Rollup-as-a-Service Challenges and Opportunities: From Multi-Chain to Multi-Rollup

Cosmos and Polkadot adopt the expansion scheme of multi-chain structure. Their blockchain SDKs, Tendermint and Substrate, are used by many projects to customize their own blockchains. These blockchains use cross-chain protocols such as Cosmos IBC[1], Polkadot XCM[2] and bridges[3] to interact. However, it is difficult for these protocols to guarantee high security, which leads to frequent hacking. Therefore, the cross-chain protocol did not bring the expected effect, and the blockchains remained relatively independent.

Rollup-as-a-Service Challenges and Opportunities: From Multi-Chain to Multi-Rollup

From Cosmos Network – Internet of Blockchains[4] and Getting Started · Polkadot Wiki[5]

Later, a more secure scaling technique called rollup emerged. A rollup compresses layer 2 transactions into a “batch”, uploads it to layer 1, and proves the validity of layer 1 state transitions through fraud proofs (like Optimistic-rollup) or validity proofs (like ZK-rollup) sex. Since the availability of data and the validity of the state are verified at Tier 1, rollup achieves the same level of security as Tier 1, ensuring that assets can be safely transferred between Tier 1 and Tier 2.

Many rollup projects such as Arbitrum, Optimism, ZkSync and StarkNet are already in use so far. In addition to these general rollups, some application-specific rollups have also appeared, including dYdX (order book DEX) and DeversiFi (AMM DEX) based on the StarkEx rollup SDK[6]. Although rollup technology is not yet fully developed, and there are not many teams that master it, the market demand for this technology is still strong.

Rollup-as-a-Service Challenges and Opportunities: From Multi-Chain to Multi-Rollup

General-purpose and application-specific rollups from

rollup provides a self-contained execution environment with high TPS, low gas and the ability to access all assets from layer 1, which helps applications on the blockchain expand from DeFi to more general areas such as gaming and social networking . We expect rollup will gradually become a service provided to Web3 applications, namely Rollup as a Service (Raas). Some projects are now moving in this direction. Ethereum’s rollup-centric roadmap [8] and StarkNet’s Layer 3 [9] architecture both demonstrate a multi-rollup future for specific applications.

Rollup-as-a-Service Challenges and Opportunities: From Multi-Chain to Multi-Rollup

Architecture description of StarkNet, using multiple rollup of specific applications as Layer 3, source Medium [10]

Challenges of building RaaS

Rollup still faces the following challenges in delivering RaaS.


First, let’s talk about the rollup SDK. One can quickly deploy some configuration and start a rollup on top of the SDK. To avoid reinventing the wheel, an open source rollup is a better choice for SDK development. For Optimistic-rollup, both Arbitrum and Optimism are open source. From L2beat, we can see that both Metis and Boba are developed on the basis of Optimism’s code. In contrast, ZK-rollup is not very open source. ZkSync released the full code for v1 [11], but only the contract code [12] for v2 (with zkEVM embedded). StarkEx only releases the contract code [13] and provides other modules to third parties through a closed source code. StartNet only provides Cairo’s code [14].

Although Optimistic-rollup systems have more mature codebases and better support for EVM, the inherent properties of fraud proofs make them far behind ZK-rollup systems in terms of finality and security. ZK-rollup layer 2 transactions complete as soon as layer 1 is proven, while Optimistic-rollup layer 2 transactions take days to complete due to a challenge period. On the other hand, Optimistic-rollup requires more security assumptions: at least 1-out-of-N honest operators to guarantee fraud proof submission, and a censorship-resistant layer 1 to guarantee fraud proof acceptance.

All in all, we can quickly build an Optimistic-rollup SDK on top of existing open source code right now, but the ZK-rollup SDK seems more attractive in the long run. Of course, in addition to codebase issues, the design of ZKVM, ie ZKP verifiable smart contracts, is also urgently needed. Currently, various ZKVM solutions are under development. The approach to each solution is still not uniform.

