Clustering and Load Balancing

/**
 * Cluster interface for fault tolerance strategies
 */
@SPI(FailoverCluster.NAME)
public interface Cluster {
    /**
     * Join multiple invokers into a cluster
     * @param directory Provider directory
     * @return Cluster invoker
     * @throws RpcException if cluster creation fails
     */
    <T> Invoker<T> join(Directory<T> directory) throws RpcException;
}

/**
 * Failover cluster - automatically failover to other providers when failure occurs
 */
public class FailoverCluster implements Cluster {
    public static final String NAME = "failover";
}

/**
 * Failfast cluster - fail immediately on first error
 */
public class FailfastCluster implements Cluster {
    public static final String NAME = "failfast";
}

/**
 * Failsafe cluster - ignore failures and return empty result
 */
public class FailsafeCluster implements Cluster {
    public static final String NAME = "failsafe";
}

/**
 * Failback cluster - retry failed requests in background
 */
public class FailbackCluster implements Cluster {
    public static final String NAME = "failback";
}

/**
 * Broadcast cluster - broadcast invocation to all providers
 */
public class BroadcastCluster implements Cluster {
    public static final String NAME = "broadcast";
}

/**
 * Forking cluster - parallel invocation, return first successful result
 */
public class ForkingCluster implements Cluster {
    public static final String NAME = "forking";
}

/**
 * Available cluster - call the first available provider
 */
public class AvailableCluster implements Cluster {
    public static final String NAME = "available";
}

/**
 * Mergeable cluster - merge results from multiple providers
 */
public class MergeableCluster implements Cluster {
    public static final String NAME = "mergeable";
}

// Configure cluster strategy in service reference
ReferenceConfig<GreeterService> reference = new ReferenceConfig<>();
reference.setInterface(GreeterService.class);
reference.setCluster("failover"); // Use failover strategy
reference.setRetries(2); // Retry 2 times on failure

// Or configure via URL parameters
reference.setUrl("dubbo://localhost:20880/GreeterService?cluster=failfast");

/**
 * Load balance interface for selecting providers
 */
@SPI(RandomLoadBalance.NAME)
public interface LoadBalance {
    /**
     * Select one invoker from available providers
     * @param invokers Available service providers
     * @param url Service URL with parameters
     * @param invocation RPC invocation context
     * @return Selected invoker
     * @throws RpcException if selection fails
     */
    <T> Invoker<T> select(List<Invoker<T>> invokers, URL url, Invocation invocation) 
        throws RpcException;
}

/**
 * Random load balance - select provider randomly
 */
public class RandomLoadBalance extends AbstractLoadBalance {
    public static final String NAME = "random";
    
    @Override
    protected <T> Invoker<T> doSelect(List<Invoker<T>> invokers, URL url, Invocation invocation) {
        // Implementation selects random provider
        return invokers.get(ThreadLocalRandom.current().nextInt(invokers.size()));
    }
}

/**
 * Round robin load balance - weighted round-robin selection
 */
public class RoundRobinLoadBalance extends AbstractLoadBalance {
    public static final String NAME = "roundrobin";
}

/**
 * Least active load balance - select provider with least active requests
 */
public class LeastActiveLoadBalance extends AbstractLoadBalance {
    public static final String NAME = "leastactive";
}

/**
 * Shortest response load balance - select provider with shortest response time
 */
public class ShortestResponseLoadBalance extends AbstractLoadBalance {
    public static final String NAME = "shortestresponse";
}

/**
 * Consistent hash load balance - consistent hash ring selection
 */
public class ConsistentHashLoadBalance extends AbstractLoadBalance {
    public static final String NAME = "consistenthash";
}

/**
 * Adaptive load balance - select based on adaptive algorithm
 */
public class AdaptiveLoadBalance extends AbstractLoadBalance {
    public static final String NAME = "adaptive";
}

// Configure load balancing in service reference
ReferenceConfig<GreeterService> reference = new ReferenceConfig<>();
reference.setInterface(GreeterService.class);
reference.setLoadbalance("roundrobin"); // Use round-robin load balancing

// Configure per method
MethodConfig method = new MethodConfig();
method.setName("sayHello");
method.setLoadbalance("leastactive");
reference.setMethods(Arrays.asList(method));

// Configure consistent hash with specific hash arguments
reference.setUrl("dubbo://localhost:20880/GreeterService?loadbalance=consistenthash&hash.arguments=0");

/**
 * Provider directory for managing service provider lists
 * @param <T> Service interface type
 */
public interface Directory<T> {
    /** Get service interface class */
    Class<T> getInterface();
    
