How to Plan a Rollup Architecture

Rollups are Layer 2 scaling solutions that execute transactions off-chain and post compressed data to a base Layer 1 (L1) like Ethereum for security. The primary architectural decision is choosing between a ZK-Rollup and an Optimistic Rollup. ZK-Rollups use cryptographic validity proofs (e.g., zk-SNARKs, zk-STARKs) to instantly verify state correctness, offering fast finality and strong security. Optimistic Rollups assume transactions are valid but include a fraud-proof window (typically 7 days) where anyone can challenge invalid state transitions, prioritizing EVM compatibility and developer familiarity.

Your data availability (DA) strategy is critical for security and cost. The default is to post all transaction data as calldata on Ethereum L1, ensuring maximum security but at higher cost. Alternatives include using Ethereum's EIP-4844 blobs for cheaper temporary storage or a separate Data Availability Committee (DAC) or validium for off-chain data, which reduces fees but introduces trust assumptions. The choice directly impacts your rollup's security model, decentralization, and transaction cost for end-users.

The sequencer is the node responsible for ordering transactions and producing blocks. A single, centralized sequencer offers simplicity and low latency but creates a censorship risk and single point of failure. Decentralizing the sequencer set, often through a proof-of-stake mechanism, enhances censorship resistance and liveness but adds implementation complexity. You must also decide on transaction finality—whether users wait for L1 confirmation (hard finality) or accept faster, soft confirmations from the sequencer.

Smart contract architecture on the rollup involves deploying a core set of contracts on the L1 and L2. On L1, you need a bridge contract for deposits/withdrawals and, for Optimistic Rollups, a fraud verifier. On L2, you deploy the execution environment (e.g., an EVM-compatible node client like geth modified for rollup operation). For ZK-Rollups, you must also integrate a prover system to generate validity proofs for each batch, which requires selecting a proving scheme and managing prover hardware.

Interoperability and the user/developer experience are key to adoption. Plan for a canonical bridge to your base L1 and consider integrations with cross-chain messaging protocols like LayerZero or Axelar for broader connectivity. The developer experience hinges on your virtual machine choice: maintaining full EVM equivalence (as with Optimism or Arbitrum) offers the easiest migration, while a custom VM (like Starknet's Cairo) can offer performance benefits but requires new tooling. Provide robust RPC endpoints, block explorers, and SDKs.

Finally, establish a roadmap for decentralization and governance. Start with a controlled, secure launch using a permissioned sequencer and clear upgrade mechanisms (often via a multisig). Plan progressive milestones to decentralize sequencer selection, move towards permissionless proving, and eventually transition upgrade control to a token-based governance system. Documenting this transparent plan builds trust with your user base and aligns with the core ethos of blockchain technology.

Planning a rollup architecture begins with a clear definition of your goals. Are you optimizing for maximum throughput, minimal transaction costs, or a specific developer experience? Your primary objectives will dictate your choices for the execution environment—whether you need a general-purpose EVM-compatible chain (like an Optimism or Arbitrum L2), a custom zkEVM (such as those from Polygon zkEVM or Scroll), or a high-performance application-specific rollup using a framework like Sovereign. This decision impacts your developer tooling, smart contract compatibility, and the complexity of your proving system.

The data availability (DA) layer is your next critical decision. It determines where transaction data is published and verified. Using Ethereum as a DA layer (via calldata or blobs) provides the highest security but at a cost. Alternatives include EigenDA, Celestia, or Avail, which offer lower costs and higher throughput but introduce a different trust model. Your choice here directly affects your rollup's security budget, finality time, and compatibility with the broader ecosystem. For example, a rollup using Ethereum for DA can leverage native bridging via canonical bridges, while an external DA solution requires a separate bridge or light client verification.

