Introducing CrossFireSync

On April 16, 2024, UnitVectorY Labs launched CrossFireSync, a new open-source Java library that enables real-time synchronization of Google Cloud Firestore databases across different geographic regions. This capability fills a critical gap for organizations running globally distributed applications that need low-latency access to data while maintaining regional compliance requirements.

Firestore doesn’t natively support cross-region database replication. CrossFireSync solves this problem by leveraging Google Cloud Pub/Sub to bridge the gap between regional Firestore instances, giving developers fine-grained control over their multi-region data architecture.

What’s New

CrossFireSync v0.0.1 introduces two operational modes to suit different application needs:

Single Region Primary Mode

Ideal for applications where all writes naturally flow through a central region. In this mode:

  • All write operations target a single primary region
  • Changes automatically replicate to other configured regions
  • Documents remain clean with no additional attributes

This approach provides the simplest data model while still delivering read latency benefits from regional replicas.

Multi Region Primary Mode

For applications that need write availability from any geographic location:

  • Writes can be directed to any region
  • Each region deploys both publisher and consumer functions
  • Enables true distributed write capabilities

This mode adds replication tracking attributes (crossfiresync:timestamp, crossfiresync:sourcedatabase, crossfiresync:delete) to documents, giving you flexibility at the cost of a slightly more complex schema.

Production-Ready Foundation

The initial release includes:

  • Two Cloud Functions working together for bidirectional replication
  • Comprehensive test coverage ensuring reliable operation
  • Maven Central distribution for easy integration (com.unitvectory:crossfiresync:0.0.1)
  • Apache 2.0 licensing for commercial and personal use

Why It Matters

Solving a Real GCP Gap

Google Cloud Firestore doesn’t provide built-in cross-region replication. Teams needing this capability previously had to build custom solutions from scratch. CrossFireSync delivers a battle-tested implementation that handles the complexity of Pub/Sub messaging, document change detection, and conflict resolution.

Flexible Deployment Strategies

Not every application has the same requirements. CrossFireSync’s dual-mode approach lets teams choose their consistency model:

  • Latency-focused apps can use single-region primary to serve reads from nearby regions while keeping writes centralized
  • Globally distributed apps can use multi-region primary to accept writes from any location, improving availability for users worldwide

Built for Java Developers

As a native Java library with first-class Cloud Functions support, CrossFireSync integrates seamlessly into existing GCP + Java ecosystems. The clean API and factory pattern design make it straightforward to configure and extend.

Getting Started

CrossFireSync is available on Maven Central. Add it to your pom.xml:

<dependency>
    <groupId>com.unitvectory</groupId>
    <artifactId>crossfiresync</artifactId>
    <version>0.0.1</version>
</dependency>

Prerequisites

  • Java 17 or higher
  • GCP project with Firestore and Pub/Sub enabled
  • Cloud Functions deployment access

Deployment Overview

The library ships with two Cloud Functions:

  • FirestoreChangePublisher: Listens to Firestore changes and publishes to Pub/Sub
  • PubSubChangeConsumer: Consumes Pub/Sub messages and updates local Firestore

Deploy these functions according to your chosen replication mode, configuring environment variables for REPLICATION_MODE and DATABASE_NAME.

Important Considerations

CrossFireSync provides eventual consistency across regions. Due to the nature of distributed systems:

  • Conflicting edits in separate regions may result in last-write-wins behavior
  • Best practice is to route writes for individual documents to the same region when possible
  • No global transactions span multiple regions

Review the full documentation before deploying to production.

Transparency Note

This post was AI-generated using the unsloth/Qwen3.5-122B-A10B-GGUF:Q4_K_M model. It was generated on March 18, 2026, based on the v0.0.1 release of the crossfiresync repository. The author is release-storyteller.