In this article, we discover what the sequencer node is an essential component of the Ethereum roller ecosystem.
This infrastructure entity is responsible for a series of processes that carry the transaction data made in the Main L1, acting as a connection point.
The operation and degree of decentralization of the sequencer directly affect the security, reliability and resistance to censorship of these solutions.
Let’s look at everything in detail below.
What is the sequencer and what is your role in the Evm world?
In the landscape of scalability solutions for Ethereum, The sequencer is an entity that orders, executes and adds transactions outside the chain before publishing them in the Capa-1 block chain. Its main role is to improve the scalability and efficiency of layer 2 solutions, such as rolls, reducing gas costs and the acceleration of the completion of the transaction.
Technically defined as a node, the sequencer processes the transactions executed in the Rollups and encapsulates them in a compressed “batch. “Then send this data to Ethereum, where they are officially registered and added to the main security chain.
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 Prolonged optimisticAs the referee and optimism, the sequencer orders the TX and publishes them in Ethereum assuming that they are valid unless they are disputed. In ZK-ROLUPHowever, such as Starknet and Zksync, the sequencer not only processes transactions but also generates cryptographic tests that are then verified in Ethereum. Finally, in the Rollups of the Validium Write as Zkfair and Rhino.FI, a hybrid process occurs since the data is partially verified outside the chain.
It is important to emphasize that this figure is also used by other blockchains and scalability solutions, but to avoid confusion, this article will focus only on the EVM world. For knowledge, we point out that There are similar components to sequencers in ecosystems such as Cosmos, Avalanche and Celestia subnets.
The workflow of the sequencers in the various Ethereum rollups
By immersing more in the various tasks performed by the sequencers, we see how they manage the life cycle of a transaction executed within a curled up.
We can group your workflow in 3 fundamental steps: The collection and classification of transactions, execution and publication on Ethereum.
1) Collection and classification of transactions
Users send transactions to the sequencer instead of directly to the L1, which orders them in a specific block according to an order strategy. In general, in the Rollups, we find a “Based on the auctionStrategy, where an auction takes place to determine the execution order (those who pay more rates have priority and are ordered first).
Other strategies can be from “First come for the first time“Type, where transactions are accepted and processed in the order that arrive.
2) Execution and calculation of the State
After deciding the order of the transactions, the sequencer executes them locally, updating the status of the chain outside the chain.
This execution is deterministic and follows the rules defined by the smart contract of the roll in L1, thus ensuring the integrity of the operations.
3) Production and batch publication in L1
At this point, transactions are grouped into lots and are sent to L1 Ethereum.
The public sequencer only the essential data (Calldata) for the availability of data (DA), ensuring that Ethereum can always rebuild the state in the chain. This step ensures that the minimum computing effort is used to keep the Red L2 low
Depending on the type of accumulation, these 3 steps may vary more or less significantly, as shown in the following table.
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| Type of roll | Data collection | Execution | Publication in L1 |
| Prolonged optimistic (Referee, optimism) | The sequencer collects transactions sent by users. | The sequencer orders and executes the transactions, then publishes them in lots. | The data is published in the chain and the transactions are accepted after the challenge period |
| ZK-ROLUP (Starknet, Zksync) | The sequencer collects transactions, creating a data batch for processing. | The sequencer executes the transactions and generates a ZK proof validity to demonstrate the validity. | The cryptographic test guarantees the validity of transactions, without the need for a challenge |
| Validium (Starkex) | The sequencer collects the transaction data but keeps them out of the chain. | The sequencer executes transactions outside the chain and updates the state. | The data is not completely in the chain, reducing costs, but with less security compared to those curled up in the chain. |
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The problem of centralization of the sequencer
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At the moment, most sequencers in Ethereum are centralizedsince almost all Rollups have a single node responsible for administering the connection between L2 and L1. This configuration is essential in the “Stage 0“Phases of the Rollups, where a commitment between decentralization and scalability is necessary for all the infrastructure to be functional and efficient in its initial development phase.
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Advancing over time, Rollups are aimedStage 1” and “Stage 2. “Meanwhile, however, excessive centralization of sequencers, even for a limited period of time, could create serious structural problems for the second level network in question.
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First, trusting a single node control presents a “Single Failure Point “: If the sequencer suffered an attack, a technical failure or a handlingAll infrastructure could be compromised, which leads to transaction delays or even service interruptions. In addition, this concentration of power could facilitate the Risk of censorship in transactionsSince the single operator would have the ability to exclude or reorder transactions arbitrarily, applying MEV strategies.
Another critical aspect refers 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 is at the base of Ethereum’s philosophy.
The centralization of the nodes represents a double -edged sword: the practical example of layer 2 line.
The excessive centralization of the sequencers is configured as a double -edged sword, Able to literally save a complete ecosystem of collapse, but at the same time capable of leading to strongly arbitrary censorship of the network.
What happened with the line of layer 2 in June of last year, during the trick and exploit of the Velocore protocol, is a clear example of this.
On that occasion, during the cyber attack against the DEX, the consensys team (which manages the line roll) decided Stop block production, “off“Your sequencer. In doing so, with the practically frozen chain, Velocare’s team managed to contain the incident, solving the vulnerability of the code found. Meanwhile, Consensys censored the attacker’s address, making communication with the sequencer impossible (as we remember, validate transactions and send them to L1).
If the sequencer had not closed, there would have been very serious economic consequences, with impacts not only online, but also in Ethereum.
Computer pirates could have drained more funds from vulnerable intelligent contracts, which leads to the depletion of the value of assets based on line. In addition, the attacker could have altered the state of the network, which makes it more difficult to detect and solve the problem.
This would have had repercussions on other protocols defined to line, which makes many users suffer from irreversible liquidations or losses.
Velocore’s Hack event led to the Ethereum community to reflect on the Delicate balance between security and decentralization. On the one hand, the rapid intervention of Consensy avoided a financial disaster, protecting users and significant loss protocols. On the other hand, the closure of the sequencer and the censorship of the attacker’s direction expressed concerns about the excessive power of the operators of layer 2.
