Have your cake and eat it
 An introduction to event-driven architecture @RyanTownsend December 13th, 2017 Code Europe, Wrocław

Ryan Townsend Chief Technology Officer,

No content

✋ I know what event-driven architecture means ✋ I know what event sourcing means ✋ I know what CQRS means show of hands

1. What is event-driven architecture? 2. Why is it important? 3. What’s possible? 4. Are there any downsides? 5. How can we use it today? agenda

“Data is the new oil”

“Data is the new oil.” Clive Humby, Architect of Tesco’s Clubcard, 2006 “Personal data is the new oil of the internet” Meglena Kuneva, European Consumer Commissioner, 2009 “Data is the new oil” Ann Winblad, Senior Partner at Hummer-Winblad, 2012 “Data is the new oil. The companies that will win are using math.”
 Kevin Plank, founder and CEO of Under Armour, 2016 “Data is the new oil.”
 Richard Titus, CEO AND, 2010 “We’re able to view just everything that they do. [...] Data is the new oil.”
 Bill Diggins, CEO Diggit, 2012 “I want you to think about data as the next natural resource.”
 Virginia Rometty, IBM CEO, 2013 “Information is the oil of the 21st century”
 Peter Sondergaard, SVP Gartner, 2011 “Data is going to be the natural resource for this industrial revolution.” Abhishek Mehta, CEO Tresata, 2013 Source: https://www.quora.com/Who-should-get-credit-for-the-quote-data-is-the-new-oil

Traditional relational data is a snapshot of ‘now’

Life and data are fluid

They are the product of events

• Financial transactions • Sports tournaments • Order shipments • Election polls • Flight arrivals, departures • Hotel check-in & check-out • Restaurant table availability • Read receipts for messages all kinds of events

And there are knock-on actions

Does the flap of a butterfly's wings in Brazil set off a tornado in Texas? butterfly effect

Can we model our applications closer to real-life?

• Notifications • State transfer • Event-sourcing • CQRS event-driven arch. Source: https://martinfowler.com/articles/201701-event-driven.html

Why are we throwing away our events in our applications?

Accountants and banks have known this for centuries

update accounts set balance = balance + 100 where id = ‘ryans-account’ update accounts set balance = balance - 100 where id = ‘someone-elses-account’

}, { event: ‘transaction-initiated’, from: ‘someone-elses-account’, to: ‘ryans-account’, amount: 100, timestamp: ‘2017-12-13T09:30:00’ }, {

Databases also know this: transaction logs

Apache Kafka: “distributed commit log”

So what makes this a good idea?

“You can’t have your cake and eat it”

Build a better product Provide a natural audit log Fix state, not just bugs Decouple services De-risk launches benefits

Item Quantity Pixel 2 1

Event Parameters Added Item To Cart Item: iPhone X, Quantity: 1 Changed Item Quantity Item: iPhone X, Quantity: 2 Removed Item From Cart Item: iPhone X Added Item To Cart Item: Pixel 2, Quantity: 2 Changed Item Quantity Item: Pixel 2, Quantity: 1

Item Quantity Pixel 2 1 iPhone X 2

Type Parameters Added Item To Cart Item: iPhone X, Quantity: 1 Changed Item Quantity Item: iPhone X, Quantity: 2 Removed Item From Cart Item: iPhone X Added Item To Cart Item: Pixel 2, Quantity: 2 Changed Item Quantity Item: Pixel 2, Quantity: 1 Event Parameters Added Item To Cart Item: iPhone X, Quantity: 1 Changed Item Quantity Item: iPhone X, Quantity: 2 Removed Item From Cart Item: iPhone X Added Item To Cart Item: Pixel 2, Quantity: 2 Changed Item Quantity Item: Pixel 2, Quantity: 1

Item Quantity Pixel 2 1 iPhone X 2

Item Quantity Pixel 2 1 ✅

⚫ ⚫ ⚫ ⚫ ⚫ ⚫ ⚫ ⚫ ⚫

⚫ ⚫ ⚫ ⚫ ⚫ ⚫ ⚫ ⚫ ⚫

⚫ ⚫ ⚫ ⚫ ⚫ ⚫ ⚫ ⚫ ⚫

“an immutable, time-ordered sequence of events as our primary store of state” Chris Castle, @crc

Event-driven architecture isn’t a silver bullet…

downsides ⏲ Asynchronicity & eventual consistency ✏ Corrections need events Replaying must factor in external systems Doesn’t play well with CRUD Demand on storage *

Event Streaming

Votes Tweets Tweets Votes Votes Tweets Consumers Tweet Analyser Tweet Broadcaster Vote Broadcaster Vote Persister Event Stream

Votes Tweets Tweets, Votes Tweets Consumers Tweet Analyser Message Archiver Event Stream

Event-Sourcing & CQRS

Command Query Responsibility Segregation • Commonly paired with event-sourcing • The two aren’t mutually exclusive • Sounds complicated, but isn’t… • Reality: your input and output don’t share models or APIs • Great way to collect user intent cqrs

❗ ❓ alter read Command Query State cqrs

❗ ❓ generates reads Command Query State Events alter cqrs

REST vs CQRS REST • PATCH /line_items/123 • Updating quantity? • Adding a custom logo? CQRS • /update_line_item_quantity • /update_custom_graphic • Specific methods

GraphQL Mutations : CQRS

Why Apache Kafka? Open-sourced by LinkedIn, now 1.0 Fault-tolerant and robust Deliverability guarantees ⏰ Chronological ordering of messages ⬇ Pull-based asynchronous processing event stream

Why Kafka on Heroku? ⚡ Instant provisioning Plans from $100/mo High-availability as standard ↔ Easy to share between applications Thoughtful developer experience event stream

I know what event-driven architecture means I know what event sourcing means I know what CQRS means summary

Thank you Code Europe

Kafka vs RabbitMQ • Kafka is more horizontally-scalable • Kafka is better at acting as a buffer • RabbitMQ has per-message acknowledgements • Kafka has message offset acknowledgement • Both have ordering guarantees • Kafka can handle higher message input