Cortex Architecture for Scalability in Java: Complete Implementation Guide

Cortex is a scalable, event-driven architecture pattern inspired by brain-like processing. This guide covers implementing Cortex architecture in Java for building highly scalable, resilient distributed systems.

Cortex Architecture Overview

Core Principles:

Event-Driven: Asynchronous message processing
Microservices: Decoupled, specialized services
CQRS: Command Query Responsibility Segregation
Event Sourcing: State changes as event sequences
Resilience: Circuit breakers, retries, fallbacks

Key Components:

Cortex Core: Event bus and message routing
Neurons: Specialized processing units
Synapses: Inter-neuron communication channels
Axons: Long-distance communication
Dendrites: Input receivers

Dependencies and Setup

Maven Dependencies

<properties> <spring-boot.version>3.1.0</spring-boot.version> <axon.version>4.8.0</axon.version> <resilience4j.version>2.1.0</resilience4j.version> <kafka.version>3.4.0</kafka.version> </properties> <dependencies> <!-- Spring Boot --> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> <version>${spring-boot.version}</version> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-data-jpa</artifactId> <version>${spring-boot.version}</version> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-actuator</artifactId> <version>${spring-boot.version}</version> </dependency> <!-- Axon Framework (Event Sourcing & CQRS) --> <dependency> <groupId>org.axonframework</groupId> <artifactId>axon-spring-boot-starter</artifactId> <version>${axon.version}</version> </dependency> <!-- Resilience4j --> <dependency> <groupId>io.github.resilience4j</groupId> <artifactId>resilience4j-spring-boot3</artifactId> <version>${resilience4j.version}</version> </dependency> <dependency> <groupId>io.github.resilience4j</groupId> <artifactId>resilience4j-circuitbreaker</artifactId> <version>${resilience4j.version}</version> </dependency> <dependency> <groupId>io.github.resilience4j</groupId> <artifactId>resilience4j-retry</artifactId> <version>${resilience4j.version}</version> </dependency> <!-- Messaging --> <dependency> <groupId>org.springframework.kafka</groupId> <artifactId>spring-kafka</artifactId> <version>${kafka.version}</version> </dependency> <!-- Database --> <dependency> <groupId>org.postgresql</groupId> <artifactId>postgresql</artifactId> <scope>runtime</scope> </dependency> <dependency> <groupId>com.h2database</groupId> <artifactId>h2</artifactId> <scope>test</scope> </dependency> <!-- Caching --> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-data-redis</artifactId> <version>${spring-boot.version}</version> </dependency> <!-- Monitoring --> <dependency> <groupId>io.micrometer</groupId> <artifactId>micrometer-registry-prometheus</artifactId> </dependency> <!-- Testing --> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-test</artifactId> <version>${spring-boot.version}</version> <scope>test</scope> </dependency> <dependency> <groupId>org.axonframework</groupId> <artifactId>axon-test</artifactId> <version>${axon.version}</version> <scope>test</scope> </dependency> </dependencies>

Application Configuration

# application.yml server: port: 8080 spring: application: name: cortex-system datasource: url: jdbc:postgresql://localhost:5432/cortex username: postgres password: password driver-class-name: org.postgresql.Driver jpa: hibernate: ddl-auto: update properties: hibernate: dialect: org.hibernate.dialect.PostgreSQLDialect format_sql: true show-sql: false kafka: bootstrap-servers: localhost:9092 consumer: group-id: cortex-group auto-offset-reset: earliest producer: acks: all retries: 3 data: redis: host: localhost port: 6379 axon: axonserver: servers: localhost:8124 eventhandling: processors: cortex-processor: mode: tracking source: kafkaMessageSource resilience4j: circuitbreaker: instances: cortex-service: register-health-indicator: true sliding-window-size: 10 minimum-number-of-calls: 5 permitted-number-of-calls-in-half-open-state: 3 automatic-transition-from-open-to-half-open-enabled: true wait-duration-in-open-state: 10s failure-rate-threshold: 50 event-consumer-buffer-size: 10 retry: instances: cortex-service: max-attempts: 3 wait-duration: 2s management: endpoints: web: exposure: include: health,metrics,info,prometheus endpoint: health: show-details: always

Core Cortex Architecture

1. Event Base Classes

public abstract class CortexEvent { protected final String eventId; protected final String correlationId; protected final String neuronId; protected final LocalDateTime timestamp; protected final Map<String, Object> metadata; protected CortexEvent(String correlationId, String neuronId) { this.eventId = UUID.randomUUID().toString(); this.correlationId = correlationId; this.neuronId = neuronId; this.timestamp = LocalDateTime.now(); this.metadata = new HashMap<>(); } // Getters public String getEventId() { return eventId; } public String getCorrelationId() { return correlationId; } public String getNeuronId() { return neuronId; } public LocalDateTime getTimestamp() { return timestamp; } public Map<String, Object> getMetadata() { return Collections.unmodifiableMap(metadata); } public void addMetadata(String key, Object value) { metadata.put(key, value); } public abstract String getEventType(); } public abstract class DomainEvent extends CortexEvent { protected final String aggregateId; protected DomainEvent(String aggregateId, String correlationId, String neuronId) { super(correlationId, neuronId); this.aggregateId = aggregateId; } public String getAggregateId() { return aggregateId; } } public abstract class IntegrationEvent extends CortexEvent { protected final String sourceService; protected final String destinationService; protected IntegrationEvent(String sourceService, String destinationService, String correlationId, String neuronId) { super(correlationId, neuronId); this.sourceService = sourceService; this.destinationService = destinationService; } // Getters public String getSourceService() { return sourceService; } public String getDestinationService() { return destinationService; } }

