Synchronization & Consistency

During FGA migration, you’ll often have multiple enforcement methods running simultaneously—network gateways protecting APIs, database proxies securing data access, and library integrations in modernized applications. Maintaining consistent authorization decisions across all these systems is critical for security and user experience.

The Consistency Challenge

🔄 Multi-Method Enforcement

Different enforcement methods may need to make authorization decisions for the same user action:

graph TB
    U[User Request] --> GW[Network Gateway]
    GW --> APP[Application] 
    APP --> LIB[Library Integration]
    LIB --> DB[Database Proxy]
    DB --> DATA[Database]
    
    GW --> FGA[FGA Policy Engine]
    LIB --> FGA
    DB --> FGA
    
    FGA --> SYNC[Sync Manager]

All three enforcement points must agree on authorization decisions to prevent security gaps or access inconsistencies.

⚡ Real-Time Updates

When authorization data changes, all enforcement methods must be updated immediately:

• User role changes: New permissions must propagate instantly
• Policy updates: Modified authorization logic needs coordination
• Resource modifications: Changed resource attributes affect access decisions
• Emergency revocations: Security incidents require immediate access removal

Synchronization Architecture

🎛️ Central Policy Coordination

All enforcement methods connect to a central policy management system:

# Central policy coordination configuration
policy_coordination:
  central_authority: "authonomy-policy-manager"
  enforcement_methods:
    - type: "network_gateway"
      instances: ["gw-01", "gw-02", "gw-03"]
      sync_interval: "5s"
      
    - type: "database_proxy"  
      instances: ["db-proxy-east", "db-proxy-west"]
      sync_interval: "10s"
      
    - type: "library_integration"
      applications: ["web-app", "mobile-api", "admin-portal"]
      sync_method: "webhook"
      
  consistency_guarantees:
    max_propagation_delay: "30s"
    consistency_level: "eventual"
    conflict_resolution: "latest_wins"

🔄 Change Data Capture (CDC)

Real-time synchronization of authorization data:

# CDC configuration for authorization changes
cdc_sources:
  # User management system
  - source: "postgresql://hr.company.com/employees"
    tables: ["employees", "departments", "roles"]
    triggers: ["INSERT", "UPDATE", "DELETE"]
    
  # Legacy authorization database
  - source: "mysql://auth.legacy.com/permissions"
    tables: ["user_roles", "role_permissions", "custom_access"]
    triggers: ["INSERT", "UPDATE", "DELETE"]
    
  # Modern identity provider
  - source: "okta_api"
    resources: ["users", "groups", "applications"]  
    sync_method: "webhook"
    
sync_targets:
  - all_enforcement_methods
  - policy_audit_log
  - compliance_system

📡 Event-Driven Updates

Push authorization changes to all enforcement methods:

// Event-driven policy synchronization
class PolicySyncManager {
  async onAuthorizationChange(event) {
    const { type, resource, change_details } = event;
    
    // Determine affected enforcement methods
    const affectedMethods = this.findAffectedMethods(resource);
    
    // Prepare synchronization tasks
    const syncTasks = affectedMethods.map(method => 
      this.syncMethod(method, change_details)
    );
    
    // Execute synchronization in parallel
    const results = await Promise.allSettled(syncTasks);
    
    // Handle any synchronization failures
    const failures = results.filter(r => r.status === 'rejected');
    if (failures.length > 0) {
      await this.handleSyncFailures(failures, event);
    }
    
    // Verify consistency across all methods
    await this.verifyConsistency(resource);
  }
}

Consistency Models

📏 Strong Consistency

All enforcement methods see the same authorization state simultaneously:

# Strong consistency configuration
consistency:
  model: "strong"
  coordination: "distributed_lock"
  
  requirements:
    max_latency: "100ms"
    availability: "99.9%"
    
  implementation:
    consensus_protocol: "raft"
    minimum_replicas: 3
    
  use_cases:
    - financial_transactions
    - medical_record_access
    - regulatory_compliance

Benefits: Perfect consistency, no authorization conflicts Trade-offs: Higher latency, more complex infrastructure

🌊 Eventual Consistency

Authorization changes propagate within defined time windows:

# Eventual consistency configuration  
consistency:
  model: "eventual"
  propagation_window: "30s"
  
  conflict_resolution:
    strategy: "latest_timestamp_wins"
    rollback_capability: true
    
  monitoring:
    convergence_time: "< 30s"
    consistency_violations: "< 0.1%"
    
  use_cases:
    - content_management_systems
    - customer_support_portals
    - internal_dashboards

Benefits: Better performance and availability Trade-offs: Temporary inconsistencies possible

⚖️ Hybrid Consistency

Different consistency levels for different resource types:

# Hybrid consistency strategy
consistency_policies:
  high_security:
    resources: ["payment_data", "medical_records"]
    consistency: "strong"
    max_latency: "50ms"
    
  standard_security:
    resources: ["customer_profiles", "order_history"] 
    consistency: "eventual"
    propagation_window: "30s"
    
  low_security:
    resources: ["product_catalogs", "marketing_content"]
    consistency: "eventual" 
    propagation_window: "5m"

Conflict Resolution

🤝 Conflict Detection

Identify when different enforcement methods have inconsistent state:

// Conflict detection example
class ConsistencyMonitor {
  async checkConsistency(user, resource, action) {
    const decisions = await Promise.all([
      this.networkGateway.check(user, action, resource),
      this.databaseProxy.check(user, action, resource), 
      this.libraryIntegration.check(user, action, resource)
    ]);
    
    // Check for decision conflicts
    const allowDecisions = decisions.filter(d => d.allowed);
    const denyDecisions = decisions.filter(d => !d.allowed);
    
    if (allowDecisions.length > 0 && denyDecisions.length > 0) {
      // Conflict detected
      await this.handleAuthorizationConflict({
        user, resource, action,
        decisions,
        conflict_type: "mixed_decisions"
      });
    }
    
    return {
      consistent: decisions.every(d => d.allowed === decisions[0].allowed),
      decisions: decisions
    };
  }
}

⚡ Automatic Resolution

Resolve conflicts using predefined strategies:

# Conflict resolution strategies
conflict_resolution:
  strategies:
    # Security-first: Deny wins
    - name: "deny_wins"
      description: "If any enforcement method denies, the final decision is deny"
      use_cases: ["high_security_systems"]
      
    # Availability-first: Allow wins  
    - name: "allow_wins"
      description: "If any enforcement method allows, the final decision is allow"
      use_cases: ["development_environments"]
      
    # Timestamp-based: Latest wins
    - name: "latest_timestamp_wins"
      description: "Most recent policy decision takes precedence"
      use_cases: ["policy_updates"]
      
    # Hierarchy-based: Priority order
    - name: "enforcement_hierarchy"
      priority_order: ["library_integration", "database_proxy", "network_gateway"]
      description: "Higher priority enforcement method wins conflicts"

🚨 Manual Intervention

Some conflicts require human decision:

# Manual resolution workflow
manual_resolution:
  triggers:
    - security_level: "critical"
      auto_resolution_failed: true
      
  workflow:
    - notify: ["security_team", "on_call_engineer"]
    - create_incident: "authorization_conflict"
    - temporary_action: "deny_access"  # Fail securely
    - resolution_sla: "15_minutes"
    
  escalation:
    - after: "15_minutes"
      notify: ["security_manager"] 
    - after: "30_minutes"
      notify: ["ciso"]

Implementation Patterns

🔄 Bidirectional Synchronization

Keep authorization data synchronized between legacy and modern systems:

// Bidirectional sync implementation
class BidirectionalSync {
  async syncUserRoleChange(user, newRoles) {
    // Update modern FGA system
    await this.fgaClient.updateUserRoles(user.id, newRoles);
    
    // Update legacy systems that haven't migrated yet
    const legacySystems = await this.getLegacySystemsForUser(user);
    
    const syncPromises = legacySystems.map(system => 
      this.updateLegacyUserRoles(system, user.id, newRoles)
    );
    
    // Wait for all updates to complete
    const results = await Promise.allSettled(syncPromises);
    
    // Handle any failures
    const failures = results.filter(r => r.status === 'rejected');
    if (failures.length > 0) {
      await this.handleLegacySyncFailures(user, newRoles, failures);
    }
  }
}

🎯 Selective Synchronization

Sync only relevant changes to minimize overhead:

# Selective sync configuration
sync_rules:
  user_role_changes:
    sync_to: ["all_enforcement_methods"]
    priority: "immediate"
    
  policy_updates:
    sync_to: ["affected_enforcement_methods"]
    priority: "high"
    batch_size: 100
    
  resource_metadata:
    sync_to: ["enforcement_methods_using_resource"]
    priority: "normal"
    batch_interval: "5m"
    
  audit_logs:
    sync_to: ["compliance_systems"] 
    priority: "low"
    batch_interval: "1h"

Performance Optimization

⚡ Synchronization Batching

Group related changes to reduce overhead:

// Batch synchronization for performance
class BatchSyncManager {
  private pendingChanges = new Map();
  private batchTimeout = null;
  
  async queueChange(change) {
    const key = `${change.resource_type}:${change.resource_id}`;
    
    // Accumulate changes for the same resource
    if (!this.pendingChanges.has(key)) {
      this.pendingChanges.set(key, []);
    }
    this.pendingChanges.get(key).push(change);
    
