# `LlmComposer.ProviderRouter.Simple`
[🔗](https://github.com/doofinder/llm_composer/blob/master/lib/llm_composer/provider_router/simple.ex#L1)

Simple provider router that implements exponential backoff for failed providers.

This router blocks providers that encounter specific types of errors for a configurable
backoff period. The backoff duration increases exponentially with each consecutive failure,
helping to avoid overwhelming failing services while allowing for automatic recovery.

## Configuration

Configuration is done via application environment:

```elixir
config :llm_composer, :provider_router,
  min_backoff_ms: 1_000,                    # 1 second minimum backoff (default)
  max_backoff_ms: :timer.minutes(5),        # 5 minutes maximum backoff (default)
  cache_mod: LlmComposer.Cache.Ets,         # Cache module to use (default)
  cache_opts: [                             # Cache options (default shown below)
    name: LlmComposer.ProviderRouter.Simple,
    table_name: :llm_composer_provider_blocks
  ],
  name: LlmComposer.ProviderRouter.Simple   # Router instance name (default)
```

## Backoff Strategy

The router uses exponential backoff with the following formula:
```
backoff_ms = min(max_backoff_ms, min_backoff_ms * 2^(failure_count - 1))
```

Examples with default settings:
- 1st failure: 1 second
- 2nd failure: 2 seconds
- 3rd failure: 4 seconds
- 4th failure: 8 seconds
- 5th failure: 16 seconds
- ...continuing until max_backoff_ms (5 minutes)

## Behavior

- **Success**: Provider is unblocked and failure count is reset
- **Failure**: Provider is blocked for exponential backoff period
- **Blocking**: Blocked providers are skipped during provider selection
- **Recovery**: Providers automatically become available after backoff period expires
- **Persistence**: Blocking state persists across application restarts (stored in ETS with long TTL)

# `on_provider_failure`

Handle provider failure and determine if the provider should be blocked.

The provider will be blocked for the configured backoff duration.

# `on_provider_success`

Handle provider success by unblocking the provider and resetting its failure count.

This removes any blocking state for the provider, allowing it to be used immediately
for future requests.

# `select_provider`

Selects an eligible provider from the given list.

This implementation iterates through the providers and returns the first one
that is not currently blocked by the circuit breaker.

# `start_link`

Initialize the ETS table for storing provider blocking state.

---

*Consult [api-reference.md](api-reference.md) for complete listing*