2. Command Base Classes

public abstract class CortexCommand { protected final String commandId; protected final String correlationId; protected final String neuronId; protected final LocalDateTime timestamp; protected CortexCommand(String correlationId, String neuronId) { this.commandId = UUID.randomUUID().toString(); this.correlationId = correlationId; this.neuronId = neuronId; this.timestamp = LocalDateTime.now(); } // Getters public String getCommandId() { return commandId; } public String getCorrelationId() { return correlationId; } public String getNeuronId() { return neuronId; } public LocalDateTime getTimestamp() { return timestamp; } public abstract String getCommandType(); } public abstract class DomainCommand extends CortexCommand { protected final String aggregateId; protected DomainCommand(String aggregateId, String correlationId, String neuronId) { super(correlationId, neuronId); this.aggregateId = aggregateId; } public String getAggregateId() { return aggregateId; } }

3. Query Base Classes

public abstract class CortexQuery { protected final String queryId; protected final String correlationId; protected final String neuronId; protected final LocalDateTime timestamp; protected CortexQuery(String correlationId, String neuronId) { this.queryId = UUID.randomUUID().toString(); this.correlationId = correlationId; this.neuronId = neuronId; this.timestamp = LocalDateTime.now(); } // Getters public String getQueryId() { return queryId; } public String getCorrelationId() { return correlationId; } public String getNeuronId() { return neuronId; } public LocalDateTime getTimestamp() { return timestamp; } public abstract String getQueryType(); public abstract Class<?> getResponseType(); } public class QueryResult<T> { private final String queryId; private final String correlationId; private final T data; private final boolean success; private final String errorMessage; private QueryResult(String queryId, String correlationId, T data, boolean success, String errorMessage) { this.queryId = queryId; this.correlationId = correlationId; this.data = data; this.success = success; this.errorMessage = errorMessage; } public static <T> QueryResult<T> success(String queryId, String correlationId, T data) { return new QueryResult<>(queryId, correlationId, data, true, null); } public static <T> QueryResult<T> failure(String queryId, String correlationId, String error) { return new QueryResult<>(queryId, correlationId, null, false, error); } // Getters public String getQueryId() { return queryId; } public String getCorrelationId() { return correlationId; } public T getData() { return data; } public boolean isSuccess() { return success; } public String getErrorMessage() { return errorMessage; } }

Cortex Core Infrastructure

1. Event Bus Implementation

@Component @Slf4j public class CortexEventBus { private final ApplicationEventPublisher applicationEventPublisher; private final Map<String, List<EventHandler>> eventHandlers = new ConcurrentHashMap<>(); private final EventProcessorRegistry eventProcessorRegistry; public CortexEventBus(ApplicationEventPublisher applicationEventPublisher, EventProcessorRegistry eventProcessorRegistry) { this.applicationEventPublisher = applicationEventPublisher; this.eventProcessorRegistry = eventProcessorRegistry; } public void publish(CortexEvent event) { log.debug("Publishing event: {} [ID: {}]", event.getEventType(), event.getEventId()); // Publish to local Spring application context applicationEventPublisher.publishEvent(event); // Notify registered handlers notifyHandlers(event); // Process through Axon framework if it's a domain event if (event instanceof DomainEvent) { processDomainEvent((DomainEvent) event); } } public void subscribe(String eventType, EventHandler handler) { eventHandlers.computeIfAbsent(eventType, k -> new CopyOnWriteArrayList<>()) .add(handler); log.debug("Subscribed handler for event type: {}", eventType); } public void unsubscribe(String eventType, EventHandler handler) { List<EventHandler> handlers = eventHandlers.get(eventType); if (handlers != null) { handlers.remove(handler); log.debug("Unsubscribed handler for event type: {}", eventType); } } private void notifyHandlers(CortexEvent event) { String eventType = event.getEventType(); List<EventHandler> handlers = eventHandlers.get(eventType); if (handlers != null) { handlers.forEach(handler -> { try { handler.handle(event); } catch (Exception e) { log.error("Error handling event {} by handler {}", eventType, handler.getClass().getSimpleName(), e); } }); } } private void processDomainEvent(DomainEvent event) { // This would integrate with Axon EventBus in a real implementation log.debug("Processing domain event through Axon: {}", event.getEventType()); } @FunctionalInterface public interface EventHandler { void handle(CortexEvent event); } }

2. Neuron Base Class

public abstract class Neuron { protected final String neuronId; protected final String neuronType; protected final CortexEventBus eventBus; protected final NeuronHealth health; protected final Map<String, Object> state; protected Neuron(String neuronId, String neuronType, CortexEventBus eventBus) { this.neuronId = neuronId; this.neuronType = neuronType; this.eventBus = eventBus; this.health = new NeuronHealth(neuronId); this.state = new ConcurrentHashMap<>(); initialize(); } protected abstract void initialize(); protected abstract void processEvent(CortexEvent event); protected abstract void processCommand(CortexCommand command); protected void publishEvent(CortexEvent event) { eventBus.publish(event); health.recordEventPublished(); } protected void updateHealth(HealthStatus status, String message) { health.updateStatus(status, message); } protected void updateState(String key, Object value) { state.put(key, value); } protected <T> T getState(String key, Class<T> type) { return type.cast(state.get(key)); } // Getters public String getNeuronId() { return neuronId; } public String getNeuronType() { return neuronType; } public NeuronHealth getHealth() { return health; } public Map<String, Object> getState() { return Collections.unmodifiableMap(state); } public void handleEvent(CortexEvent event) { try { health.recordEventProcessed(); processEvent(event); health.recordSuccess(); } catch (Exception e) { health.recordError(e.getMessage()); log.error("Error processing event in neuron {}: {}", neuronId, e.getMessage(), e); handleError(event, e); } } public void handleCommand(CortexCommand command) { try { health.recordCommandProcessed(); processCommand(command); health.recordSuccess(); } catch (Exception e) { health.recordError(e.getMessage()); log.error("Error processing command in neuron {}: {}", neuronId, e.getMessage(), e); handleError(command, e); } } protected void handleError(Object message, Exception error) { // Default error handling - can be overridden by specific neurons ErrorEvent errorEvent = new ErrorEvent( neuronId, message.getClass().getSimpleName(), error.getMessage(), health.getCorrelationId() ); publishEvent(errorEvent); } } public class NeuronHealth { private final String neuronId; private HealthStatus status; private String message; private long eventsProcessed; private long commandsProcessed; private long eventsPublished; private long errors; private long successes; private LocalDateTime lastActivity; private final String correlationId; public NeuronHealth(String neuronId) { this.neuronId = neuronId; this.status = HealthStatus.HEALTHY; this.message = "Neuron initialized"; this.correlationId = UUID.randomUUID().toString(); this.lastActivity = LocalDateTime.now(); } public void updateStatus(HealthStatus status, String message) { this.status = status; this.message = message; this.lastActivity = LocalDateTime.now(); } public void recordEventProcessed() { eventsProcessed++; lastActivity = LocalDateTime.now(); } public void recordCommandProcessed() { commandsProcessed++; lastActivity = LocalDateTime.now(); } public void recordEventPublished() { eventsPublished++; lastActivity = LocalDateTime.now(); } public void recordError(String errorMessage) { errors++; updateStatus(HealthStatus.UNHEALTHY, errorMessage); } public void recordSuccess() { successes++; if (status == HealthStatus.UNHEALTHY) { updateStatus(HealthStatus.HEALTHY, "Recovered from previous errors"); } } // Getters public String getNeuronId() { return neuronId; } public HealthStatus getStatus() { return status; } public String getMessage() { return message; } public long getEventsProcessed() { return eventsProcessed; } public long getCommandsProcessed() { return commandsProcessed; } public long getEventsPublished() { return eventsPublished; } public long getErrors() { return errors; } public long getSuccesses() { return successes; } public LocalDateTime getLastActivity() { return lastActivity; } public String getCorrelationId() { return correlationId; } public double getErrorRate() { long totalOperations = eventsProcessed + commandsProcessed; return totalOperations > 0 ? (double) errors / totalOperations : 0.0; } public boolean isHealthy() { return status == HealthStatus.HEALTHY; } } public enum HealthStatus { HEALTHY, DEGRADED, UNHEALTHY, OFFLINE }

