# Event Brokers

Rasa Core allows you to stream events to a message broker. The event broker emits events into the event queue. It becomes part of the `TrackerStore` which you use when starting an `Agent` or launch `rasa.core.run`.

All events are streamed to the broker as serialised dictionaries every time the tracker updates its state. An example event emitted from the `default` tracker looks like this:

```
{
    "sender_id": "default",
    "timestamp": 1528402837.617099,
    "event": "bot",
    "text": "what your bot said",
    "data": "some data"
}
```

The `event` field takes the event’s `type_name` (for more on event types, check out the [Events](https://legacy-docs-v1.rasa.com/1.3.10/api/events/#events) docs).

Rasa enables three possible broker types:

- [Pika Event Broker](https://legacy-docs-v1.rasa.com/1.3.10/api/event-brokers/#pika-event-broker)
- [Kafka Event Broker](https://legacy-docs-v1.rasa.com/1.3.10/api/event-brokers/#kafka-event-broker)
- [SQL Event Broker](https://legacy-docs-v1.rasa.com/1.3.10/api/event-brokers/#sql-event-broker)

## Pika Event Broker

The example implementation we’re going to show you here uses [Pika](https://pika.readthedocs.io/), the Python client library for [RabbitMQ](https://www.rabbitmq.com/).

### Adding a Pika Event Broker Using the Endpoint Configuration

You can use an endpoint configuration file to instruct Rasa Core to stream all events to your event broker. To do so, add the following section to your endpoint configuration, e.g. `endpoints.yml`:

```
event_broker:
  url: localhost
  username: username
  password: password
  queue: queue
  type: pika
```

Then instruct Rasa Core to use the endpoint configuration and Pika producer by adding `--endpoints <path to your endpoint configuration` as shown in the following example:

```
rasa run -m models --endpoints endpoints.yml
```

### Adding a Pika Event Broker in Python

Here is how you add it using Python code:

```
from rasa.core.event_brokers.pika_producer import PikaProducer
from rasa_platform.core.tracker_store import InMemoryTrackerStore

pika_broker = PikaProducer('localhost',
                            'username',
                            'password',
                            queue='rasa_core_events')

tracker_store = InMemoryTrackerStore(db=db, event_broker=pika_broker)
```

### Implementing a Pika Event Consumer

You need to have a RabbitMQ server running, as well as another application that consumes the events. This consumer needs to implement Pika’s `start_consuming()` method with a `callback` action. Here’s a simple example:

```
import json
import pika

def _callback(self, ch, method, properties, body):
        # Do something useful with your incoming message body here, e.g.
        # saving it to a database
        print('Received event {}'.format(json.loads(body)))

if __name__ == '__main__':
    credentials = pika.PlainCredentials('username', 'password')
    connection = pika.BlockingConnection(
        pika.ConnectionParameters('rabbit', credentials=credentials))
    channel = connection.channel()
    channel.basic_consume(_callback,
                          queue='rasa_core_events',
                          no_ack=True)
    channel.start_consuming()
```

## Kafka Event Broker

It is possible to use [Kafka](https://kafka.apache.org/) as the main broker for your events. In this example, we are going to use the [python-kafka](https://kafka-python.readthedocs.io/en/master/usage.html) library, a Kafka client written in Python.

### Adding a Kafka Event Broker Using the Endpoint Configuration

As for the other brokers, you can use an endpoint configuration file to instruct Rasa Core to stream all events to this event broker. To do it, add the following section to your endpoint configuration.

Pass the `endpoints.yml` file as an argument with `--endpoints <path to your endpoint configuration>` when running Rasa, as shown in the following example:

```
rasa run -m models --endpoints endpoints.yml
```

Using `SASL_PLAINTEXT` protocol the endpoints file must have the following entries:

```
event_broker:
  url: localhost
  sasl_username: username
  sasl_password: password
  topic: topic
  security_protocol: SASL_PLAINTEXT
  type: kafka
```

In the case of using SSL protocol the endpoints file must look like:

```
event_broker:
  url: localhost
  topic: topic
  security_protocol: SSL
  ssl_cafile: CARoot.pem
  ssl_certfile: certificate.pem
  ssl_keyfile: key.pem
  ssl_check_hostname: True
  type: kafka
```

### Adding a Kafka Broker in Python

The code below shows an example of how to instantiate a Kafka producer in your script:

```
from rasa.core.event_brokers.kafka_producer import KafkaProducer
from rasa.core.tracker_store import InMemoryTrackerStore

kafka_broker = KafkaProducer(host='localhost:9092',
                             topic='rasa_core_events')

tracker_store = InMemoryTrackerStore(event_broker=kafka_broker)
```

The host variable can be either a list of broker addresses or a single one. If only one broker address is available, the client will connect to it and request the cluster Metadata.

### Authentication and authorization

Rasa Core’s Kafka producer accepts two types of security protocols - `SASL_PLAINTEXT` and `SSL`.

If clients or brokers in the Kafka cluster are located on different machines, it’s important to use the SSL protocol to ensure encryption of data and client authentication. After generating valid certificates for the brokers and clients, the path to the certificate and key generated for the producer must be provided as arguments, as well as the CA’s root certificate.

### Implementing a Kafka Event Consumer

The parameters used to create a Kafka consumer are the same used on the producer creation, according to the security protocol being used. The following implementation shows an example:

```
from kafka import KafkaConsumer
from json import loads

consumer = KafkaConsumer('rasa_core_events',
                          bootstrap_servers=['localhost:29093'],
                          value_deserializer=lambda m: json.loads(m.decode('utf-8')), 
                          security_protocol='SSL',
                          ssl_check_hostname=False,
                          ssl_cafile='CARoot.pem',
                          ssl_certfile='certificate.pem',
                          ssl_keyfile='key.pem')

for message in consumer:
    print(message.value)
```

## SQL Event Broker

It is possible to use an SQL database as an event broker. Connections to databases are established using [SQLAlchemy](https://www.sqlalchemy.org/), a Python library that can interact with many different types of SQL databases, such as [SQLite](https://sqlite.org/), [PostgreSQL](https://www.postgresql.org/) and more.

### Adding a SQL Event Broker Using the Endpoint Configuration

You can use the endpoint configuration file to instruct Rasa to save all events to your SQL event broker. To do so, add an `event_broker` section to your endpoint configuration, e.g. `endpoints.yml`. For example, a valid SQLite configuration could look like the following:

```
event_broker:
  type: SQL
  dialect: sqlite
  db: events.db
```

PostgreSQL databases can be used as well:

```
event_broker:
  type: SQL
  host: 127.0.0.1
  port: 5432
  dialect: postgresql
  username: myuser
  password: mypassword
  db: mydatabase
```

With this configuration applied, Rasa will create a table called `events` in the database, where all events will be added.