Inter-service Communication

Communication Strategies

Arya Banking utilizes three primary communication patterns to ensure scalability, security, and loose coupling.

1. Synchronous Feign (REST)

Internal service-to-service calls are handled by OpenFeign. To secure these calls, we use the OAuth2 Client Credentials grant.

Machine-to-Machine (M2M) Flow

1. Source Service (e.g., Auth Service) triggers a Feign call.
2. OAuth2 Interceptor requests a machine-to-machine JWT from Keycloak using its own client-id and client-secret.
3. Keycloak returns a JWT with ROLE_INTERNAL_SERVICE.
4. Source Service injects Authorization: Bearer <JWT> into the outgoing request.
5. Target Service (e.g., User Service) validates the JWT and verifies the role.

Implementation Pattern

// OAuth2FeignConfig (Common Library pattern)
@Bean
public RequestInterceptor oauth2RequestInterceptor() {
    return requestTemplate -> {
        OAuth2AuthorizeRequest request = OAuth2AuthorizeRequest
            .withClientRegistrationId(clientRegistrationId).build();
        OAuth2AuthorizedClient client = authorizedClientManager.authorize(request);
        requestTemplate.header("Authorization", "Bearer " + client.getAccessToken().getTokenValue());
    };
}

2. API Flow Deep-Dive

User Registration Sync

When a user registers, the flow spans two services:

Account Locking (Login Failures)

When login fails multiple times, the Auth Service signals the User Service:

3. Asynchronous Events (Kafka)

State changes are propagated asynchronously using Apache Kafka and Avro Schemas.

Primary Topic: user.create.event

Published by: user-service.

Producer Logic (UserCreateProducer)

The UserCreateProducer in the User Service uses a typed KafkaTemplate to send Avro-encoded records. These records ensure schema compatibility across the platform.

// Example usage in UserServiceImpl
userCreateProducer.sendUserCreateEvent(
    UserCreateEvent.newBuilder()
        .setUserId(user.getUserId())
        .setStatus(RegistrationConstants.BASIC_DETAILS_ADDED.getSubStatus())
        .build()
);

4. Port & Path Mapping Reference