3. Synapse Communication

@Component @Slf4j public class SynapseRouter { private final Map<String, List<Neuron>> routingTable = new ConcurrentHashMap<>(); private final CortexEventBus eventBus; private final CircuitBreakerRegistry circuitBreakerRegistry; private final RetryRegistry retryRegistry; public SynapseRouter(CortexEventBus eventBus, CircuitBreakerRegistry circuitBreakerRegistry, RetryRegistry retryRegistry) { this.eventBus = eventBus; this.circuitBreakerRegistry = circuitBreakerRegistry; this.retryRegistry = retryRegistry; setupEventForwarding(); } public void registerNeuron(String eventType, Neuron neuron) { routingTable.computeIfAbsent(eventType, k -> new CopyOnWriteArrayList<>()) .add(neuron); log.info("Registered neuron {} for event type: {}", neuron.getNeuronId(), eventType); } public void unregisterNeuron(String eventType, Neuron neuron) { List<Neuron> neurons = routingTable.get(eventType); if (neurons != null) { neurons.remove(neuron); log.info("Unregistered neuron {} from event type: {}", neuron.getNeuronId(), eventType); } } public void routeEvent(CortexEvent event) { String eventType = event.getEventType(); List<Neuron> targetNeurons = routingTable.get(eventType); if (targetNeurons == null || targetNeurons.isEmpty()) { log.warn("No neurons registered for event type: {}", eventType); return; } targetNeurons.forEach(neuron -> forwardEventToNeuron(event, neuron)); } public void routeCommand(CortexCommand command, String targetNeuronId) { // Direct command routing to specific neuron // Implementation would find neuron by ID and forward command log.debug("Routing command to neuron: {}", targetNeuronId); } private void forwardEventToNeuron(CortexEvent event, Neuron neuron) { CircuitBreaker circuitBreaker = circuitBreakerRegistry.circuitBreaker("cortex-service"); Retry retry = retryRegistry.retry("cortex-service"); Supplier<Void> eventForwarding = () -> { if (neuron.getHealth().isHealthy()) { neuron.handleEvent(event); } else { log.warn("Skipping unhealthy neuron: {}", neuron.getNeuronId()); // Could implement fallback strategies here } return null; }; // Apply resilience patterns Supplier<Void> decoratedSupplier = CircuitBreaker.decorateSupplier(circuitBreaker, eventForwarding); decoratedSupplier = Retry.decorateSupplier(retry, decoratedSupplier); try { decoratedSupplier.get(); } catch (Exception e) { log.error("Failed to forward event to neuron {}: {}", neuron.getNeuronId(), e.getMessage()); handleRoutingFailure(event, neuron, e); } } private void handleRoutingFailure(CortexEvent event, Neuron neuron, Exception error) { RoutingFailureEvent failureEvent = new RoutingFailureEvent( event.getEventId(), neuron.getNeuronId(), error.getMessage(), event.getCorrelationId() ); eventBus.publish(failureEvent); } private void setupEventForwarding() { // Subscribe to all events and route them appropriately eventBus.subscribe(".*", this::routeEvent); } public Map<String, List<String>> getRoutingTable() { return routingTable.entrySet().stream() .collect(Collectors.toMap( Map.Entry::getKey, entry -> entry.getValue().stream() .map(Neuron::getNeuronId) .collect(Collectors.toList()) )); } }

4. Axon Integration for Event Sourcing

@Configuration @EnableAxon public class AxonConfiguration { @Bean public EventStorageEngine eventStorageEngine(DataSource dataSource) { return JpaEventStorageEngine.builder() .dataSource(dataSource) .build(); } @Bean public TokenStore tokenStore(DataSource dataSource) { return JpaTokenStore.builder() .dataSource(dataSource) .serializer(JacksonSerializer.defaultSerializer()) .build(); } @Bean public SagaStore sagaStore(DataSource dataSource) { return JpaSagaStore.builder() .dataSource(dataSource) .build(); } } @Component @Slf4j public class AxonEventProcessor { private final EventBus eventBus; private final EventStore eventStore; private final CommandBus commandBus; private final QueryBus queryBus; public AxonEventProcessor(EventBus eventBus, EventStore eventStore, CommandBus commandBus, QueryBus queryBus) { this.eventBus = eventBus; this.eventStore = eventStore; this.commandBus = commandBus; this.queryBus = queryBus; } public void processDomainEvent(DomainEvent event) { try { // Convert to Axon event and publish org.axonframework.eventhandling.GenericDomainEventMessage.asEventMessage(event); eventBus.publish(org.axonframework.eventhandling.GenericDomainEventMessage.asEventMessage(event)); log.debug("Processed domain event through Axon: {}", event.getEventType()); } catch (Exception e) { log.error("Failed to process domain event through Axon: {}", e.getMessage(), e); throw new CortexRuntimeException("Axon event processing failed", e); } } public <R> CompletableFuture<R> sendCommand(Object command) { return commandBus.send(command); } public <R> CompletableFuture<R> sendQuery(Object query) { return queryBus.query(query, ResponseTypes.instanceOf((Class<R>) query.getClass())); } }