    /**
     * List available invokers for the invocation
     * @param invocation RPC invocation context
     * @return List of available invokers
     * @throws RpcException if listing fails
     */
    List<Invoker<T>> list(Invocation invocation) throws RpcException;
    
    /** Get all invokers regardless of availability */
    List<Invoker<T>> getAllInvokers();
    
    /** Get directory URL */
    URL getUrl();
    
    /** Check if directory is destroyed */
    boolean isDestroyed();
    
    /** Destroy directory and release resources */
    void destroy();
    
    /** Get consumer URL */
    URL getConsumerUrl();
}

/**
 * Registry-aware directory that subscribes to provider changes
 */
public class RegistryDirectory<T> extends AbstractDirectory<T> implements NotifyListener {
    public RegistryDirectory(Class<T> serviceType, URL url);
    
    /** Subscribe to registry for provider updates */
    public void subscribe(URL url);
    
    /** Unsubscribe from registry */
    public void unsubscribe(URL url);
    
    /** Handle provider change notifications */
    public void notify(List<URL> urls);
    
    /** Refresh provider list */
    protected void refreshInvoker(List<URL> invokerUrls);
}

/**
 * Static directory with fixed provider list
 */
public class StaticDirectory<T> extends AbstractDirectory<T> {
    public StaticDirectory(List<Invoker<T>> invokers);
    public StaticDirectory(URL url, List<Invoker<T>> invokers);
}

/**
 * Router interface for filtering and sorting providers
 */
@SPI
public interface Router extends Comparable<Router> {
    /** Get router URL */
    URL getUrl();
    
    /**
     * Route providers based on rules
     * @param invokers Available providers
     * @param url Consumer URL
     * @param invocation RPC invocation
     * @return Filtered providers
     * @throws RpcException if routing fails
     */
    <T> List<Invoker<T>> route(List<Invoker<T>> invokers, URL url, Invocation invocation) 
        throws RpcException;
    
    /** Check if routing is required for this invocation */
    boolean isRuntime();
    
    /** Check if router should be forced to execute */
    boolean isForce();
    
    /** Get router priority (lower value = higher priority) */
    int getPriority();
}

/**
 * Router chain for managing multiple routers
 */
public class RouterChain<T> {
    public RouterChain(URL url);
    
    /** Add router to chain */
    public void addRouter(Router router);
    
    /** Remove router from chain */
    public void removeRouter(Router router);
    
    /** Route through all routers in chain */
    public List<Invoker<T>> route(URL url, Invocation invocation);
    
    /** Set invokers for routing */
    public void setInvokers(List<Invoker<T>> invokers);
}

/**
 * Condition router based on rules
 */
public class ConditionRouter implements Router {
    public ConditionRouter(URL url);
    
    /** Parse routing conditions */
    protected void parseRule(String rule);
}

/**
 * Script router using JavaScript expressions
 */
public class ScriptRouter implements Router {
    public ScriptRouter(URL url);
}

/**
 * File-based router loading rules from files
 */
public class FileRouter implements Router {
    public FileRouter(URL url);
}

/**
 * Tag router for routing based on request tags
 */
public class TagRouter implements Router {
    public TagRouter(URL url);
}

// Condition router rule examples
// Route requests with parameter "user" = "admin" to providers in group "admin"
String rule = "user = admin => group = admin";

// Route all requests during 9-17 hours to specific providers
String timeRule = "=> host = 192.168.1.10,192.168.1.11";

// Configure router in consumer
reference.setUrl("dubbo://localhost:20880/GreeterService?router=condition&rule=" + 
                URLEncoder.encode(rule, "UTF-8"));

/**
 * Configurator interface for dynamic configuration
 */
@SPI
public interface Configurator extends Comparable<Configurator> {
    /** Get configurator URL */
    URL getUrl();
    
    /**
     * Configure URL with dynamic rules
     * @param url Original URL
     * @return Configured URL
     */
    URL configure(URL url);
}

/**
 * Factory for creating configurators
 */
@SPI("override")
public interface ConfiguratorFactory {
    /**
     * Create configurator from URL
     * @param url Configuration URL
     * @return Configurator instance
     */
    Configurator getConfigurator(URL url);
}

/**
 * Override configurator for parameter overrides
 */
public class OverrideConfigurator implements Configurator {
    public OverrideConfigurator(URL url);
    
    @Override
    public URL configure(URL url) {
        // Apply parameter overrides
        return url.addParameters(getUrl().getParameters());
    }
}

/**
 * Absent configurator for conditional configuration
 */
public class AbsentConfigurator implements Configurator {
    public AbsentConfigurator(URL url);
}