You must then design your sequencer and prover infrastructure. A centralized sequencer offers simplicity for launch but becomes a single point of failure and censorship. Decentralizing the sequencer set, as explored by protocols like Espresso or Astria, enhances resilience. For ZK-Rollups, you need to plan your proving system: will you use a CPU-based prover for flexibility or specialized hardware (GPU/FPGA/ASIC) for performance? This involves selecting a proof system (e.g., Plonky2, Halo2, STARKs) and planning for proof aggregation and recursion to manage costs.

Finally, map out your bridge and withdrawal mechanisms. Users need a secure way to deposit assets from L1 and withdraw them back. This involves deploying a set of bridge contracts on the L1 and your rollup. For Optimistic Rollups, you must define the challenge period (typically 7 days) and the fraud proof system. For ZK-Rollups, you need to establish the verifier contract on L1 and the frequency of validity proof submission. Thoroughly test these components, as bridge vulnerabilities are a primary attack vector. Use established libraries like the OP Stack's bridge contracts or the zkSync Era bridge as reference implementations.

Planning a rollup architecture begins with defining its core purpose and trade-offs. You must choose between a ZK-Rollup for cryptographic security and fast finality, or an Optimistic Rollup for EVM compatibility and lower development complexity. This foundational decision impacts your data availability strategy—whether transaction data is posted to Ethereum Mainnet (ensuring maximum security) or to an external data availability layer like Celestia or EigenDA (reducing costs). Your chosen sequencer model, whether a single trusted operator or a decentralized network, dictates censorship resistance and liveness guarantees.

The execution environment is your rollup's virtual machine. For general-purpose smart contracts, the Ethereum Virtual Machine (EVM) is the standard, enabling seamless porting of dApps via forks like Arbitrum Nitro or Optimism's OVM. For specialized applications requiring high throughput, consider a custom VM like the zkEVM (e.g., Polygon zkEVM, zkSync Era) or a non-EVM environment like Solana's SVM as used by Eclipse. Your VM choice determines developer tooling, language support (Solidity, Vyper, Rust), and the complexity of proving systems for ZK-Rollups.

A critical technical component is the state management system. You must design how the rollup's state root is computed, updated, and verified. For Optimistic Rollups, this involves a fraud-proof window (typically 7 days) where anyone can challenge invalid state transitions. For ZK-Rollups, a validity proof (ZK-SNARK or STARK) must be generated for each batch and verified on L1. The prover system, whether centralized or decentralized, becomes a major performance bottleneck; optimizing proof generation time and cost is essential for user experience.

Finally, plan the bridge and messaging layer for asset and data transfer between L1 and L2. This includes the canonical bridge contract on Ethereum that locks assets and a corresponding mint/burn mechanism on the rollup. For cross-rollup communication, you'll need to implement a standard like the Arbitrary Message Passing (AMP) protocol. Security here is paramount; a bug in the bridge contract is a single point of failure that can lead to total fund loss, as seen in historical exploits. Thorough audits and gradual, permissioned upgrades are mandatory.

A rollup's data availability layer is the system that stores and guarantees access to transaction data. This is distinct from execution; it's about ensuring anyone can reconstruct the rollup's state to verify its correctness. The primary options are on-chain Ethereum (calldata or blobs), off-chain solutions like Celestia or Avail, and hybrid approaches. Your choice directly impacts security assumptions, transaction costs, and the trust model for users and validators.

Using Ethereum for DA, via EIP-4844 blob transactions, provides the highest security by inheriting Ethereum's consensus. This is the standard for optimistic rollups like Arbitrum and zk-rollups like zkSync. Blobs are cheaper than calldata but are pruned after ~18 days, requiring long-term archival solutions. The cost is variable and denominated in ETH, making it suitable for applications prioritizing maximal security over absolute lowest cost.

Off-chain DA layers like Celestia or EigenDA offer significantly lower costs by using a separate, specialized network for data publishing. This introduces a new trust assumption: the security of the rollup is now tied to the DA layer's own validator set. These are ideal for high-throughput appchains or rollups where cost minimization is critical and the DA layer's security is deemed sufficient. Integration requires using the layer's SDK, such as the @rollkit framework for Celestia.