    // Schedule batch processing
    if (!this.batchTimeout) {
      this.batchTimeout = setTimeout(() => this.processBatch(), 5000);
    }
  }
  
  async processBatch() {
    const changes = Array.from(this.pendingChanges.entries());
    this.pendingChanges.clear();
    this.batchTimeout = null;
    
    // Process all changes in parallel
    await Promise.all(
      changes.map(([resource, changeList]) => 
        this.syncResourceChanges(resource, changeList)
      )
    );
  }
}

🏃 Async Synchronization

Non-blocking updates for better performance:

// Asynchronous synchronization
async function updateAuthorization(user, resource, change) {
  // Update primary enforcement method immediately
  const primaryResult = await primaryEnforcement.update(user, resource, change);
  
  // Sync to other methods asynchronously
  setImmediate(() => {
    syncToSecondaryMethods(user, resource, change)
      .catch(error => logger.error('Secondary sync failed:', error));
  });
  
  return primaryResult;
}

Monitoring & Alerting

📊 Consistency Monitoring

Track synchronization health across all enforcement methods:

# Consistency monitoring configuration
monitoring:
  metrics:
    - name: "sync_latency"
      type: "histogram"
      labels: ["source_method", "target_method", "change_type"]
      
    - name: "consistency_violations"  
      type: "counter"
      labels: ["resource_type", "violation_type"]
      
    - name: "sync_queue_depth"
      type: "gauge"
      labels: ["enforcement_method"]
      
  alerts:
    - name: "high_sync_latency"
      condition: "sync_latency_p95 > 30s"
      severity: "warning"
      
    - name: "consistency_violation"
      condition: "consistency_violations > 0"
      severity: "critical"
      
    - name: "sync_queue_backup"
      condition: "sync_queue_depth > 1000"
      severity: "warning"

🚨 Drift Detection

Automatically detect when enforcement methods diverge:

// Consistency drift detection
class DriftDetector {
  async detectDrift() {
    const sampleRequests = await this.generateTestRequests();
    
    for (const request of sampleRequests) {
      const decisions = await Promise.all([
        this.networkGateway.authorize(request),
        this.databaseProxy.authorize(request),
        this.libraryIntegration.authorize(request)
      ]);
      
      // Check for decision consistency
      const allowCount = decisions.filter(d => d.allowed).length;
      const totalCount = decisions.length;
      
      if (allowCount > 0 && allowCount < totalCount) {
        await this.reportDrift({
          request,
          decisions,
          drift_type: "partial_consistency",
          severity: this.calculateSeverity(request)
        });
      }
    }
  }
}

Advanced Synchronization Patterns

🎭 Master-Slave Replication

Designate primary enforcement method with secondary replicas:

# Master-slave configuration
replication:
  master: "library_integration"
  slaves: ["network_gateway", "database_proxy"]
  
  replication_mode: "async"
  lag_tolerance: "5s"
  
  failure_handling:
    master_failure: "promote_slave"
    slave_failure: "continue_with_master"
    
  consistency_checks:
    frequency: "hourly"
    sample_size: 1000

🌐 Multi-Region Synchronization

Coordinate authorization across geographic regions:

# Multi-region sync configuration
regions:
  us_east:
    enforcement_methods: ["gateway_use1", "db_proxy_use1"]
    primary_region: true
    
  eu_west:
    enforcement_methods: ["gateway_euw1", "db_proxy_euw1"]  
    replication_source: "us_east"
    lag_tolerance: "100ms"
    
  asia_pacific:
    enforcement_methods: ["gateway_apse1"]
    replication_source: "us_east"
    lag_tolerance: "200ms"

global_policies:
  - name: "admin_access"
    replicate_to: "all_regions"
    
  - name: "regional_data_access"
    replicate_to: "region_specific"

🔄 Cross-System Transactions

Ensure authorization changes are atomic across multiple systems:

// Distributed transaction for authorization updates
async function updateUserPermissionsAtomic(userId, newPermissions) {
  const transaction = new DistributedTransaction();
  
  try {
    // Start transaction across all enforcement methods
    await transaction.begin([
      'network_gateway',
      'database_proxy', 
      'library_integration'
    ]);
    
    // Update permissions in all systems
    await transaction.execute('network_gateway', 
      () => networkGateway.updateUserPermissions(userId, newPermissions));
      
    await transaction.execute('database_proxy',
      () => databaseProxy.updateUserPermissions(userId, newPermissions));
      
    await transaction.execute('library_integration',
      () => libraryIntegration.updateUserPermissions(userId, newPermissions));
    
    // Commit if all updates succeeded
    await transaction.commit();
    
  } catch (error) {
    // Rollback on any failure
    await transaction.rollback();
    throw new AuthorizationSyncError(`Failed to update permissions: ${error.message}`);
  }
}

Handling Legacy System Constraints

🐌 Slow Legacy Updates

Some legacy systems can’t be updated in real-time:

