High Availability Storage

/**
 * Persistent store for Mesos worker state and framework information
 * Provides fault tolerance and state recovery for high availability deployments
 */
public interface MesosWorkerStore {
    /**
     * Initialize the worker store and establish connections
     * Must be called before any other operations
     * @throws Exception if the worker store cannot be started
     */
    void start() throws Exception;
    
    /**
     * Stop the worker store and cleanup resources
     * @param cleanup - Whether to perform cleanup operations (remove stored data)
     * @throws Exception if the worker store cannot be stopped properly
     */
    void stop(boolean cleanup) throws Exception;
    
    /**
     * Get the stored Mesos framework ID for framework re-registration
     * @return Optional framework ID, empty if none stored
     * @throws Exception if the framework ID cannot be retrieved
     */
    Option<Protos.FrameworkID> getFrameworkID() throws Exception;
    
    /**
     * Store the Mesos framework ID for persistent framework identity
     * @param frameworkID - Framework ID to store, or empty to clear
     * @throws Exception if the framework ID cannot be stored
     */
    void setFrameworkID(Option<Protos.FrameworkID> frameworkID) throws Exception;
    
    /**
     * Recover all stored worker information after restart
     * Used during framework recovery to restore cluster state
     * @return List of all stored workers with their current state
     * @throws Exception if worker information cannot be recovered
     */
    List<Worker> recoverWorkers() throws Exception;
    
    /**
     * Generate a new unique task ID for worker identification
     * Ensures task ID uniqueness across framework restarts
     * @return New unique Mesos task ID
     * @throws Exception if a new task ID cannot be generated
     */
    Protos.TaskID newTaskID() throws Exception;
    
    /**
     * Store worker information persistently
     * Updates existing worker if task ID already exists
     * @param worker - Worker information to store
     * @throws Exception if the worker cannot be stored
     */
    void putWorker(Worker worker) throws Exception;
    
    /**
     * Remove worker from persistent storage
     * @param taskID - Task ID of worker to remove
     * @return true if worker was found and removed, false otherwise
     * @throws Exception if the worker cannot be removed
     */
    boolean removeWorker(Protos.TaskID taskID) throws Exception;
}

/**
 * Stored worker representation with state and launch information
 * Contains all information needed to recover worker after framework restart
 */
public static class Worker implements Serializable {
    /**
     * Create worker entry for storage
     * @param taskId - Unique Mesos task ID
     * @param launchableWorker - Worker launch specification
     * @param state - Current worker lifecycle state
     */
    public Worker(Protos.TaskID taskId, 
                  LaunchableMesosWorker launchableWorker, 
                  WorkerState state);
    
    /**
     * Get the Mesos task ID for this worker
     * @return Unique task identifier
     */
    public Protos.TaskID taskID();
    
    /**
     * Get the launchable worker specification
     * @return Worker launch configuration and requirements
     */
    public LaunchableMesosWorker launchableMesosWorker();
    
    /**
     * Get the current worker lifecycle state
     * @return Current state in worker lifecycle
     */
    public WorkerState state();
    
    /**
     * Create a new worker with updated state
     * @param newState - New lifecycle state
     * @return New Worker instance with updated state
     */
    public Worker withState(WorkerState newState);
}

/**
 * Worker lifecycle states for state machine management
 */
public enum WorkerState {
    /** Worker created but not yet launched */
    New,
    /** Worker successfully launched on Mesos slave */
    Launched,
    /** Worker released and no longer active */
    Released
}

import org.apache.flink.mesos.runtime.clusterframework.store.MesosWorkerStore;
import org.apache.flink.mesos.runtime.clusterframework.store.MesosWorkerStore.Worker;
import org.apache.flink.mesos.runtime.clusterframework.store.MesosWorkerStore.WorkerState;

// Store new worker
MesosWorkerStore store = /* ... */;
Protos.TaskID taskId = store.newTaskID();
LaunchableMesosWorker launchableWorker = /* ... */;

Worker newWorker = new Worker(taskId, launchableWorker, WorkerState.New);
store.putWorker(newWorker);

// Update worker state after successful launch
Worker launchedWorker = newWorker.withState(WorkerState.Launched);
store.putWorker(launchedWorker);

// Remove worker when no longer needed
store.removeWorker(taskId);

/**
 * In-memory implementation of MesosWorkerStore for standalone deployments
 * Data is not persisted across process restarts - suitable for development only
 */
public class StandaloneMesosWorkerStore implements MesosWorkerStore {
    /**
     * Create standalone worker store with configuration
     * @param config - Flink configuration (unused in standalone mode)
     */
    public StandaloneMesosWorkerStore(Configuration config);
    
    // Implements all MesosWorkerStore interface methods
    // Data stored in memory only - lost on restart
}

/**
 * ZooKeeper-based implementation of MesosWorkerStore for high availability
 * Provides persistent storage with automatic failover and consistency guarantees
 */
public class ZooKeeperMesosWorkerStore implements MesosWorkerStore {
    /**
     * Create ZooKeeper-based worker store
     * @param curatorFramework - ZooKeeper client framework
     * @param configuration - Flink configuration with ZK settings
     */
    public ZooKeeperMesosWorkerStore(CuratorFramework curatorFramework, 
                                     Configuration configuration);
    
    // Implements all MesosWorkerStore interface methods
    // Data persisted in ZooKeeper with automatic replication
}

import org.apache.flink.configuration.Configuration;
import org.apache.flink.mesos.runtime.clusterframework.store.ZooKeeperMesosWorkerStore;
import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.CuratorFrameworkFactory;

