1. CrealyticsEvents
A step closer to an event-driven architecture

2. What we have:
message_bus
• Arbitrarily named topics
• Multiple event types per topic
• event_type explicitly defined as part of the message body
• Which topic should I listen to to get a particular event type?
• No schema validation — can send anything
• No schema versioning — how can we evolve the schema?
• No documentation of topics, event data structure, or data fields
• The message body is JSON

3. What we would like to have:
crealytics_events
• Required field event_type goes away — the topic determines the event
type (1:1 relationship)
• Events are serialized / deserialized to / from Avro
• Event model <=> Avro
• Each topic has its own schema, stored in a schema registry
• Schema evolution and reconciliation is done according to Avro
specifications
• Events are validated against the topic's schema upon production and
consumption
• Schemas and topics are documented with YARD

4. • The crealytics Ruby interface to Apache Kafka
• Abstracts away all concerns associated with
publishing, consuming, serializing, and
deserializing messages
• Supports MRI and JRuby
crealytics_events
v0.0.1

5. External dependencies
• avro-schema-registry
• Implementation of the Confluent Schema Registry API
as a Rails application
• avro-builder
• Ruby DSL to create Avro schemas
• avromatic
• Avromatic generates Ruby models from Avro schemas
and provides utilities to encode and decode them

6. Environment setup
MESOS_ENVIRONMENT=development
KAFKA_BROKERS=kafka1:9092 kafka2:9092
KAFKA_TOPICS=["password-reset-requests"]
KAFKA_SCHEMA_REGISTRY_URL=http://
derp:avro@schema_registry:21000
PORT0=21000

7. Configuration
1. Configure using environment variables
(producer example)

8. Configuration
1. Configure directly
(consumer example)

9. Event models
• Inherit from BaseEvent
• Provides required fields: uuid, time_stamp, and event_source
• Provides method emit for sending events
• Have a unique associated topic inferred from the class name
• For example: CustomerEvent => customer-events
• Include the Avro schemas

10. Avro Schema DSL
• BaseEvent
• A child event (example)

11. Sending events
1. Create an event model
2. Fill in all required fields
3. Call emit

12. Listening for events
(really)

13. What happens when we get
an event?
Remember event handlers during the configuration step?
Q: But what is an event handler?
A: Any object which responds to a method call

14. Wait, but where is Kafka?
Don’t worry about it
(CrealyticsEvents encapsulates all Kafka interaction)

15. Next steps
• Aggregate events, embedding events
• Schema version evolution
• Mapping handlers to event models instead of text
topics
• Improving default decoder

16. Demo

17. Danke!