litellm-mirror/docs/my-website/docs/tutorials/fallbacks.md

# Using completion() with Fallbacks for Reliability

This tutorial demonstrates how to employ the `completion()` function with model fallbacks to ensure reliability. LLM APIs can be unstable, completion() with fallbacks ensures you'll always get a response from your calls

## Usage 
To use fallback models with `completion()`, specify a list of models in the `fallbacks` parameter. 

The `fallbacks` list should include the primary model you want to use, followed by additional models that can be used as backups in case the primary model fails to provide a response.

```python
response = completion(model="bad-model", fallbacks=["gpt-3.5-turbo" "command-nightly"], messages=messages)
```

## How does `completion_with_fallbacks()` work

The `completion_with_fallbacks()` function attempts a completion call using the primary model specified as `model` in `completion(model=model)`. If the primary model fails or encounters an error, it automatically tries the `fallbacks` models in the specified order. This ensures a response even if the primary model is unavailable.

### Output from calls
```
Completion with 'bad-model': got exception Unable to map your input to a model. Check your input - {'model': 'bad-model'



completion call gpt-3.5-turbo
{
  "id": "chatcmpl-7qTmVRuO3m3gIBg4aTmAumV1TmQhB",
  "object": "chat.completion",
  "created": 1692741891,
  "model": "gpt-3.5-turbo-0613",
  "choices": [
    {
      "index": 0,
      "message": {
        "role": "assistant",
        "content": "I apologize, but as an AI, I do not have the capability to provide real-time weather updates. However, you can easily check the current weather in San Francisco by using a search engine or checking a weather website or app."
      },
      "finish_reason": "stop"
    }
  ],
  "usage": {
    "prompt_tokens": 16,
    "completion_tokens": 46,
    "total_tokens": 62
  }
}

```

### Key components of Model Fallbacks implementation:
* Looping through `fallbacks`
* Cool-Downs for rate-limited models

#### Looping through `fallbacks`
Allow `45seconds` for each request. In the 45s this function tries calling the primary model set as `model`. If model fails it loops through the backup `fallbacks` models and attempts to get a response in the allocated `45s` time set here: 
```python
while response == None and time.time() - start_time < 45:
        for model in fallbacks:
```

#### Cool-Downs for rate-limited models
If a model API call leads to an error - allow it to cooldown for `60s`
```python
except Exception as e:
  print(f"got exception {e} for model {model}")
  rate_limited_models.add(model)
  model_expiration_times[model] = (
      time.time() + 60
  )  # cool down this selected model
  pass
```

Before making an LLM API call we check if the selected model is in `rate_limited_models`, if so skip making the API call
```python
if (
  model in rate_limited_models
):  # check if model is currently cooling down
  if (
      model_expiration_times.get(model)
      and time.time() >= model_expiration_times[model]
  ):
      rate_limited_models.remove(
          model
      )  # check if it's been 60s of cool down and remove model
  else:
      continue  # skip model

```

#### Full code of completion with fallbacks()
```python

    response = None
    rate_limited_models = set()
    model_expiration_times = {}
    start_time = time.time()
    fallbacks = [kwargs["model"]] + kwargs["fallbacks"]
    del kwargs["fallbacks"]  # remove fallbacks so it's not recursive

    while response == None and time.time() - start_time < 45:
        for model in fallbacks:
            # loop thru all models
            try:
                if (
                    model in rate_limited_models
                ):  # check if model is currently cooling down
                    if (
                        model_expiration_times.get(model)
                        and time.time() >= model_expiration_times[model]
                    ):
                        rate_limited_models.remove(
                            model
                        )  # check if it's been 60s of cool down and remove model
                    else:
                        continue  # skip model

                # delete model from kwargs if it exists
                if kwargs.get("model"):
                    del kwargs["model"]

                print("making completion call", model)
                response = litellm.completion(**kwargs, model=model)

                if response != None:
                    return response

            except Exception as e:
                print(f"got exception {e} for model {model}")
                rate_limited_models.add(model)
                model_expiration_times[model] = (
                    time.time() + 60
                )  # cool down this selected model
                pass
    return response
```