// Configure ZooKeeper connection
Configuration config = new Configuration();
config.setString("high-availability", "zookeeper");
config.setString("high-availability.zookeeper.quorum", "zk1:2181,zk2:2181,zk3:2181");
config.setString("high-availability.zookeeper.path.root", "/flink");
config.setString("high-availability.cluster-id", "production-cluster-1");

// Create ZooKeeper client
CuratorFramework curator = CuratorFrameworkFactory.newClient(
    "zk1:2181,zk2:2181,zk3:2181",
    new ExponentialBackoffRetry(1000, 3)
);
curator.start();

// Create HA worker store
ZooKeeperMesosWorkerStore store = new ZooKeeperMesosWorkerStore(curator, config);
store.start();

import org.apache.flink.mesos.runtime.clusterframework.store.MesosWorkerStore;

// Framework recovery procedure
public void recoverFrameworkState(MesosWorkerStore store) {
    // Recover framework ID for re-registration
    Option<Protos.FrameworkID> frameworkId = store.getFrameworkID();
    
    if (frameworkId.isDefined()) {
        // Re-register with existing framework ID
        reregisterFramework(frameworkId.get());
    } else {
        // Fresh registration - first time startup
        registerNewFramework();
    }
    
    // Recover all workers and their states
    List<MesosWorkerStore.Worker> workers = store.recoverWorkers();
    
    for (MesosWorkerStore.Worker worker : workers) {
        switch (worker.state()) {
            case New:
                // Worker was created but never launched - retry launch
                retryWorkerLaunch(worker);
                break;
            case Launched:
                // Worker was launched - verify status and reconcile
                reconcileWorkerState(worker);
                break;
            case Released:
                // Worker was released - clean up if needed
                cleanupReleasedWorker(worker);
                break;
        }
    }
}

// Synchronized worker lifecycle management
public class WorkerLifecycleManager {
    private final MesosWorkerStore store;
    
    public void launchWorker(LaunchableMesosWorker launchableWorker) {
        // Create task ID and store initial state
        Protos.TaskID taskId = store.newTaskID();
        MesosWorkerStore.Worker worker = new MesosWorkerStore.Worker(
            taskId, launchableWorker, WorkerState.New
        );
        store.putWorker(worker);
        
        try {
            // Attempt to launch worker
            launchWorkerOnMesos(launchableWorker);
            
            // Update state to launched on success
            store.putWorker(worker.withState(WorkerState.Launched));
            
        } catch (Exception e) {
            // Remove worker on launch failure
            store.removeWorker(taskId);
            throw e;
        }
    }
    
    public void releaseWorker(Protos.TaskID taskId) {
        // Get current worker state
        List<MesosWorkerStore.Worker> workers = store.recoverWorkers();
        MesosWorkerStore.Worker worker = findWorkerById(workers, taskId);
        
        if (worker != null) {
            // Update state to released
            store.putWorker(worker.withState(WorkerState.Released));
            
            // Perform cleanup after state update
            cleanupWorkerResources(worker);
            
            // Remove from store after successful cleanup
            store.removeWorker(taskId);
        }
    }
}

// Backup framework state
public void backupFrameworkState(MesosWorkerStore store, String backupLocation) {
    // Get all persistent state
    Option<Protos.FrameworkID> frameworkId = store.getFrameworkID();
    List<MesosWorkerStore.Worker> workers = store.recoverWorkers();
    
    // Create backup data structure
    FrameworkBackup backup = new FrameworkBackup(frameworkId, workers, System.currentTimeMillis());
    
    // Serialize and store backup
    writeBackupToStorage(backup, backupLocation);
}

// Restore framework state from backup
public void restoreFrameworkState(MesosWorkerStore store, String backupLocation) {
    // Load backup data
    FrameworkBackup backup = readBackupFromStorage(backupLocation);
    
    // Restore framework ID
    if (backup.getFrameworkId().isDefined()) {
        store.setFrameworkID(backup.getFrameworkId());
    }
    
    // Restore worker states
    for (MesosWorkerStore.Worker worker : backup.getWorkers()) {
        store.putWorker(worker);
    }
}

// Batch worker state updates
public void updateWorkerStates(Map<Protos.TaskID, WorkerState> stateUpdates) {
    List<MesosWorkerStore.Worker> workers = store.recoverWorkers();
    
    // Batch update all workers
    for (Map.Entry<Protos.TaskID, WorkerState> entry : stateUpdates.entrySet()) {
        MesosWorkerStore.Worker worker = findWorkerById(workers, entry.getKey());
        if (worker != null) {
            store.putWorker(worker.withState(entry.getValue()));
        }
    }
}

/**
 * Framework backup data structure
 */
public class FrameworkBackup implements Serializable {
    public Option<Protos.FrameworkID> getFrameworkId();
    public List<MesosWorkerStore.Worker> getWorkers();
    public long getTimestamp();
    public String getVersion();
}

/**
 * Storage configuration for HA deployments
 */
public class HAStorageConfiguration {
    public String getStorageType(); // "standalone" or "zookeeper"
    public String getZooKeeperQuorum();
    public String getStoragePath();
    public int getConnectionTimeout();
    public int getSessionTimeout();
}

/**
 * Worker recovery information
 */
public class WorkerRecoveryInfo {
    public Protos.TaskID getTaskId();
    public WorkerState getLastKnownState();
    public long getLastUpdateTime();
    public boolean requiresReconciliation();
}