Async-Communication Using Kafka

• Order → Inventory (sync comm) to check whether inventory is available , while placing the order.
• 
• Order service will make a request to Notification Service and will not wait for the response.
• This type of communication is called Async communication.
• Async communication can be enabled using Event driven architecture.
• i.e performing async communication in the form of events.
• So whenever we receive an order to order microservice and the order is placed successfully.
• The order microservice will raise an event like “OrderPlacedEvent” , we can add this event to a queue in Kafka or any messaging system.
• The consumer, here the Notification Service will consume the message and process the message accordingly.

docker compose up -d docker ps docker logs -f broker

Configure kafka in order service

Spring for Apache Kafka. (in chrome)

KafkaTemplate (producer)

@KafkaTemplate

       <dependency>
        <groupId>org.springframework.kafka</groupId>
        <artifactId>spring-kafka</artifactId>
       </dependency>

• in producer microservice

      spring:
        kafka:
          bootstrapServers: localhost:9092
          producer:
            keySerializer: org.apache.kafka.common.serialization.StringSerializer
            valueSerializer: org.springframework.kafka.support.serializer.JsonSerializer
            properties:
              spring:
                json:
                  type:
                    mapping: event:com.example.orderservice.event.OrderPlacedEvent
          template:
            defaultTopic: notificationTopic
  

• In the service layer

     @Autowired
     KafkaTemplate<String,OrderPlacedEvent> kafkaTemplate;
  
          kafkaTemplate.send("notificationTopic", new OrderPlacedEvent(order.getOrderNumber()));
  

• in consumer microservice

        kafka:
          bootstrapServers: localhost:9092
          consumer:
            groupId: notificationId
            keyDeserializer: org.apache.kafka.common.serialization.StringDeserializer
            valueDeserializer: org.springframework.kafka.support.serializer.JsonDeserializer
            properties:
              spring:
                json:
                  type:
                    mapping: event:com.example.notificationservice.OrderPlacedEvent
          template:
            defaultTopic: notificationTopic
  

• In service layer

     @KafkaListener(topics = "notificationTopic")
     public void handleNotification(OrderPlacedEvent orderPlacedEvent){
     log.info("Notification received- {}",orderPlacedEvent.getOrderNumber());
     }