About CQRS - Command Query Responsibility Segregation

According with Martin Folwer

At its heart is the notion that you can use a different model to update information than the model you use to read information. For some situations, this separation can be valuable, but beware that for most systems CQRS adds risky complexity.

The application

Simulates a bank account scenario where an end user adds a income or expense transaction, and it is processed in a ascyncronous event sourcing and CQRS architecture to recalculate the user's bank account balance. The user can also request the balance of it's account. Down here you can see the design:

Deploying the external services

docker-compose up -d --build

It will deploy four docker containers on your environment with MongoDB, PostgreSQL, Kafka and Zookepper (required by Kafka)

After deploying Kafka, you'll need to create the topic on the Kafka cluster. For example:

docker exec -it bankaccount-kafka \
  ./bin/kafka-topics.sh --create \
  --topic transactions \
  --zookeeper bankaccount-zookeeper:2181 \
  --replication-factor 1 \
  --partitions 1

Testing the application

Running a CURL request to create a income transaction

curl -X POST -H "Content-Type: application/json" -d @income-transaction.json http://localhost:8080/transactions

Running a CURL request to create a expense transaction

curl -X POST -H "Content-Type: application/json" -d @expense-transaction.json http://localhost:8080/transactions

Running CURL request to fetch the balance

curl http://localhost:8081/balance\?accountId\=wesley | json_pp

Running K6's simple performance test

k6 run --vus 10 --duration 60s performance-tests/income.js
k6 run --vus 10 --duration 60s performance-tests/expense.js

Contributing

I'd love to have a frontend for it! Please reach me out if you got interested