Example: E-commerce Cortex Implementation

1. Domain Events

// Product Events public class ProductCreatedEvent extends DomainEvent { private final String productId; private final String name; private final String description; private final BigDecimal price; private final int initialStock; public ProductCreatedEvent(String productId, String name, String description, BigDecimal price, int initialStock, String correlationId) { super(productId, correlationId, "product-neuron"); this.productId = productId; this.name = name; this.description = description; this.price = price; this.initialStock = initialStock; } @Override public String getEventType() { return "PRODUCT_CREATED"; } // Getters public String getProductId() { return productId; } public String getName() { return name; } public String getDescription() { return description; } public BigDecimal getPrice() { return price; } public int getInitialStock() { return initialStock; } } public class ProductStockUpdatedEvent extends DomainEvent { private final String productId; private final int newStock; private final int oldStock; private final String reason; public ProductStockUpdatedEvent(String productId, int newStock, int oldStock, String reason, String correlationId) { super(productId, correlationId, "inventory-neuron"); this.productId = productId; this.newStock = newStock; this.oldStock = oldStock; this.reason = reason; } @Override public String getEventType() { return "PRODUCT_STOCK_UPDATED"; } // Getters public String getProductId() { return productId; } public int getNewStock() { return newStock; } public int getOldStock() { return oldStock; } public String getReason() { return reason; } } // Order Events public class OrderCreatedEvent extends DomainEvent { private final String orderId; private final String customerId; private final List<OrderItem> items; private final BigDecimal totalAmount; private final OrderStatus status; public OrderCreatedEvent(String orderId, String customerId, List<OrderItem> items, BigDecimal totalAmount, String correlationId) { super(orderId, correlationId, "order-neuron"); this.orderId = orderId; this.customerId = customerId; this.items = items; this.totalAmount = totalAmount; this.status = OrderStatus.CREATED; } @Override public String getEventType() { return "ORDER_CREATED"; } // Getters public String getOrderId() { return orderId; } public String getCustomerId() { return customerId; } public List<OrderItem> getItems() { return items; } public BigDecimal getTotalAmount() { return totalAmount; } public OrderStatus getStatus() { return status; } } public class OrderStatusUpdatedEvent extends DomainEvent { private final String orderId; private final OrderStatus oldStatus; private final OrderStatus newStatus; private final String reason; public OrderStatusUpdatedEvent(String orderId, OrderStatus oldStatus, OrderStatus newStatus, String reason, String correlationId) { super(orderId, correlationId, "order-neuron"); this.orderId = orderId; this.oldStatus = oldStatus; this.newStatus = newStatus; this.reason = reason; } @Override public String getEventType() { return "ORDER_STATUS_UPDATED"; } // Getters public String getOrderId() { return orderId; } public OrderStatus getOldStatus() { return oldStatus; } public OrderStatus getNewStatus() { return newStatus; } public String getReason() { return reason; } }