A validium architecture, used by StarkEx, stores data off-chain (e.g., on a committee or DAC) while posting validity proofs to Ethereum. This offers Ethereum-level security for execution correctness but not for data availability. A volition, like those offered by StarkWare, lets users choose per-transaction between a full zk-rollup (data on Ethereum) and a validium mode, providing flexibility between cost and security.

When planning, model your cost structure using projected transaction volume and current blob/DA pricing. Evaluate your security requirements: financial applications may need Ethereum DA, while a gaming rollup might opt for a cost-effective off-chain layer. Finally, assess ecosystem fit—choosing a popular DA layer like Celestia can improve interoperability with other rollups in its ecosystem through shared liquidity and tooling.

Your architecture should document the DA choice clearly. For example, a config file might specify data_availability_layer: "celestia" and da_namespace: "ABC123". Always implement a robust data availability challenge or proof verification mechanism appropriate to your stack, ensuring users have recourse if data is withheld, which is the core failure mode all DA solutions must mitigate.

Planning a rollup architecture begins with defining the roles of the sequencer and prover. The sequencer is the primary execution node responsible for ordering transactions, executing them against the rollup's state, and batching them into blocks. The prover, often a separate system, generates cryptographic proofs (like ZK-SNARKs or ZK-STARKs) that attest to the correctness of the state transitions within those blocks. Your first decision is whether to adopt a centralized sequencer for initial simplicity or design for decentralized sequencing from the start, which impacts liveness guarantees and censorship resistance.

The choice between a ZK-Rollup and an Optimistic Rollup fundamentally shapes your prover architecture. For a ZK-Rollup, you must integrate a proving system (e.g., zkEVM circuits using Halo2, Plonky2, or RISC Zero) and plan for the computational overhead of proof generation. This involves selecting a proof system based on trust assumptions, proof size, and verification cost on L1. For an Optimistic Rollup, the "prover" role shifts to a network of verifiers who challenge invalid state roots during the dispute period, requiring a fraud-proof system like Cannon or a custom fraud-proof VM.

You must architect the data flow between components. The sequencer publishes calldata or blobs to an L1 data availability layer (like Ethereum or Celestia) and submits state commitments. The prover consumes this data to generate validity proofs or fraud proofs. This pipeline must handle failures gracefully; for instance, if the prover fails, you may need a fallback mechanism or a proof marketplace to ensure liveness. Tools like the OP Stack or ZK Stack provide modular blueprints, but you'll need to configure them for your specific VM and proving needs.

Performance planning is critical. Benchmark your sequencer's transactions per second (TPS) under load and model proof generation times, which can range from seconds to minutes depending on block size and hardware. For ZK-Rollups, consider using specialized hardware (GPU/FPGA provers) or cloud services (AWS Nitro Enclaves) to accelerate proving. The architecture must also account for economic incentives: sequencers may earn fees, while provers require compensation for their computational work, often via a proof auction or a staking mechanism.

Finally, plan for upgrades and security. Use proxy contracts for your core rollup contracts on L1 to enable future improvements. Implement multi-signature controls or a timelock for administrative actions. Your architecture should include monitoring for sequencer health, proof generation latency, and data availability posting success. By explicitly defining the interfaces, failure modes, and incentives between your sequencer and prover, you build a foundation for a robust, scalable Layer 2.

Planning a rollup architecture begins with selecting the execution environment, which defines how transactions are processed and state is computed. The two primary models are ZK-Rollups and Optimistic Rollups. ZK-Rollups (e.g., zkSync Era, Starknet) use cryptographic validity proofs to verify state transitions off-chain, offering near-instant finality. Optimistic Rollups (e.g., Arbitrum, Optimism) assume transactions are valid and use a fraud-proof challenge period, prioritizing EVM compatibility and lower computational overhead. Your choice dictates security assumptions, finality speed, and development complexity.

