CCNext Cross-Chain Bridge Worker

🔭 Overview

A production-grade off-chain worker system that orchestrates cross-chain token transfers between Ethereum Sepolia and a custom Substrate-based L2 (CCNext). This is the infrastructure layer that makes the bridge actually work — event monitoring, proof generation, confirmation handling, and cross-chain submission, all with proper resilience patterns.

❓ The Problem

Cross-chain bridges require an off-chain coordinator: something that watches for events on the source chain, waits for sufficient confirmations, requests a cryptographic proof from an external prover service, then submits that proof to the destination chain. Every step can fail, and failures need to be handled gracefully without double-spending or losing transactions.

🛠️ Architecture

Ethereum Sepolia (ERC-20 Transfer Event)
    ↓ wait N confirmations
Off-Chain Worker (NestJS)
    ↓ call Proof API (exponential backoff, 20 retries, 15-min timeout)
External Proof API (generates cryptographic inclusion proof)
    ↓ submit proof transaction
CCNext L2 (USC Contract — verify proof + mint)

🛠️ What I Built

📡 Event Monitoring Layer

📡 Subscribes to Ethereum Sepolia ERC-20 Transfer events via ethers.js
⏳ Implements confirmation window logic: waits for N block confirmations before processing
💾 Persistent event state tracking in PostgreSQL via TypeORM (prevents reprocessing on restart)

🔄 Proof API Orchestration

🔁 Calls external Proof API with exponential backoff retry (20 attempts, 15-minute total timeout)
🛡️ Handles API timeouts, rate limits, and transient failures gracefully
📋 Logs all retry attempts with structured metadata for observability

📤 CCNext Transaction Submission (viem)

⛓️ Uses viem for CCNext L2 interactions (EIP-1559 transaction construction)
🔢 Per-wallet nonce management: tracks nonce per wallet address to enable parallel transaction submission
👛 Supports 4 concurrent wallets with independent nonce tracking

🧪 Traffic Simulator

🔧 Companion tool that generates parallel ERC-20 transfers across 4 wallets for load testing
🔢 Per-wallet nonce management with EIP-1559 support
✅ Used for end-to-end bridge flow validation and stress testing

⚙️ Infrastructure

🐳 Docker Compose with NestJS worker + PostgreSQL + Redis
☁️ Azure App Configuration for dynamic config management across environments
🌐 Environment-specific deployments: testnet, devnet, production

⭐ Key Highlights

🔁 Exponential backoff proof API retry: 20 attempts, 15-min total timeout — handles real network conditions
🔢 Per-wallet nonce management enabling parallel cross-chain submissions
💾 Persistent state prevents duplicate processing on worker restart
☁️ Full multi-environment support via Azure App Configuration
🧪 Companion traffic simulator for end-to-end load testing

🔗 CCNext Cross-Chain Bridge Worker

Stack