2. Neurons Implementation

@Component @Slf4j public class ProductNeuron extends Neuron { private final ProductRepository productRepository; private final AxonEventProcessor axonProcessor; public ProductNeuron(CortexEventBus eventBus, ProductRepository productRepository, AxonEventProcessor axonProcessor) { super("product-neuron", "PRODUCT_MANAGEMENT", eventBus); this.productRepository = productRepository; this.axonProcessor = axonProcessor; } @Override protected void initialize() { // Subscribe to relevant events eventBus.subscribe("PRODUCT_CREATED", this::handleEvent); eventBus.subscribe("PRODUCT_UPDATED", this::handleEvent); log.info("Product neuron initialized: {}", neuronId); updateHealth(HealthStatus.HEALTHY, "Product neuron ready"); } @Override protected void processEvent(CortexEvent event) { if (event instanceof ProductCreatedEvent) { handleProductCreated((ProductCreatedEvent) event); } else if (event instanceof ProductStockUpdatedEvent) { handleStockUpdated((ProductStockUpdatedEvent) event); } } @Override protected void processCommand(CortexCommand command) { // Handle product-related commands log.debug("Processing command in product neuron: {}", command.getCommandType()); } private void handleProductCreated(ProductCreatedEvent event) { try { // Create product in read model Product product = new Product( event.getProductId(), event.getName(), event.getDescription(), event.getPrice(), event.getInitialStock() ); productRepository.save(product); updateState("productsCreated", getState("productsCreated", Integer.class) + 1); log.info("Product created: {} - {}", event.getProductId(), event.getName()); } catch (Exception e) { log.error("Failed to handle product creation: {}", e.getMessage(), e); updateHealth(HealthStatus.DEGRADED, "Product creation handling failed"); throw new CortexRuntimeException("Product creation failed", e); } } private void handleStockUpdated(ProductStockUpdatedEvent event) { try { // Update product stock in read model Product product = productRepository.findById(event.getProductId()) .orElseThrow(() -> new EntityNotFoundException("Product not found: " + event.getProductId())); product.setStockQuantity(event.getNewStock()); productRepository.save(product); updateState("stockUpdates", getState("stockUpdates", Integer.class) + 1); log.debug("Product stock updated: {} -> {}", event.getProductId(), event.getNewStock()); } catch (Exception e) { log.error("Failed to handle stock update: {}", e.getMessage(), e); throw new CortexRuntimeException("Stock update failed", e); } } } @Component @Slf4j public class OrderNeuron extends Neuron { private final OrderRepository orderRepository; private final ProductRepository productRepository; private final SynapseRouter synapseRouter; public OrderNeuron(CortexEventBus eventBus, OrderRepository orderRepository, ProductRepository productRepository, SynapseRouter synapseRouter) { super("order-neuron", "ORDER_MANAGEMENT", eventBus); this.orderRepository = orderRepository; this.productRepository = productRepository; this.synapseRouter = synapseRouter; } @Override protected void initialize() { // Subscribe to order-related events eventBus.subscribe("ORDER_CREATED", this::handleEvent); eventBus.subscribe("ORDER_STATUS_UPDATED", this::handleEvent); log.info("Order neuron initialized: {}", neuronId); updateHealth(HealthStatus.HEALTHY, "Order neuron ready"); } @Override protected void processEvent(CortexEvent event) { if (event instanceof OrderCreatedEvent) { handleOrderCreated((OrderCreatedEvent) event); } else if (event instanceof OrderStatusUpdatedEvent) { handleOrderStatusUpdated((OrderStatusUpdatedEvent) event); } } @Override protected void processCommand(CortexCommand command) { // Handle order-related commands log.debug("Processing command in order neuron: {}", command.getCommandType()); } private void handleOrderCreated(OrderCreatedEvent event) { try { // Validate product availability for (OrderItem item : event.getItems()) { Product product = productRepository.findById(item.getProductId()) .orElseThrow(() -> new EntityNotFoundException("Product not found: " + item.getProductId())); if (product.getStockQuantity() < item.getQuantity()) { throw new InsufficientStockException( "Insufficient stock for product: " + item.getProductId()); } } // Create order in read model Order order = new Order( event.getOrderId(), event.getCustomerId(), event.getItems(), event.getTotalAmount(), event.getStatus() ); orderRepository.save(order); updateState("ordersCreated", getState("ordersCreated", Integer.class) + 1); // Publish event for inventory update OrderValidatedEvent validatedEvent = new OrderValidatedEvent( event.getOrderId(), event.getCustomerId(), event.getItems(), event.getCorrelationId() ); publishEvent(validatedEvent); log.info("Order created and validated: {}", event.getOrderId()); } catch (InsufficientStockException e) { // Handle insufficient stock OrderRejectedEvent rejectedEvent = new OrderRejectedEvent( event.getOrderId(), "INSUFFICIENT_STOCK", e.getMessage(), event.getCorrelationId() ); publishEvent(rejectedEvent); log.warn("Order rejected due to insufficient stock: {}", event.getOrderId()); } catch (Exception e) { log.error("Failed to handle order creation: {}", e.getMessage(), e); updateHealth(HealthStatus.DEGRADED, "Order creation handling failed"); throw new CortexRuntimeException("Order creation failed", e); } } private void handleOrderStatusUpdated(OrderStatusUpdatedEvent event) { try { Order order = orderRepository.findById(event.getOrderId()) .orElseThrow(() -> new EntityNotFoundException("Order not found: " + event.getOrderId())); order.setStatus(event.getNewStatus()); orderRepository.save(order); updateState("statusUpdates", getState("statusUpdates", Integer.class) + 1); log.debug("Order status updated: {} -> {}", event.getOrderId(), event.getNewStatus()); } catch (Exception e) { log.error("Failed to handle order status update: {}", e.getMessage(), e); throw new CortexRuntimeException("Order status update failed", e); } } } @Component @Slf4j public class InventoryNeuron extends Neuron { private final ProductRepository productRepository; public InventoryNeuron(CortexEventBus eventBus, ProductRepository productRepository) { super("inventory-neuron", "INVENTORY_MANAGEMENT", eventBus); this.productRepository = productRepository; } @Override protected void initialize() { // Subscribe to inventory-related events eventBus.subscribe("ORDER_VALIDATED", this::handleEvent); eventBus.subscribe("PRODUCT_STOCK_UPDATED", this::handleEvent); log.info("Inventory neuron initialized: {}", neuronId); updateHealth(HealthStatus.HEALTHY, "Inventory neuron ready"); } @Override protected void processEvent(CortexEvent event) { if (event instanceof OrderValidatedEvent) { handleOrderValidated((OrderValidatedEvent) event); } } @Override protected void processCommand(CortexCommand command) { // Handle inventory-related commands log.debug("Processing command in inventory neuron: {}", command.getCommandType()); } private void handleOrderValidated(OrderValidatedEvent event) { try { // Update inventory for each product in the order for (OrderItem item : event.getItems()) { Product product = productRepository.findById(item.getProductId()) .orElseThrow(() -> new EntityNotFoundException("Product not found: " + item.getProductId())); int oldStock = product.getStockQuantity(); int newStock = oldStock - item.getQuantity(); if (newStock < 0) { throw new IllegalStateException("Stock would go negative for product: " + item.getProductId()); } product.setStockQuantity(newStock); productRepository.save(product); // Publish stock update event ProductStockUpdatedEvent stockEvent = new ProductStockUpdatedEvent( item.getProductId(), newStock, oldStock, "ORDER_FULFILLMENT", event.getCorrelationId() ); publishEvent(stockEvent); } // Publish order fulfilled event OrderFulfilledEvent fulfilledEvent = new OrderFulfilledEvent( event.getOrderId(), event.getCorrelationId() ); publishEvent(fulfilledEvent); updateState("inventoryUpdates", getState("inventoryUpdates", Integer.class) + 1); log.info("Inventory updated for order: {}", event.getOrderId()); } catch (Exception e) { log.error("Failed to handle order validation: {}", e.getMessage(), e); updateHealth(HealthStatus.DEGRADED, "Inventory update failed"); throw new CortexRuntimeException("Inventory update failed", e); } } }

