> ## Documentation Index
> Fetch the complete documentation index at: https://iii.dev/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Adapters

> Pluggable backends for iii workers — swap between in-memory, file-based, Redis, and RabbitMQ without changing your application code.

Each iii worker that needs persistence or distribution uses an **adapter** — a pluggable backend that implements a fixed interface. Swap adapters in `iii-config.yaml` without touching application code.

## Pattern

```yaml theme={"theme":{"light":"catppuccin-latte","dark":"dark-plus"}}
workers:
  - name: iii-queue
    config:
      adapter:
        name: redis
        config:
          redis_url: ${REDIS_URL:redis://localhost:6379}
```

Every adapter entry has two fields:

* `name` — the adapter short name
* `config` — adapter-specific config (omit if not needed)

## Adapter Reference

### Queue

| Adapter  | Name       | External dependency |
| -------- | ---------- | ------------------- |
| Built-in | `builtin`  | None                |
| Redis    | `redis`    | Redis               |
| RabbitMQ | `rabbitmq` | RabbitMQ            |

#### `builtin`

Default. In-process only with retries and DLQ — does not share messages across engine instances.

```yaml theme={"theme":{"light":"catppuccin-latte","dark":"dark-plus"}}
adapter:
  name: builtin
```

#### `redis`

```yaml theme={"theme":{"light":"catppuccin-latte","dark":"dark-plus"}}
adapter:
  name: redis
  config:
    redis_url: ${REDIS_URL:redis://localhost:6379}
```

#### `rabbitmq`

```yaml theme={"theme":{"light":"catppuccin-latte","dark":"dark-plus"}}
adapter:
  name: rabbitmq
  config:
    amqp_url: ${RABBITMQ_URL:amqp://localhost:5672}
    max_attempts: 3
    prefetch_count: 10
    queue_mode: standard   # standard | fifo
```

<Info>
  For retry behavior, dead-letter queues, and full config reference, see the [Queue worker](../workers/iii-queue).
</Info>

***

### State

| Adapter  | Name     | External dependency |
| -------- | -------- | ------------------- |
| KV Store | `kv`     | None                |
| Redis    | `redis`  | Redis               |
| Bridge   | `bridge` | Remote iii Engine   |

#### `kv`

Default. Supports in-memory or file-based persistence.

```yaml theme={"theme":{"light":"catppuccin-latte","dark":"dark-plus"}}
adapter:
  name: kv
  config:
    store_method: file_based   # in_memory | file_based
    file_path: ./data/state
    save_interval_ms: 5000
```

#### `redis`

```yaml theme={"theme":{"light":"catppuccin-latte","dark":"dark-plus"}}
adapter:
  name: redis
  config:
    redis_url: ${REDIS_URL:redis://localhost:6379}
```

#### `bridge`

Forwards state operations to a remote iii Engine.

```yaml theme={"theme":{"light":"catppuccin-latte","dark":"dark-plus"}}
adapter:
  name: bridge
```

***

### Stream

| Adapter  | Name    | External dependency |
| -------- | ------- | ------------------- |
| KV Store | `kv`    | None                |
| Redis    | `redis` | Redis               |

#### `kv`

Default. In-process only.

```yaml theme={"theme":{"light":"catppuccin-latte","dark":"dark-plus"}}
adapter:
  name: kv
  config:
    store_method: file_based   # in_memory | file_based
    file_path: ./data/stream_store
    save_interval_ms: 5000
```

#### `redis`

```yaml theme={"theme":{"light":"catppuccin-latte","dark":"dark-plus"}}
adapter:
  name: redis
  config:
    redis_url: ${REDIS_URL:redis://localhost:6379}
```

***

### Cron

| Adapter    | Name    | External dependency |
| ---------- | ------- | ------------------- |
| KV Cron    | `kv`    | None                |
| Redis Cron | `redis` | Redis               |

#### `kv`

Default. Process-local locks — jobs may run on every instance in multi-instance deployments.

```yaml theme={"theme":{"light":"catppuccin-latte","dark":"dark-plus"}}
adapter:
  name: kv
```

#### `redis`

Distributed locking via Redis — ensures each job runs only once across all instances.

```yaml theme={"theme":{"light":"catppuccin-latte","dark":"dark-plus"}}
adapter:
  name: redis
  config:
    redis_url: ${REDIS_URL:redis://localhost:6379}
```

***

### PubSub

| Adapter | Name    | External dependency |
| ------- | ------- | ------------------- |
| Local   | `local` | None                |
| Redis   | `redis` | Redis               |

#### `local`

Default. In-process broadcast — subscribers must be in the same engine process.

```yaml theme={"theme":{"light":"catppuccin-latte","dark":"dark-plus"}}
adapter:
  name: local
```

#### `redis`

```yaml theme={"theme":{"light":"catppuccin-latte","dark":"dark-plus"}}
adapter:
  name: redis
  config:
    redis_url: ${REDIS_URL:redis://localhost:6379}
```

***

## Choosing an Adapter

|            | Single instance       | Multi-instance                  |
| ---------- | --------------------- | ------------------------------- |
| **Queue**  | BuiltinQueueAdapter   | RedisAdapter or RabbitMQAdapter |
| **State**  | KvStore (file\_based) | RedisAdapter                    |
| **Stream** | KvStore               | RedisAdapter                    |
| **Cron**   | KvCronAdapter         | RedisCronAdapter                |
| **PubSub** | LocalAdapter          | RedisAdapter                    |

<Info title="Environment variables">
  Use `${VAR:default}` syntax in `iii-config.yaml` to switch adapters per environment without changing the file:

  ```yaml theme={"theme":{"light":"catppuccin-latte","dark":"dark-plus"}}
  redis_url: ${REDIS_URL:redis://localhost:6379}
  ```
</Info>