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 launching rasa.core.run.

All events are streamed to the broker as serialized 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 docs).

Rasa enables three possible broker types:

• Pika Event Broker
• Kafka Event Broker
• SQL Event Broker

Pika Event Broker

The example implementation we’re going to show you here uses Pika, the Python client library for RabbitMQ.

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 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.brokers.pika import PikaEventBroker
from rasa.core.tracker_store import InMemoryTrackerStore

pika_broker = PikaEventBroker('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__':

# RabbitMQ credentials with username and password
    credentials = pika.PlainCredentials('username', 'password')

# Pika connection to the RabbitMQ host - typically 'rabbit' in a
    # docker environment, or 'localhost' in a local environment
    connection = pika.BlockingConnection(
        pika.ConnectionParameters('rabbit', credentials=credentials))

# start consumption of channel
    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 as the main broker for your events. In this example, we are going to use the python-kafka library, a Kafka client written in Python.

Note: In order to use the Kafka event broker, rasa has to be installed with the kafka option:

$ pip install rasa[kafka]

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 that, 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 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.brokers.kafka import KafkaEventBroker
from rasa.core.tracker_store import InMemoryTrackerStore

kafka_broker = KafkaEventBroker(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. Therefore, the remaining brokers in the cluster can be discovered automatically through the data served by the first connected broker.

To pass more than one broker address as an argument, they must be passed in a list of strings. e.g.:

kafka_broker = KafkaEventBroker(host=['kafka_broker_1:9092',\
                                      'kafka_broker_2:2030',\
                                      'kafka_broker_3:9092'],
                                topic='rasa_core_events')

Authentication and Authorization

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

For the development environment, or if the brokers servers and clients are located on the same machine, you can use simple authentication with SASL_PLAINTEXT. By using this protocol, the credentials and messages exchanged between the clients and servers will be sent in plaintext. Thus, this is not the most secure approach, but since it’s simple to configure, it is useful for simple cluster configurations.

SASL_PLAINTEXT protocol requires the setup of the username and password previously configured in the broker server.

kafka_broker = KafkaEventBroker(host='kafka_broker:9092',
                                sasl_plain_username='kafka_username',
                                sasl_plain_password='kafka_password',
                                security_protocol='SASL_PLAINTEXT',
                                topic='rasa_core_events')

If the clients or the brokers in the Kafka cluster are located on different machines, it’s important to use SSL protocol to ensure the encryption of data and client authentication. After generating valid certificates for the brokers and the 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.

kafka_broker = KafkaEventBroker(host='kafka_broker:9092',
                                ssl_cafile='CARoot.pem',
                                ssl_certfile='certificate.pem',
                                ssl_keyfile='key.pem',
                                ssl_check_hostname=True,
                                security_protocol='SSL',
                                topic='rasa_core_events')

If the ssl_check_hostname parameter is enabled, the clients will verify if the broker’s hostname matches the certificate. It’s used on the client’s connections and inter-broker connections to prevent man-in-the-middle attacks.

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, a Python library that can interact with many different types of SQL databases, such as SQLite, PostgreSQL and more. The default Rasa installation allows connections to SQLite and PostgreSQL databases. To see other options, please see the SQLAlchemy documentation on SQL dialects.

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 as follows:

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

PostgreSQL databases can also be used:

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.

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