Event Sourcing In Node.js Tamar Twena-Stern 

Tamar Twena-Stern • Software Engineer - manager and architect • Architect @PaloAltoNetworks • Was a CTO of my own startup • Passionate about Node.js ! • Twitter: @SternTwena 

Tamar Tena-Stern • On Maternity Leave • Have 3 kids • Loves to play my violin 

Let’s Write Twitter ! 

Building Newsfeed 

And We Get 

How Will That Work ? 

Why Does This Happen? 

Can I Add One More Index? username firstName lastName @johnsmith John Smith @tamarstern Tamar Stern @urishaked Uri Shaked Eventually, it breaks … 

Lets Introduce You To Our Frustrated System Administrator 

Event Sourcing 

Event Sourcing 

Demo - Node.js Event Sourcing Server 

Advantages • Each View has its own storage which is the most optimised for its specific queries • Can scale up to 10^8 of concurrent users • Schema migration is much simpler, Schema is much more flexible • System recovery is easier 

Event Log 

Where To Store Events ? • Event Store Database • Hadoop Cluster • node-webhdfs • Couchbase eventing service • npm couchbase • Implement in serverless architecture 

NPM Libraries • eventstore - Node.js event log pattern implementation • nest-cqrs 

Batch Consumer 

Evolution Of Architecture (So Far) The State Of The Entities In DB Actions in immutable log Consumers prepare results in batch 

What Is Happening In The Real World ? 

Stream Processing 

Stream Processing • Apache Kafka • Kafka-node • Amazon Kinesis 

Implementing Transactions With Event Sourcing • Databases have event log to implement transactions • I built a transaction engine for banking system in node.js using event sourcing • Each transaction was saved in an event log • Validation was done versus the event log to make sure the banking activity can be performed. 

• Twitter: @SternTwena