3. Repository Interfaces

@Repository public interface ProductRepository extends JpaRepository<Product, String> { @Query("SELECT p FROM Product p WHERE p.stockQuantity < :threshold") List<Product> findLowStockProducts(@Param("threshold") int threshold); @Modifying @Query("UPDATE Product p SET p.stockQuantity = p.stockQuantity - :quantity WHERE p.id = :productId AND p.stockQuantity >= :quantity") int decrementStock(@Param("productId") String productId, @Param("quantity") int quantity); } @Repository public interface OrderRepository extends JpaRepository<Order, String> { List<Order> findByCustomerId(String customerId); List<Order> findByStatus(OrderStatus status); @Query("SELECT o FROM Order o WHERE o.createdAt BETWEEN :startDate AND :endDate") List<Order> findOrdersInPeriod(@Param("startDate") LocalDateTime startDate, @Param("endDate") LocalDateTime endDate); }

Cortex Management API

1. REST Controllers

@RestController @RequestMapping("/api/cortex") @Slf4j public class CortexManagementController { private final CortexEventBus eventBus; private final SynapseRouter synapseRouter; private final List<Neuron> neurons; private final AxonEventProcessor axonProcessor; public CortexManagementController(CortexEventBus eventBus, SynapseRouter synapseRouter, List<Neuron> neurons, AxonEventProcessor axonProcessor) { this.eventBus = eventBus; this.synapseRouter = synapseRouter; this.neurons = neurons; this.axonProcessor = axonProcessor; } @GetMapping("/health") public ResponseEntity<Map<String, Object>> getSystemHealth() { Map<String, Object> health = new HashMap<>(); // Neuron health Map<String, Object> neuronHealth = neurons.stream() .collect(Collectors.toMap( Neuron::getNeuronId, neuron -> Map.of( "status", neuron.getHealth().getStatus(), "message", neuron.getHealth().getMessage(), "errorRate", neuron.getHealth().getErrorRate(), "lastActivity", neuron.getHealth().getLastActivity() ) )); health.put("neurons", neuronHealth); health.put("systemStatus", calculateSystemStatus(neuronHealth)); health.put("timestamp", LocalDateTime.now()); return ResponseEntity.ok(health); } @GetMapping("/routing") public ResponseEntity<Map<String, List<String>>> getRoutingTable() { return ResponseEntity.ok(synapseRouter.getRoutingTable()); } @PostMapping("/events/publish") public ResponseEntity<Map<String, Object>> publishEvent(@RequestBody Map<String, Object> eventData) { try { String eventType = (String) eventData.get("type"); String correlationId = UUID.randomUUID().toString(); CortexEvent event = createEventFromData(eventType, eventData, correlationId); eventBus.publish(event); return ResponseEntity.ok(Map.of( "status", "success", "eventId", event.getEventId(), "correlationId", correlationId )); } catch (Exception e) { return ResponseEntity.status(HttpStatus.BAD_REQUEST) .body(Map.of( "status", "error", "message", e.getMessage() )); } } @GetMapping("/neurons/{neuronId}/state") public ResponseEntity<Map<String, Object>> getNeuronState(@PathVariable String neuronId) { Optional<Neuron> neuron = neurons.stream() .filter(n -> n.getNeuronId().equals(neuronId)) .findFirst(); if (neuron.isEmpty()) { return ResponseEntity.notFound().build(); } Map<String, Object> state = new HashMap<>(); state.put("neuronId", neuronId); state.put("state", neuron.get().getState()); state.put("health", Map.of( "status", neuron.get().getHealth().getStatus(), "eventsProcessed", neuron.get().getHealth().getEventsProcessed(), "errorRate", neuron.get().getHealth().getErrorRate() )); return ResponseEntity.ok(state); } @PostMapping("/neurons/{neuronId}/reset") public ResponseEntity<Map<String, Object>> resetNeuron(@PathVariable String neuronId) { Optional<Neuron> neuron = neurons.stream() .filter(n -> n.getNeuronId().equals(neuronId)) .findFirst(); if (neuron.isEmpty()) { return ResponseEntity.notFound().build(); } // In a real implementation, this would reset the neuron's state neuron.get().getHealth().updateStatus(HealthStatus.HEALTHY, "Manually reset"); return ResponseEntity.ok(Map.of( "status", "success", "message", "Neuron reset successfully" )); } private CortexEvent createEventFromData(String eventType, Map<String, Object> data, String correlationId) { // This would create appropriate event based on type // Simplified implementation return new CortexEvent(correlationId, "api-neuron") { @Override public String getEventType() { return eventType; } }; } private String calculateSystemStatus(Map<String, Object> neuronHealth) { long unhealthyNeurons = neuronHealth.values().stream() .filter(health -> health instanceof Map) .map(health -> (Map<?, ?>) health) .filter(health -> health.get("status") != HealthStatus.HEALTHY) .count(); if (unhealthyNeurons == 0) { return "HEALTHY"; } else if (unhealthyNeurons < neuronHealth.size() / 2) { return "DEGRADED"; } else { return "UNHEALTHY"; } } } @RestController @RequestMapping("/api/products") @Slf4j public class ProductController { private final ProductRepository productRepository; private final CortexEventBus eventBus; public ProductController(ProductRepository productRepository, CortexEventBus eventBus) { this.productRepository = productRepository; this.eventBus = eventBus; } @PostMapping public ResponseEntity<Map<String, Object>> createProduct(@RequestBody CreateProductRequest request) { try { String productId = UUID.randomUUID().toString(); String correlationId = UUID.randomUUID().toString(); ProductCreatedEvent event = new ProductCreatedEvent( productId, request.getName(), request.getDescription(), request.getPrice(), request.getInitialStock(), correlationId ); eventBus.publish(event); return ResponseEntity.accepted().body(Map.of( "status", "accepted", "productId", productId, "correlationId", correlationId )); } catch (Exception e) { return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR) .body(Map.of( "status", "error", "message", e.getMessage() )); } } @GetMapping("/{productId}") public ResponseEntity<Product> getProduct(@PathVariable String productId) { return productRepository.findById(productId) .map(ResponseEntity::ok) .orElse(ResponseEntity.notFound().build()); } @GetMapping public ResponseEntity<List<Product>> getProducts() { return ResponseEntity.ok(productRepository.findAll()); } } @RestController @RequestMapping("/api/orders") @Slf4j public class OrderController { private final OrderRepository orderRepository; private final CortexEventBus eventBus; public OrderController(OrderRepository orderRepository, CortexEventBus eventBus) { this.orderRepository = orderRepository; this.eventBus = eventBus; } @PostMapping public ResponseEntity<Map<String, Object>> createOrder(@RequestBody CreateOrderRequest request) { try { String orderId = UUID.randomUUID().toString(); String correlationId = UUID.randomUUID().toString(); // Calculate total amount BigDecimal totalAmount = request.getItems().stream() .map(item -> item.getPrice().multiply(BigDecimal.valueOf(item.getQuantity()))) .reduce(BigDecimal.ZERO, BigDecimal::add); OrderCreatedEvent event = new OrderCreatedEvent( orderId, request.getCustomerId(), request.getItems(), totalAmount, correlationId ); eventBus.publish(event); return ResponseEntity.accepted().body(Map.of( "status", "accepted", "orderId", orderId, "correlationId", correlationId, "totalAmount", totalAmount )); } catch (Exception e) { return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR) .body(Map.of( "status", "error", "message", e.getMessage() )); } } @GetMapping("/{orderId}") public ResponseEntity<Order> getOrder(@PathVariable String orderId) { return orderRepository.findById(orderId) .map(ResponseEntity::ok) .orElse(ResponseEntity.notFound().build()); } @GetMapping("/customer/{customerId}") public ResponseEntity<List<Order>> getCustomerOrders(@PathVariable String customerId) { return ResponseEntity.ok(orderRepository.findByCustomerId(customerId)); } }

