🏗️ Bridge Architecture: Validators & Relayers
Learn the components that power cross-chain communication
Transfer assets between different blockchains
Your Progress
0 / 5 completed🏗️ Production Bridge Architecture
Understanding bridge architecture at the implementation level is critical for developers building or integrating cross-chain apps. A production bridge involves 7 distinct steps spanning multiple actors (user, smart contracts, relayers, validators) and both chains. Ethereum → Polygon transfer takes ~10-30 minutes from user initiation to final receipt. Each step has specific gas costs, time estimates, and failure modes. Relayers provide liveness (message passing) while validators provide security (signature verification). Gas optimization is crucial—Polygon Bridge batches proofs to reduce L1 costs. This section breaks down the complete flow with real code examples from production bridges.
🎮 Interactive: 7-Step Transaction Flow
Click through each step of a real bridge transaction. See the actors involved, time estimates, gas costs, technical details, and actual code snippets.
User Initiates Bridge
User connects wallet, selects source/dest chains, amount, clicks "Bridge"
- •Frontend calls: bridgeContract.lock(amount, destChain, destAddress)
- •User approves token spend if ERC20 (not needed for native ETH)
- •Transaction broadcast to source chain mempool
// Frontend code
const tx = await bridgeContract.lock(
ethers.utils.parseEther("10"), // amount
137, // Polygon chain ID
userAddress // destination address
)👥 Key Actors in Bridge Architecture
🔄 Relayers
Off-chain services that watch both chains and relay messages. Provide liveness.
- • Run full nodes on source + destination chains
- • Monitor for LockEvents, submit proofs to destination
- • Anyone can run a relayer (permissionless)
- • Incentivized via fees (~0.1% of bridge volume)
- • Cannot forge messages (no validator keys)
✓ Validators
Consensus participants who sign cross-chain messages. Provide security.
- • Hold private keys, sign messages after independent verification
- • Typically staked (Polygon: 1M MATIC minimum)
- • Slashable if sign invalid messages
- • N-of-M threshold (e.g., 2/3 must agree)
- • Decentralization critical (Ronin had only 9 validators)
⚡ Gas Optimization Strategies
1. Batch Processing
Instead of relaying each lock event individually (expensive L1 gas), batch multiple events into single Merkle tree. Submit root + proofs. Polygon processes 100+ checkpoints per Ethereum transaction.
2. ZK Proof Aggregation
zkSync, StarkNet compress 1000s of transactions into single proof (~200 bytes). Verification cost constant regardless of transaction count. Future of bridges.
3. State Compression
Store only Merkle roots on L1, full state on L2/off-chain. User provides inclusion proof when withdrawing. Reduces L1 storage costs 10-100x.
4. Optimistic Assumptions
Assume messages valid, only verify if challenged (Optimism model). Fast deposits (1 confirmation), slow withdrawals (7-day challenge). Most transfers honest = cheaper on average.