The core of the execution environment is the Virtual Machine (VM). The dominant choice is the Ethereum Virtual Machine (EVM), enabling seamless compatibility with Ethereum tooling, wallets, and existing smart contracts. Alternatives include custom VMs like StarkWare's Cairo VM for ZK-provable computation or the Fuel VM for parallel transaction processing. Selecting a non-EVM chain requires building a new developer ecosystem but can unlock optimizations like native account abstraction or more efficient proof generation. Consider your target developer audience and required performance characteristics.

You must architect the sequencer, the node responsible for ordering transactions. A centralized sequencer offers simplicity and high performance but introduces a single point of failure and censorship risk. Decentralizing the sequencer set, as seen with Espresso Systems or Astria, enhances censorship resistance but adds consensus complexity. The sequencer batches transactions and posts compressed data to the base layer (Data Availability layer). This data is either published as calldata on Ethereum or to a specialized Data Availability (DA) layer like Celestia or EigenDA, a major cost and scalability determinant.

The proving system is critical for ZK-Rollups. You must choose a proof system (e.g., SNARKs, STARKs) and a proof scheme (e.g., Groth16, Plonk, STARK). SNARKs have smaller proof sizes but require a trusted setup; STARKs are trustless but generate larger proofs. You'll need to integrate a prover service to generate these proofs and a verifier smart contract on the base layer to check them. This stack choice affects proof generation time, verification cost, and the ability to support complex, general-purpose smart contracts.

Finally, define the bridge and messaging layer for asset and data transfer between the rollup and external chains. This includes the canonical bridge to the base L1 for deposits/withdrawals and potentially a cross-chain messaging protocol (like LayerZero or Hyperlane) for broader interoperability. Security here is paramount; the bridge's trust model should align with the rollup's overall security. A well-planned architecture balances performance, cost, security, and developer experience to create a sustainable and scalable L2 solution.

Before writing a line of code, define your rollup's core architectural pillars. The first decision is the data availability (DA) layer. Using Ethereum for DA (like Optimism and Arbitrum) provides maximum security but incurs higher costs. Alternatives include EigenDA, Celestia, or a dedicated DA blockchain, which offer lower fees but introduce trust assumptions. Your choice here dictates your security model, cost structure, and interoperability potential. Simultaneously, select your virtual machine (VM). The EVM is the standard, ensuring compatibility with existing tooling and developers. For novel use cases, consider a custom VM (like FuelVM or SVM) or a zkVM (like RISC Zero) for specific performance or proving advantages.

Next, design your sequencer and prover infrastructure. Will you run a single, permissioned sequencer for simplicity, or plan for a decentralized network? For ZK-Rollups, you must architect the prover system: decide between a centralized prover, a decentralized prover network (e.g., using Espresso Systems for sequencing), or an outsourced service. This component is critical for liveness and censorship resistance. You also need to plan the bridge and messaging layer. The canonical bridge to L1 must be securely implemented for asset deposits and withdrawals. For cross-rollup communication, evaluate standards like LayerZero, Wormhole, or the native IBC protocol if building on Cosmos.

The final planning phase involves node software and tooling. You will need to implement or fork a full node client (e.g., based on op-geth or Arbitrum Nitro) that includes an execution engine, a rollup-specific consensus layer, and a synchronization module. Plan your data indexing strategy—will you support a subgraph on The Graph or run an internal indexer? Developer experience is crucial; ensure compatibility with standard wallets (MetaMask), block explorers, and RPC services. Establish a plan for governance and upgrades, determining how protocol changes will be proposed and executed, often managed through a multisig or DAO in the initial stages.

Thorough planning in these areas—DA layer, VM, sequencer design, bridging, and node infrastructure—creates a coherent blueprint. This upfront work prevents costly refactoring later and clearly defines the security, performance, and decentralization trade-offs of your rollup. The next step is to move from this architectural checklist to the implementation phase, building and testing each component against your specifications.