2. Monitoring Endpoints

@RestController @RequestMapping("/api/monitoring") @Slf4j public class MonitoringController { private final MeterRegistry meterRegistry; private final List<Neuron> neurons; public MonitoringController(MeterRegistry meterRegistry, List<Neuron> neurons) { this.meterRegistry = meterRegistry; this.neurons = neurons; } @GetMapping("/metrics") public ResponseEntity<Map<String, Object>> getSystemMetrics() { Map<String, Object> metrics = new HashMap<>(); // Neuron metrics Map<String, Object> neuronMetrics = neurons.stream() .collect(Collectors.toMap( Neuron::getNeuronId, neuron -> { NeuronHealth health = neuron.getHealth(); return Map.of( "eventsProcessed", health.getEventsProcessed(), "commandsProcessed", health.getCommandsProcessed(), "eventsPublished", health.getEventsPublished(), "errors", health.getErrors(), "successes", health.getSuccesses(), "errorRate", health.getErrorRate(), "uptime", health.getUptime().toMinutes() ); } )); metrics.put("neurons", neuronMetrics); // System metrics from Micrometer metrics.put("jvm", getJvmMetrics()); metrics.put("system", getSystemMetrics()); return ResponseEntity.ok(metrics); } @GetMapping("/prometheus") public String getPrometheusMetrics() { // Expose metrics in Prometheus format StringBuilder prometheus = new StringBuilder(); for (Neuron neuron : neurons) { NeuronHealth health = neuron.getHealth(); String neuronName = neuron.getNeuronId().replace("-", "_"); prometheus.append(String.format("cortex_neuron_events_processed{neuron=\"%s\"} %d\n", neuron.getNeuronId(), health.getEventsProcessed())); prometheus.append(String.format("cortex_neuron_errors_total{neuron=\"%s\"} %d\n", neuron.getNeuronId(), health.getErrors())); prometheus.append(String.format("cortex_neuron_error_rate{neuron=\"%s\"} %.4f\n", neuron.getNeuronId(), health.getErrorRate())); } return prometheus.toString(); } private Map<String, Object> getJvmMetrics() { return Map.of( "memory", Map.of( "used", Runtime.getRuntime().totalMemory() - Runtime.getRuntime().freeMemory(), "max", Runtime.getRuntime().maxMemory(), "total", Runtime.getRuntime().totalMemory() ), "threads", Thread.activeCount() ); } private Map<String, Object> getSystemMetrics() { return Map.of( "timestamp", LocalDateTime.now(), "uptime", ManagementFactory.getRuntimeMXBean().getUptime() ); } }

Resilience Configuration

@Configuration @Slf4j public class ResilienceConfiguration { @Bean public CircuitBreakerRegistry circuitBreakerRegistry() { return CircuitBreakerRegistry.ofDefaults(); } @Bean public RetryRegistry retryRegistry() { return RetryRegistry.ofDefaults(); } @Bean public BulkheadRegistry bulkheadRegistry() { return BulkheadRegistry.ofDefaults(); } @Bean @EventListener public void onCircuitBreakerEvent(CircuitBreakerOnStateTransitionEvent event) { log.warn("Circuit Breaker {} transitioned to {}", event.getCircuitBreakerName(), event.getStateTransition()); } @Bean @EventListener public void onRetryEvent(RetryOnRetryEvent event) { log.info("Retry attempt {} for {}", event.getNumberOfRetryAttempts(), event.getName()); } } @Component @Slf4j public class CortexResilienceService { private final CircuitBreaker circuitBreaker; private final Retry retry; private final Bulkhead bulkhead; public CortexResilienceService(CircuitBreakerRegistry circuitBreakerRegistry, RetryRegistry retryRegistry, BulkheadRegistry bulkheadRegistry) { this.circuitBreaker = circuitBreakerRegistry.circuitBreaker("cortex-service"); this.retry = retryRegistry.retry("cortex-service"); this.bulkhead = bulkheadRegistry.bulkhead("cortex-service"); } public <T> T executeResilient(Supplier<T> supplier, Function<Throwable, T> fallback) { Supplier<T> decoratedSupplier = Decorators.ofSupplier(supplier) .withCircuitBreaker(circuitBreaker) .withRetry(retry) .withBulkhead(bulkhead) .withFallback(fallback) .decorate(); return Try.ofSupplier(decoratedSupplier) .onSuccess(result -> log.debug("Resilient execution succeeded")) .onFailure(throwable -> log.error("Resilient execution failed", throwable)) .get(); } public void executeResilient(Runnable runnable, Runnable fallback) { CheckedRunnable decoratedRunnable = Decorators.ofCheckedRunnable(runnable::run) .withCircuitBreaker(circuitBreaker) .withRetry(retry) .withBulkhead(bulkhead) .withFallback(throwable -> { log.warn("Executing fallback due to: {}", throwable.getMessage()); fallback.run(); }) .decorate(); Try.run(decoratedRunnable) .onSuccess(result -> log.debug("Resilient execution succeeded")) .onFailure(throwable -> log.error("Resilient execution failed", throwable)); } }

