Event Driven Microservices

Event-driven microservices provide a way to access both historical and new data in the form of an append-only immutable log of events. It's also an excellent solution when we need to provide multiple departments and teams with access to the same set of data in a consistent way.

The architecture has two key components: event producers and event consumers. A producer publishes and pushes the events to consumers. Producer services and consumer services are decoupled, which allows them to be scaled, updated, and deployed independently.

Architecture

Our microservices-based system consists of the following modules:

• config-service - a service that uses Spring Cloud Config Server for running configuration server. The configuration files are placed on the classpath. Database and email information are securely stored on the Vault server.
• gateway-service - a flexible way of routing requests based on a number of criteria, as well as focuses on cross-cutting concerns such as security, resiliency, and monitoring.
• discovery-service - discovery client retrieves a list of all connected peers in a service registry, and makes all further requests to other services through a load-balancing algorithm.
• order-service - a service responsible for creating orders. It communicates with both stock-service and email-service.
• stock-service - when an order is created, it listens to kafka topic and performs the necessary stock transactions. It communicates with order-service.
• email-service - when an order is created, it listens to kafka topic and sends the created order information to the customer as an email. It communicates with order-service.
• kafka-config - a module containing the Producer and Consumer configurations.

Creating secrets in Vault

Initializing Server (you will get unseal and token keys)

$ vault operator init

Unseal the server (enter your unseal keys for 3 times)

$ vault operator unseal

Login with token

$ vault login

Enabling Key-Value Secret engine with version 2

$ vault secrets enable -version=2 kv

Creating Vault secrets

$ vault kv put kv/<your-secret> EMAIL_USERNAME=<your-email> EMAIL_PASSWORD=<your-app-pass> DB_USERNAME=<db-user> DB_PASSWORD=<db-pass>

Finally, modify application.yml with your secret (default-key) in the config-service, then add an environment variable to your system with the VAULT_TOKEN key and give your token as a value.

Usage

Build the apps with images:

$ mvn clean package -Pbuild-image

Then run all the containers with docker-compose:

$ docker-compose up

TODO

• Kafka Streams
• Kubernetes
• JUnit Testing with Mockito
• Spring Doc
• Redis