In this article we discover what the sequencer node is, an essential part of the Ethereum -Rollup ecosystem.
This infrastructure entity is responsible for a series of processes that bring the transaction data on the L2 into the head -l1 and act as a connection point.
The operation and the degree of decentralization of the sequencer have a direct influence on safety, reliability and resistance to censorship of these solutions.
Let’s look at everything in detail below.
What is the sequencer and what is his role in the EVM world
In the landscape of scalability solutions for Ethereum, The sequencer is an entity that orders, carries out and aggregate off-chain transactions before publishing on the layer-1 blockchain,. The most important role is to improve the scalability and efficiency of Layer 2 solutions, such as rollups, by lowering gas costs and speeding up the transaction finishes.
Technically defined as a junction, the sequencer processes the transactions that are performed on the rollups and encapsulates them into a compressed “side. “Then it sends this data to Ethereum, where they are officially recorded and added to the primary chain that is responsible for security.
Depending on the architecture of Layer-2, the sequencer can be centralized or decentralized and can influence critical aspects, such as the order of transactions, data availability and censorship resistance.
In the case of Optimistic rollupAs arbitrum and optimism, the sequencer orders the TX and publishes them on Ethereum assuming that they are all valid, unless disputed. In ZK-RollupAs Starknet and ZKSync, the sequencer not only processes the transactions, but also generates cryptographic evidence that are then verified on Ethereum. Finally, in rollups of the Valid Type such as Zkfair and Rhino.fi, a hybrid process takes place because the data is partially off-chain verified.
It is important to emphasize that this figure is also used by other block chains and scalability solutions, but to prevent confusion, we will only concentrate on the EVM world in this article. For knowledge we point out There are components analogue to sequencers in ecosystems such as Cosmos, Avalanche subnets and Celestia.
The Workflow of Sequencers in the various Ethereum Rollups
We see that deeper into the different tasks performed by the sequencers, we see how they manage the life cycle of a transaction that is performed within a rollup.
We can group their workflow 3 Fundamental steps: Collecting and sorting transactions, implementation and publication about Ethereum.
1) Collecting and sorting transactions
Users send transactions to the sequencer instead of directly to the L1, which order them in a specific block according to an order strategy. In general we find a “in Rollups“Auction“Strategy, where an auction takes place to determine the implementation order (those who pay more reimbursements have priority and are first ordered).
Other strategies can be of the “Come first served first“Type, where transactions are accepted and processed in the order in which they arrive.
2) Implementation and calculation of the state
After determining the order of the transactions, the sequencer performs them locally, so that the status of the Rollup Off-Chain is updated.
This implementation is deterministic and follows the rules defined by the smart contract of the Rollup to L1, whereby the integrity of the operations is guaranteed.
3) Batch production and publication on L1
At this point the transactions were grouped in batches and sent to L1 Ethereum.
The sequencer only publishes the essential data (calldates) for data availability (DA), so that Ethereum can always reconstruct the state status. This step ensures that the minimum calculation of use is used to keep the L2 network costs low
Based on the Rollup type, these 3 steps can more or less vary considerably, as shown in the following table.
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The problem of centralization of sequencer
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At the moment, most sequencers on Ethereum have been centralizedBecause almost all Rollups have a single junction that is responsible for managing the connection between L2 and L1. This configuration is essential in the “Internship 0“Phases of rollups, where a compromise between decentralization and scalability is needed to make the entire infrastructure functional and efficient in the initial development phase.
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With the times go ahead with time, rollups are aimed at decentralizing their sequencers, introducing new solutions for sharing junctions and the federation, so that they are moved to “Phase 1“And”Phase 2. “In the meantime, the excessive centralization of sequencers, even for a limited period, could, however, cause serious structural problems for the relevant network at the second level.
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First of all, the entrance of the control to a single node introduces a “Only point of failure “: If the sequencer undergone an attack, a technical malfunction or a manipulation, the entire infrastructure could be affected, leading to transaction inputs or even interruptions on the service. Moreover, this power concentration can Risk of censorship on transactionsBecause the single operator would have the option of randomly excluding or re -ordering transactions, so that MEV strategies are applied.
Another critical aspect concerns to trust: The lack of a distributed validation mechanism makes it difficult for users to verify independently that transactions have been handled correctly. All this undermines the principle of decentralization that forms the basis of the philosophy of Ethereum.
The centralization of junctions represents a double-edged sword: the practical example of the Layer-2 Linea.
Excessive centralization of sequencers is configured as a two -edged sword, Able to literally save a full ecosystem from collapse, but at the same time able to lead to a strong random censorship of the network.
What happened with Layer-2 Linea in June last year, during the hack and exploitation of the Velocore protocol, is a clear example of this.
On that occasion, during the cyber attack on the DEX, the Consensys team (which manages the Linea Rollup) decided Stop Block Production, “to block“The sequencer. By doing this, practically frozen with the chain, the Velocare team managed to control the incident, so that the code -vulnerability was resolved. In the meantime, Consensys censored the address of the attacker, which made communication with the sequencer impossible (which, as we remember, validates transactions and sends to L1).
If the sequencer was not closed, there would have been very serious economic consequences, with effects, not only on linea, but also on Ethereum.
The hackers could have driven more money from the vulnerable smart contracts, leading to the exhaustion of the value of the assets based on linea. Moreover, the attacker could have changed the status of the network, making it more difficult to detect and resolve the problem.
This would have had consequences for other Defi protocols that are connected to linea, which means that many users suffer liquidations or irreversible losses.
The Velocore Hack event led the Ethereum community to think about the Delicate balance between security and decentralization. On the one hand, the rapid intervention of Consensys prevented a financial disaster that protected users and protocols against considerable losses. On the other hand, the closure of the sequencer and the censorship of the address of the attacker released their concern about the excessive centralized stream of Layer-2 operators.
