseSeedSessionRequest, BaseSeedSessionResponse,
    BaseVerifyRequest, BaseVerifyResponse,
    SimpleResourcesServer,
)
from nemo_gym.server_utils import SESSION_ID_KEY
from fastapi import FastAPI, Request
from pydantic import BaseModel, Field
from typing import Any, Dict

class MyConfig(BaseResourcesServerConfig):
    pass

class GuessReq(BaseModel):
    word: str

class ToolResponse(BaseModel):
    output: str

class MyVerifyRequest(BaseVerifyRequest):
    ground_truth: list = []

class MyResourcesServer(SimpleResourcesServer):
    config: MyConfig
    sessions: Dict[str, Dict[str, Any]] = Field(default_factory=dict)

    def setup_webserver(self) -> FastAPI:
        app = super().setup_webserver()
        app.post("/guess")(self.guess)
        return app

    async def seed_session(self, body: BaseSeedSessionRequest) -> BaseSeedSessionResponse:
        return BaseSeedSessionResponse()

    def _sess(self, request: Request) -> Dict[str, Any]:
        sid = request.session[SESSION_ID_KEY]
        if sid not in self.sessions:
            self.sessions[sid] = {"game": WordleGame(), "step": 0}
        return self.sessions[sid]

    async def guess(self, body: GuessReq, request: Request) -> ToolResponse:
        sess = self._sess(request)
        feedback = sess["game"].guess(body.word)
        sess["step"] += 1
        return ToolResponse(output=feedback)

    async def verify(self, body: MyVerifyRequest) -> BaseVerifyResponse:
        # Compute reward from the response trajectory + ground truth
        expected = ""
        if body.ground_truth and isinstance(body.ground_truth, list):
            expected = body.ground_truth[0].get("expected_output", "")
        reward = 0.0
        for item in body.response.output:
            if hasattr(item, "type") and item.type == "function_call_output":
                if expected and expected in getattr(item, "output", ""):
                    reward = 1.0; break
        return BaseVerifyResponse(**body.model_dump(), reward=reward)

if __name__ == "__main__":
    MyResourcesServer.run_webserver()

Key contracts:

• One endpoint per tool. Register them in setup_webserver(). Pydantic models on the request body become the JSON shape.
• Sessions live in self.sessions keyed by request.session[SESSION_ID_KEY]. Lazy-init on first call. NeMo Gym sets the session cookie on POST /seed_session.
• verify() is the grader. Read body.ground_truth (passed by the trainer) and body.response.output (the trajectory). Return BaseVerifyResponse(**body.model_dump(), reward=...).

2. NeMo Gym config — configs/<name>.yaml

my_env_resources_server:
  resources_servers:
    my_env:
      entrypoint: server.py
      domain: agent
      description: "What this env does"

This is the file the NeMo Gym CLI looks for when launching via ng_run "+config_paths=[configs/my_env.yaml]".

3. Rollout — rollout.py

NeMo Gym has no Python client SDK. The rollout speaks raw HTTP via requests with a Session for cookie persistence:

import requests
session = requests.Session()
session.post(f"{ENV_URL}/seed_session", json={}).raise_for_status()
r = session.post(f"{ENV_URL}/guess", json={"word": "crane"})
result = r.json()["output"]

Tool definitions for the LLM are hardcoded in rollout.py (no introspection endpoint). Mirror the request schemas from server.py exactly.

4. Dockerfile

Multi-stage build. NeMo Gym pulls Ray and a fairly heavy stack — the Docker image is ~1.5GB. The container exposes port 11000 by default. For HF Spaces deployment, override to port 7860 (one-port limit on Spaces).

Validation gates

1. Import — uv run python -c "import os; os.environ.setdefault('E2B_API_KEY','x'); from server import MyResourcesServer" succeeds.
2. Local server — try uv run python server.py. Note: NeMo Gym's run_webserver() initializes a Ray cluster, which fails on shared SLURM / HF cluster nodes (gcs_server can't bind). On those machines, only Docker / HF Space deploy works.
3. Endpoint smoke — when running, curl http://localhost:11000/seed_session -X POST returns 200 and sets a session cookie.
4. Rollout — MAX_TURNS=3 uv run python rollout.py drives end-to-end against the deployed Space.

Common gotchas

• No module named 'anyio' — nemo_gym doesn't pin its full transitive set on every install. Add anyio>=4.0, attrs>=23.0, fastapi>=0.115, uvicorn, requests to your dependencies explicitly.
• Address already in use or gcs_server crash — Ray init failed. Almost always a shared cluster issue. Document this and tell the user to deploy via Space.
• Cookie not set on the rollout — make sure to use requests.Session(), not raw requests.post(). The session cookie is the SID handle.
• /verify returns reward 0 unexpectedly — ground_truth is wrapped in a list. Check body.ground_truth[0].get("expected_output") not body.ground_truth.get(...).
• Hardcoded tool schemas drift — when you change a server endpoint's Pydantic body, manually update the matching tool definition in rollout.py. There's no list_tools().

Reference

• references/architecture.md — Ray orchestration, dataset format with responses_create_params, deployment notes

Official documentation

• NVIDIA-NeMo/Gym — source repo
• NeMo Gym latest docs
• Creating a Resource Server tutorial
• Creating a Training Environment tutorial