/**
 * Abstract cluster invoker providing common cluster functionality
 * @param <T> Service interface type
 */
public abstract class AbstractClusterInvoker<T> implements Invoker<T> {
    protected AbstractClusterInvoker(Directory<T> directory);
    protected AbstractClusterInvoker(Directory<T> directory, URL url);
    
    /** Get provider directory */
    public Directory<T> getDirectory();
    
    /** Get cluster URL */
    public URL getUrl();
    
    /** Check if invoker is available */
    public boolean isAvailable();
    
    /** Destroy cluster invoker */
    public void destroy();
    
    /**
     * List available invokers with load balancing
     * @param invocation RPC invocation
     * @param loadbalance Load balance algorithm
     * @return Selected invoker
     * @throws RpcException if no invoker available
     */
    protected List<Invoker<T>> list(Invocation invocation) throws RpcException;
    
    /**
     * Select invoker using load balance
     * @param loadbalance Load balance algorithm
     * @param invocation RPC invocation
     * @param invokers Available invokers
     * @param selected Previously selected invokers (for retry)
     * @return Selected invoker
     */
    protected Invoker<T> select(LoadBalance loadbalance, Invocation invocation, 
                               List<Invoker<T>> invokers, List<Invoker<T>> selected) 
                               throws RpcException;
    
    /**
     * Template method for cluster-specific invocation
     * @param invocation RPC invocation
     * @return Invocation result
     * @throws RpcException if invocation fails
     */
    protected abstract Result doInvoke(Invocation invocation, List<Invoker<T>> invokers, 
                                      LoadBalance loadbalance) throws RpcException;
}

/**
 * Sticky session management for consistent provider selection
 */
public class StickyUtils {
    /**
     * Get sticky invoker for the invocation
     * @param invokers Available invokers
     * @param invocation Current invocation
     * @param stickyInvoker Previously selected sticky invoker
     * @return Sticky invoker if available and sticky
     */
    public static <T> Invoker<T> getSticky(List<Invoker<T>> invokers, 
                                          Invocation invocation, 
                                          Invoker<T> stickyInvoker) {
        // Return sticky invoker if still available and sticky is enabled
        if (stickyInvoker != null && invokers.contains(stickyInvoker) && 
            isSticky(invocation)) {
            return stickyInvoker;
        }
        return null;
    }
    
    /** Check if sticky session is enabled for invocation */
    private static boolean isSticky(Invocation invocation) {
        String sticky = invocation.getAttachment(STICKY_KEY);
        return "true".equals(sticky);
    }
}

// Enable sticky sessions in service reference
ReferenceConfig<GreeterService> reference = new ReferenceConfig<>();
reference.setInterface(GreeterService.class);
reference.setSticky(true); // Enable sticky sessions

// Configure sticky per method
MethodConfig method = new MethodConfig();
method.setName("sayHello");
method.setSticky(true);
reference.setMethods(Arrays.asList(method));

// Set sticky attachment manually
RpcContext.getContext().setAttachment("sticky", "true");
String result = greeterService.sayHello("World");

/**
 * Constants for fault tolerance configuration
 */
public class ClusterConstants {
    /** Cluster fault tolerance strategy */
    public static final String CLUSTER_KEY = "cluster";
    
    /** Load balance algorithm */
    public static final String LOADBALANCE_KEY = "loadbalance";
    
    /** Sticky session */
    public static final String STICKY_KEY = "sticky";
    
    /** Retry times */
    public static final String RETRIES_KEY = "retries";
    
    /** Fail strategy */
    public static final String FAIL_KEY = "fail";
    
    /** Fork count for forking cluster */
    public static final String FORKS_KEY = "forks";
    
    /** Default retry times */
    public static final int DEFAULT_RETRIES = 2;
    
    /** Default fork count */
    public static final int DEFAULT_FORKS = 2;
}

// Configure comprehensive fault tolerance
ReferenceConfig<GreeterService> reference = new ReferenceConfig<>();
reference.setInterface(GreeterService.class);
reference.setCluster("failover");      // Automatic failover
reference.setLoadbalance("roundrobin"); // Round-robin load balancing
reference.setRetries(3);               // Retry 3 times on failure
reference.setTimeout(5000);            // 5 second timeout
reference.setConnections(5);           // 5 connections per provider

// Method-specific fault tolerance
MethodConfig criticalMethod = new MethodConfig();
criticalMethod.setName("processOrder");
criticalMethod.setCluster("failfast");  // Fail immediately for critical operations
criticalMethod.setTimeout(10000);      // Longer timeout for critical operations
criticalMethod.setRetries(0);          // No retries for critical operations

reference.setMethods(Arrays.asList(criticalMethod));