Testing

1. Unit Tests

@ExtendWith(MockitoExtension.class) class ProductNeuronTest { @Mock private CortexEventBus eventBus; @Mock private ProductRepository productRepository; @Mock private AxonEventProcessor axonProcessor; private ProductNeuron productNeuron; @BeforeEach void setUp() { productNeuron = new ProductNeuron(eventBus, productRepository, axonProcessor); } @Test void testHandleProductCreated() { // Given ProductCreatedEvent event = new ProductCreatedEvent( "prod-123", "Test Product", "Description", BigDecimal.valueOf(99.99), 100, "corr-123" ); // When productNeuron.handleEvent(event); // Then verify(productRepository).save(any(Product.class)); verify(eventBus).publish(any(CortexEvent.class)); } } @SpringBootTest class CortexEventBusTest { @Autowired private CortexEventBus eventBus; @Test void testEventPublishing() { // Given AtomicInteger handlerCallCount = new AtomicInteger(0); CortexEventBus.EventHandler handler = event -> handlerCallCount.incrementAndGet(); eventBus.subscribe("TEST_EVENT", handler); // When CortexEvent event = new CortexEvent("corr-123", "test-neuron") { @Override public String getEventType() { return "TEST_EVENT"; } }; eventBus.publish(event); // Then assertThat(handlerCallCount.get()).isEqualTo(1); } }

2. Integration Test

@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT) @TestPropertySource(properties = { "spring.datasource.url=jdbc:h2:mem:testdb", "spring.jpa.hibernate.ddl-auto=create-drop" }) class CortexSystemIntegrationTest { @Autowired private TestRestTemplate restTemplate; @Autowired private ProductRepository productRepository; @Test void testProductCreationFlow() { // Given Map<String, Object> productRequest = Map.of( "name", "Test Product", "description", "Test Description", "price", 99.99, "initialStock", 100 ); // When ResponseEntity<Map> response = restTemplate.postForEntity( "/api/products", productRequest, Map.class); // Then assertThat(response.getStatusCode()).isEqualTo(HttpStatus.ACCEPTED); assertThat(response.getBody()).containsKeys("productId", "correlationId"); // Verify product was created in read model String productId = (String) response.getBody().get("productId"); await().atMost(5, TimeUnit.SECONDS).until(() -> productRepository.findById(productId).isPresent()); Product product = productRepository.findById(productId).orElseThrow(); assertThat(product.getName()).isEqualTo("Test Product"); assertThat(product.getStockQuantity()).isEqualTo(100); } }

Deployment Configuration

# docker-compose.yml version: '3.8' services: cortex-app: build: . ports: - "8080:8080" environment: - SPRING_DATASOURCE_URL=jdbc:postgresql://postgres:5432/cortex - SPRING_KAFKA_BOOTSTRAP_SERVERS=kafka:9092 - SPRING_REDIS_HOST=redis depends_on: - postgres - kafka - redis postgres: image: postgres:15 environment: - POSTGRES_DB=cortex - POSTGRES_USER=postgres - POSTGRES_PASSWORD=password ports: - "5432:5432" kafka: image: confluentinc/cp-kafka:7.3.0 environment: - KAFKA_ZOOKEEPER_CONNECT=zookeeper:2181 - KAFKA_ADVERTISED_LISTENERS=PLAINTEXT://kafka:9092 - KAFKA_OFFSETS_TOPIC_REPLICATION_FACTOR=1 ports: - "9092:9092" depends_on: - zookeeper zookeeper: image: confluentinc/cp-zookeeper:7.3.0 environment: - ZOOKEEPER_CLIENT_PORT=2181 redis: image: redis:7-alpine ports: - "6379:6379" axon-server: image: axoniq/axonserver:latest ports: - "8024:8024" - "8124:8124" environment: - AXONIQ_AXONSERVER_DEVMODE_ENABLED=true prometheus: image: prom/prometheus:latest ports: - "9090:9090" volumes: - ./prometheus.yml:/etc/prometheus/prometheus.yml grafana: image: grafana/grafana:latest ports: - "3000:3000" environment: - GF_SECURITY_ADMIN_PASSWORD=admin

Best Practices

Event Design: Keep events small, focused, and immutable
Error Handling: Implement comprehensive error handling and dead letter queues
Monitoring: Extensive monitoring of all neurons and system components
Testing: Comprehensive testing including unit, integration, and resilience tests
Documentation: Document event schemas and neuron responsibilities
Versioning: Implement event versioning for schema evolution

// Example of event versioning public class ProductCreatedEventV2 extends DomainEvent { private final String productId; private final String name; private final String description; private final BigDecimal price; private final int initialStock; private final String category; // New field in V2 public ProductCreatedEventV2(String productId, String name, String description, BigDecimal price, int initialStock, String category, String correlationId) { super(productId, correlationId, "product-neuron"); this.productId = productId; this.name = name; this.description = description; this.price = price; this.initialStock = initialStock; this.category = category; } @Override public String getEventType() { return "PRODUCT_CREATED_V2"; } // Getters including new category field }

Conclusion

The Cortex architecture provides:

High Scalability through event-driven, asynchronous processing
Resilience with circuit breakers, retries, and fallbacks
Maintainability through clear separation of concerns
Observability with comprehensive monitoring and metrics
Flexibility through modular neuron design
Event Sourcing for complete audit trails and temporal queries

This implementation demonstrates how to build a scalable, resilient system using Cortex architecture principles in Java, suitable for complex enterprise applications requiring high availability and performance.

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