llm-router/docs

llm‑router‑api#

llm‑router‑api is a lightweight Python library that provides a flexible, extensible proxy for Large Language Model ( LLM) back‑ends. It abstracts the details of multiple model providers (OpenAI‑compatible, Ollama, vLLM, LM Studio, etc.) and offers a unified REST interface with built‑in load‑balancing, health‑checking, and monitoring.

Repository: https://github.com/radlab-dev-group/llm-router

Features#

  • Unified API – One REST surface (/api/...) that proxies calls to any supported LLM back‑end.
  • Provider Selection – Choose a provider per request using pluggable strategies (balanced, weighted, adaptive, first‑available).
  • Prompt Management – System prompts are stored as files and can be dynamically injected with placeholder substitution.
  • Streaming Support – Transparent streaming for both OpenAI‑compatible and Ollama endpoints.
  • Health Checks – Built‑in ping endpoint and Redis‑based provider health monitoring.
  • Prometheus Metrics – Optional instrumentation for request counts, latencies, and error rates.
  • Auto‑Discovery – Endpoints are automatically discovered and instantiated at startup.
  • Extensible – Add new providers, strategies, or custom endpoints with minimal boilerplate.

Installation#

The project uses Python 3.10.6 and a virtualenv‑based workflow.

```shell script

Clone the repository#

git clone https://github.com/radlab-dev-group/llm-router.git cd llm-router

Create a virtual environment#

python3 -m venv venv source venv/bin/activate

Install the package (including optional extras)#

pip install -e .[metrics] # installs Prometheus support

All required third‑party libraries are listed in `requirements.txt` (e.g., Flask, requests, redis, rdl‑ml‑utils, etc.).

---

## Configuration

Configuration is driven primarily by environment variables and a JSON model‑config file.

### Environment Variables

All environment variables are documented in **[ENV_DEFINITIONS.md](./ENV_DEFINITIONS.md)**.

Key categories: **Core** · **Redis** · **Masking & Guardrail** · **Semantic BiEncoder Routing** · **LangChainRAG** · *
*Utils Plugins** · **Authentication**.

---

### Authentication variables

Auth-specific environment variables are documented in **[ENV_DEFINITIONS.md](./ENV_DEFINITIONS.md) → Authentication
section**.

> See full authentication docs: **[AUTHENTICATION.md](AUTHENTICATION.md)**

### Model Configuration

`models-config.json` follows the schema:

```json
{
  "active_models": {
    "openai_models": [
      "gpt-4",
      "gpt-3.5-turbo"
    ],
    "ollama_models": [
      "llama2"
    ]
  },
  "openai_models": {
    "gpt-4": {
      "providers": [
        {
          "id": "openai-gpt4-1",
          "api_host": "https://api.openai.com/v1",
          "api_token": "sk-...",
          "api_type": "openai",
          "input_size": 8192,
          "model_path": ""
        }
      ]
    }
  },
  ...
}

Only the fields required by the router are needed: id, api_host, api_token (optional), api_type, input_size, and optionally model_path.

Configuration Details – see the full schema and a ready‑made example in MODELS_CONFIG.md.

Running the Server#

The entry point is llm_router_api.rest_api. Choose a server backend via the LLM_ROUTER_SERVER_TYPE variable or command‑line flags.

```shell script

Using the built‑in Flask development server (default)#

python -m llm_router_api.rest_api

Production‑grade with Gunicorn (streaming supported)#

python -m llm_router_api.rest_api --gunicorn

Windows‑friendly Waitress server#

python -m llm_router_api.rest_api --waitress ```

The server starts on the host/port defined by LLM_ROUTER_SERVER_HOST and LLM_ROUTER_SERVER_PORT (default 0.0.0.0:8080).

Note: The service must be launched with LLM_ROUTER_MINIMUM=1 (or any truthy value) because it operates in “proxy‑only” mode.

REST API Overview#

All routes are prefixed by LLM_ROUTER_EP_PREFIX (default /api). The list of endpoints—categorized into built‑in, provider‑dependent, and extended endpoints—and a description of the streaming mechanisms can be found at the link: load endpoints overview

Load‑Balancing Strategies#

The router selects a provider for a given model request using the ProviderChooser. The strategy can be chosen via the LLM_ROUTER_BALANCE_STRATEGY variable.

The current list of available strategies, the interface description, and an example extension can be found at the link load balancing strategies

Keep‑Alive Mechanism#

The keep‑alive subsystem periodically pings model endpoints to keep them warm, reducing latency for the first request after idle periods. Configuration is driven by the keep_alive field in the provider definition (see KEEPALIVE.md). Strategies that select providers can register usage with the KeepAliveMonitor, which handles scheduling and background execution.

For details on how to enable and configure keep‑alive, refer to the dedicated documentation: Keep‑Alive Overview

Extending the Router#

Adding a New Provider Type#

  1. Implement ApiTypesI
    Create a class (e.g., MyProviderType) that implements the abstract methods chat_ep, chat_method, completions_ep, and completions_method.
  2. Register in Dispatcher
    Add the class to ApiTypesDispatcher._REGISTRY with a lowercase key.
  3. Update Constants (optional)
    If you need a new balance strategy, extend BalanceStrategies in constants_base.py.

Adding a New Endpoint#

  1. Choose a base class:
    • EndpointWithHttpRequestI for full proxy behaviour (default).
    • PassthroughI if you only need to forward the request unchanged.
    • Directly subclass EndpointI for non‑proxy use cases.
  2. Define REQUIRED_ARGS, OPTIONAL_ARGS, and optionally SYSTEM_PROMPT_NAME.
  3. Implement prepare_payload(self, params) – convert incoming parameters to the payload expected by the downstream model.
  4. (Optional) Set self._prepare_response_function to post‑process the model response.
  5. The endpoint will be auto‑discovered by EndpointAutoLoader at startup.

Prompt Files#

Prompt files live under the directory configured by LLM_ROUTER_PROMPTS_DIR.
File naming convention: <category>/system/<lang>/<prompt-id>.
Placeholders such as ##PLACEHOLDER## can be replaced via self._map_prompt in the endpoint implementation.

Monitoring & Metrics#

When LLM_ROUTER_USE_PROMETHEUS=1 (or true) the router automatically:

  • Exposes a /metrics endpoint (Prometheus format).
  • Tracks HTTP request counts, latency histograms, in‑progress gauges, and error counters.
  • Tracks auth events, rate limits, and key budget usage.
  • Tracks provider-level metrics: calls per provider type, provider latency/errors, load balancing strategy selection, pipeline funnel stages, retry attempts, token usage (input/output), streaming format distribution, and payload conversion counts.

See ROUTING_METRICS.md for the full list of 10 new router metrics with documentation, example PromQL queries, and Grafana dashboard snippets.

You can scrape this endpoint with a Prometheus server or query it manually.

License#

llm-router-api is released under the Apache 2.0. See the LICENSE file in the repository for full terms.

llm-router · docs are generated from the repository by tools/build_docs.py 0.6.8 @ 0576e1e