Rollup-as-a-Service Challenges and Opportunities: From Multi-Chain to Multi-Rollup

A picture to compare ZKVM, source: Ye Zhang’s talk “An overview of zkEVM[15]”


As mentioned earlier, batched transactions need to be sent to layer 1 in a rollup manner, so the TPS of rollup is limited by the storage space of layer 1, which is the data availability [16] (DA) problem. Ethereum has proposed a series of layer 1 storage scaling solutions, including EIP-4488, Proto-Danksharding, and full Danksharding (proposals are currently being sought [17]). In addition to the expansion of tier 1, many projects such as Celestia and Polygon Avail are also trying to expand the storage capacity of tier 2. However, the security and ease of use of these solutions still requires further research.

Rollup-as-a-Service Challenges and Opportunities: From Multi-Chain to Multi-Rollup

How EIP-4488 and Proto-danksharding will increase block size, source: Vitalik’s “Proto-Danksharding FAQ[18]”

In terms of ZK-rollup, TPS is also limited by the speed of ZKP computation. Paradigm and 6block have different hardware options on GPU, FPGA and ASIC to accelerate computation. Additionally, 6block compares several ZKP distributed computing software architectures, including mining pools, proof aggregation, and DIZK. ZPrize[19], an upcoming competition, also motivates developers to find valuable solutions to speed up ZKP computations.

Ensuring high availability of the rollup service is another key issue. The rollup services on the market today are almost all centralized, that is, only specific operators can submit batches and proofs to layer 1. This is a fragile design as SPOF (single point of failure) will easily render the service unavailable. Arbitrum has suffered several hours of downtime due to software bugs [20] and hardware failures [21]. Many projects are working on decentralizing rollup to avoid SPOF, including zkSync [22], StarkNet [23], Polygon Hermes [24], PoVP [25], and [26].

economic model

RaaS is considering applying a good economic model. Currently, the profit of service providers mainly comes from the transaction fee gap between tier 1 and 2, that is, collecting fees from tier 2 as revenue and paying fees to tier 1 as costs. Optimism has issued governance tokens [27], but the revenue is still not enough to sustain expenses.

Rollup-as-a-Service Challenges and Opportunities: From Multi-Chain to Multi-Rollup

rollups and their fees, from

Most existing rollups are third-party services built on the blockchain, so their main revenue comes only from transaction fees. However, we can think outside of this mindset and think of rollup as a native service provided by the blockchain. Just like the design of Cosmos and Polkadot, the entire system consists of a blockchain and multiple rollups attached to the blockchain, forming a decentralized network with infinite scalability. In this way, the network can reward layer 1 blockchain validators and layer 2 rollup operators with the same native token. This idea is similar to the shrined rollup proposed by Polynya [29] and deserves further study.

Functional aspects

Like the cross-chain protocols of Cosmos and Polkadot, the cross-rollup protocol is necessary when multiple rollups are deployed on a blockchain. Users can also withdraw their assets from Tier 1 and deposit them in another rollup, but this process requires additional fees and more steps in Tier 1. Some third-party cross-rollup bridges [30] utilize liquidity pools to help users transfer instantly between rollups, but these bridges are just as easy to steal as cross-chain bridges.

Rollup-as-a-Service Challenges and Opportunities: From Multi-Chain to Multi-Rollup

A future blockchain architecture described by Vitalik in Endgame [31] with multiple rollup and cross-rollup bridges

Ideally, the blockchain should provide a native cross-rollup bridge maintained by its validators for security. Also, such a bridge would ideally support synchronous message calls from one rollup to another, that is, a user on one rollup could directly call a contract on another rollup. This will maximize the user experience in a multi-rollup architecture. The underlying technology here is complex, but we look forward to it.


This article describes RaaS, a rollup service for DApps. Clearly, the blockchain will usher in the multi-rollup future of Web3. Anyone can quickly launch their rollup through the SDK and run applications on the rollup with high performance and low cost. After discussing all the challenges that RaaS might face, we finally came up with the idea of ​​native rollups, which would help blockchains reward rollup validators with their native tokens and provide a cross-rollup bridge maintained by their validators . We plan to take a closer look and elaborate in future articles.

Posted by:CoinYuppie,Reprinted with attribution to:
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