As businesses scale and adopt distributed system architectures, keeping data consistent and synchronized across microservices, regions, and data centers becomes a complex challenge. Whether you’re replicating databases, syncing caches, or coordinating global services — you need a fast, fault-tolerant, and scalable messaging system.

Apache Pulsar provides the perfect foundation for data synchronization in distributed systems. Its architecture, built around multi-tenancy, geo-replication, and decoupled storage/compute, offers robust mechanisms for keeping services in sync in real time.

Why Use Pulsar for Data Synchronization?

Key capabilities of Pulsar that make it ideal:

  • Native geo-replication for syncing data across regions
  • Flexible subscription models for event replays and state convergence
  • Guaranteed message delivery with configurable acknowledgments
  • Built-in message ordering with Key_Shared subscriptions
  • High throughput and low latency

Whether synchronizing across cloud regions or microservices, Pulsar ensures that eventual consistency or real-time convergence is achievable.

Common Use Cases

  • Multi-region database replication
  • Event-based cache invalidation
  • Microservice state synchronization
  • User profile propagation
  • IoT device state coordination
  • Log shipping across clusters

Pulsar Architecture for Synchronization

[Service A (US-East)]               [Service B (EU-Central)]
↓                                    ↓
[Topic: profile-events] ← Geo-Replicated → [Topic: profile-events]
↓                                    ↓
[Consumers: Update DB, Cache]      [Consumers: Update DB, Cache]
  • Pulsar’s multi-cluster replication ensures messages published in one region are propagated globally
  • Use shared or key-shared subscriptions for concurrent processing
  • Use cumulative acknowledgments for efficient commit tracking

Setting Up Geo-Replication

Step 1: Configure brokers in each region to form a multi-cluster setup.

Step 2: Enable replication at the namespace level:

bin/pulsar-admin namespaces set-clusters \
--clusters us-east,eu-central \
my-tenant/my-namespace

Step 3: Write messages in one region, and Pulsar automatically replicates to others.

Achieving Order and Consistency

For ordered synchronization (e.g., updates to the same user), use Key_Shared subscriptions:

Consumer<byte[]> consumer = client.newConsumer()
.topic("profile-updates")
.subscriptionName("profile-sync")
.subscriptionType(SubscriptionType.Key_Shared)
.subscribe();

This ensures all events for a given key (like user_id) are routed to the same consumer, preserving event order.

Exactly-Once and Idempotency

Pulsar supports effectively-once delivery semantics via message deduplication and idempotent processing:

  • Use message IDs or custom UUIDs to deduplicate
  • Track last processed event IDs in your services
  • Avoid side effects in message handlers unless the operation is committed

Synchronization Patterns

1. Event Sourcing

Store state changes as a series of Pulsar events:

  • Producers emit changes (user.updated, order.shipped)
  • Consumers reconstruct state or apply deltas
2. Command Query Responsibility Segregation (CQRS)
  • Commands modify data and produce events
  • Events are consumed by read models (e.g., Redis, Elasticsearch) and replicated services
3. Dual-Writing Prevention

Avoid writing directly to databases and publishing separately. Instead:

  • Use a Pulsar Function or message router to publish and persist atomically

Monitoring and Delivery Guarantees

  • Use ack timeouts and dead-letter topics to avoid message loss
  • Monitor with Prometheus, Grafana, and built-in Pulsar metrics:
    • pulsar_replication_backlog
    • pulsar_out_rate
    • pulsar_subscription_lag

Security and Compliance

  • Use TLS and JWT to authenticate publishers/consumers across regions
  • Apply role-based access control per namespace or topic
  • Enable audit logging for message access and data integrity

Best Practices

  • Use compact topics for the latest state views (e.g., device-status)
  • Leverage retry topics for transient sync failures
  • Use Pulsar IO or Functions for filtering, transformation, and routing
  • Deploy brokers and bookies closer to the data source for lower latency

Conclusion

Apache Pulsar provides a reliable, scalable, and feature-rich platform for synchronizing data across distributed systems. With support for geo-replication, subscription flexibility, and built-in fault tolerance, Pulsar simplifies the challenges of keeping services consistent in a globally distributed world.

From database replication to microservice event propagation, Pulsar ensures your systems are always in sync, responsive, and ready for scale.