Spring Boot + K8S : Event-Driven Microservices

 

The purpose of this blog post is to explain, how we can achieve event-driven microservices with spring boot and kubernetes.

The original source of this blog post is below youtube channel.

 

• Please find the source code for this post in here:

https://github.com/dhanuka84/kbe-sb-microservices/tree/fixes

What is the difference

 https://github.com/dhanuka84/kbe-sb-microservices/pull/1/commits

1. Fixed unit test failure due to SQL script not compatible with H2 DB

2. Images can be build locally and use same docker images with minikube.

3. MySQL datasource username configuration fix.

4. Simple and Short explanation.

How to build and test

1. Build  java project & run unit tests

mvn clean package

2.  Start minikube

start minikube

# this is important otherwise k8s cluster can't pull the docker image

eval $(minikube docker-env)

3. Build docker images

mvn spring-boot:build-image

Deploy containers in kubernetes

minikube tunnel

kubectl apply -f ./kbe-sb-microservices/k8s-scripts

Explaining the flow and components

1. Gateway : this will route API path to the correct URI

2. Order-Service  Micro-Service: placing an order

• Let's take order service micro-service and it's placeOrder() method/API.

• Controller will call the BeerOrder service and then it's business logic

• Then BeerOrderManager will call state machine to start the spring boot event bus flow.

• According to state machine configuration, next  event is BeerOrderEventEnum.VALIDATE_ORDER and next action is validateBeerOrder .

• Now this will trigger the validateBeerOrder action and it will send ValidateBeerOrderRequest to VALIDATE_ORDER_QUEUE JMS queue.

• Now our second micro-service called Beer-Service will listen to this VALIDATE_ORDER_QUEUE, and validate the beer order and send the result to another JMS queue called VALIDATE_ORDER_RESULT_QUEUE

Then again, Order-Service micro-service will listen to validation result queue and process the order and update the status of the order.

Monitoring

• Filebeat will collect all the docker logs and ingest them into Elastisearch.
• So then we can monitor application logs using Kibana.

Key takeaways

• Microservices communicated with each other in an event-driven manner using JMS queue.
• Spring Boot state machine (event bus) has been used to simplifying the business flow of the application. 
• Using above two techniques, events and states has been managed both in standalone and distributed way.
• Centralized logging can be used to trouble shoot and monitor distributed applications.

Spring Boot Exception Handling & Validation

 

The purpose of the blog post is to explain how to do exception handling and data transferring.

Please find the source code for above application. You have to select branch called improved .

This is the improved version of the code explained in previous blog post.

Rest Controller

• Only Rest API related coding included.
• DTO send to service layer

Service Implementation

• Validation happen inside the business logic .
• Exception propagate to controller level.
• DTO used to communicate with web layer.

Controller Advice

• This will capture each exception and send relevant response to client through controller.

Testing

I have used postman to test Rest API.

• You can see that HTTP response code is 204 : No Content
• We are sending timestamp, which is older than 60 seconds time period
• Inside the service layer, we have validated this and throw TimeExceeded  Exception.
• According to our controller advice, we should send HTTP response code 204 : No Content