# Mixed synchronization speeds
sync_strategies:
  real_time:
    methods: ["network_gateway", "library_integration"]
    latency: "< 1s"
    
  batch_sync:
    methods: ["legacy_mainframe", "old_database_system"]
    interval: "15m"
    batch_size: 500
    
  manual_sync:
    methods: ["paper_based_approvals", "air_gapped_systems"]
    process: "export_import" 
    frequency: "daily"

🔄 Compensation Patterns

Handle temporary inconsistencies gracefully:

// Compensation for slow legacy sync
async function handleSlowLegacySync(change) {
  // Update fast systems immediately
  await Promise.all([
    fastMethods.map(method => method.applyChange(change))
  ]);
  
  // Queue change for slow systems
  await slowSyncQueue.enqueue(change);
  
  // Create temporary compensation rules
  if (change.requires_immediate_effect) {
    await temporaryRules.create({
      user: change.user,
      resource: change.resource, 
      temporary_access: change.grants_access,
      expires_at: Date.now() + (30 * 60 * 1000), // 30 minutes
      reason: "legacy_sync_delay"
    });
  }
}

Migration-Specific Synchronization

🚀 Gradual Rollout Coordination

Coordinate enforcement across systems during migration:

# Migration synchronization phases
migration_sync:
  phase_1:
    name: "shadow_mode_all"
    enforcement: "none"  # All methods in shadow mode
    sync_requirement: "immediate"
    
  phase_2:
    name: "gateway_enforcement"
    enforcement: 
      network_gateway: "active"
      database_proxy: "shadow" 
      library_integration: "shadow"
    sync_requirement: "strong_consistency"
    
  phase_3:
    name: "full_enforcement"
    enforcement: "active"  # All methods enforcing
    sync_requirement: "eventual_consistency"

🎯 Feature Flag Coordination

Synchronize feature flag states across enforcement methods:

// Feature flag synchronization
class FeatureFlagSync {
  async updateFeatureFlag(flagName, enabled, scope) {
    const enforcementMethods = this.getEnforcementMethodsInScope(scope);
    
    // Update all relevant enforcement methods
    const updatePromises = enforcementMethods.map(method =>
      method.updateFeatureFlag(flagName, enabled)
    );
    
    const results = await Promise.allSettled(updatePromises);
    
    // Verify all updates succeeded
    const failures = results.filter(r => r.status === 'rejected');
    if (failures.length > 0) {
      // Rollback successful updates
      await this.rollbackFeatureFlag(flagName, !enabled, scope);
      throw new FeatureFlagSyncError('Failed to sync feature flag');
    }
  }
}

Best Practices

✅ Synchronization Guidelines

• Start with eventual consistency: Perfect for most scenarios, easier to implement
• Use strong consistency sparingly: Only for critical security decisions
• Monitor drift proactively: Regular consistency checks prevent problems
• Plan for failures: Always have rollback and recovery procedures

🔒 Security Considerations

• Encrypt synchronization traffic: All sync communication must be secured
• Authenticate sync sources: Verify sync requests are legitimate
• Audit sync operations: Log all authorization changes for compliance
• Rate limit sync operations: Prevent synchronization flooding

📈 Performance Tips

• Batch related changes: Group updates for efficiency
• Use async patterns: Don’t block user requests for synchronization
• Implement smart routing: Send changes only to affected enforcement methods
• Cache sync state: Reduce redundant synchronization operations

Troubleshooting Guide

🚨 Common Issues

Synchronization Lag

• Check network connectivity between enforcement methods
• Verify sync queue depths and processing rates
• Review batch sizes and intervals
• Consider increasing sync worker capacity

Decision Inconsistencies

• Validate policy versions across all enforcement methods
• Check for conflicting local policy overrides
• Review user context data synchronization
• Verify clock synchronization across systems

Sync Failures

• Check authentication credentials for sync operations
• Verify network connectivity and firewall rules
• Review error logs for specific failure causes
• Test sync operations manually to isolate issues

Implementation Checklist

✅ Pre-Migration Sync Setup

• Central policy coordination service deployed
• CDC configured for all authorization data sources
• Sync monitoring and alerting configured
• Consistency validation tests implemented

✅ During Migration

• Shadow mode consistency validation active
• Drift detection running continuously
• Manual resolution procedures documented and tested
• Rollback procedures validated and ready

✅ Post-Migration

• All enforcement methods synchronized and consistent
• Legacy synchronization connections removed
• Consistency monitoring optimized for production load
• Documentation updated with final sync architecture

Next Steps

With synchronization and consistency in place, review the complete Migration Methodology to understand the full end-to-end process, or explore advanced Policy Management techniques.

Need help designing your synchronization architecture? Contact our platform architects for guidance on consistency strategies for your specific infrastructure.