Building dApps with Custom ZK Rollups: Polygon CDK + Avail

In the rapidly evolving world of blockchain technology, scalability remains a pivotal challenge. Within the ecosystem, Zero-Knowledge Rollups (ZK Rollups) technology is a promising solution that can enhance the efficiency and scalability of decentralized applications (dApps) development. This guide walks you through the essentials of building custom ZK Rollups using Polygon CDK and Avail, providing insights into their benefits, integration, and real-world applications.

Introduction to Polygon CDK (Chain Development Kit)

Polygon CDK (Chain Development Kit) is an open-source toolkit for launching your own Layer 2 (L2) ZK-powered chain on Ethereum. Instead of deploying a monolithic smart contract, you get a modular stack (sequencer, bridge, RPC node) that you can configure. So it is basically creating your own zkEVM chain without building everything from scratch.

What is Avail?

Avail solves a critical problem of data availability. It is a modular Data Availability (DA) layer. Instead of posting transaction data to Ethereum, your rollup posts it to Avail, which guarantees data is available using Data Availability Sampling (DAS). Posting calldata to Ethereum costs roughly 16 gas/byte. Avail's DA sampling brings this to near-zero, making your rollup orders of magnitude cheaper for users.

Why Combine Polygon CDK + Avail?

By default, many rollups use Ethereum for data availability which is expensive. Using Avail we can get cheaper Data Availability Later, Better scalability and Modular Architecture.

Here's how the system works step-by-step:

• Users submit transactions to your rollup
• Polygon CDK executes transactions off-chain
• A ZK proof is generated
• Transaction data is sent to Avail
• Proof is submitted to Ethereum.
• Ethereum verifies the proof.

Also, Read | Building a Cross-Chain

 Decentralized Application with LayerZero

Step-by-Step Setup :

Environment Setup :

# Node.js (>=18)
node -v

# Docker
docker -v

# Git
git --version

Clone CDK:
git clone https://github.com/0xPolygon/cdk-validium-stack.git
cd cdk-validium-stack

Configure Rollup:

Define your chain-level configs:

• Chain ID
• Gas token
• Block time
• Sequencer address

 YAML

chain:
  id: 12345
  name: 'MyZKRollup'

sequencer:
  address: '0xYourSequencerWallet'

gas:
  token: 'ETH'

Integrate Avail:

Run Avail node OR use hosted endpoint,
Configure DA client in CDK

 env

DA_LAYER=avail
AVAIL_RPC=https://avail-rpc-endpoint
AVAIL_SEED_PHRASE='your mnemonic'

Start Core Services:

docker-compose up

This Starts up:
 

• Sequencer
• RPC node
• Prover
• Database

Deploy Smart Contracts (Ethereum)

npx hardhat run scripts/deploy.js --network goerli

Set up Bridge:

Bridge allows:
L1 → L2 deposits
L2 → L1 withdrawals

Key configs:
Token mapping
Message passing

Once everything is running:

RPC available at:
http://localhost:8545

Add network to Metamask and Start sending transactions.

Also, Discover | Zero-Knowledge Proof for Blockchain Transaction Privacy 

Key Concepts Summary

Users send txs → Sequencer batches them → posts tx data to Avail → ZK Prover generates validity proof → Aggregator submits proof to Ethereum L1 verifier contract → state root updated on L1.

Conclusion

Custom ZK rollups represent the next evolution of scalable blockchain infrastructure, enabling developers to build high-performance dApps without sacrificing Ethereum's security guarantees. By combining Polygon CDK's modular zkEVM framework with Avail's efficient data availability layer, teams can significantly reduce transaction costs, improve throughput, and maintain decentralized verification.

For builders looking to future-proof their blockchain architecture, integrating custom ZK rollups with Polygon CDK and Avail is not just an optimization "” it's a strategic step toward the next generation of Web3 infrastructure. Connect with our skilled blockchain developers for a quick consultation for your blockchain project.