Optimism Documentation

The Kona node can operate in sequencer mode to build and produce new L2 blocks. In this mode, the node acts as the sequencer for an OP Stack rollup, building L2 blocks on top of the current unsafe head and extending the L2 chain. This page explains the design of sequencer mode and how to configure it programmatically through the Node SDK. To run kona-node as a sequencer from the command line, follow the run a sequencer node guide.

Overview

When running in sequencer mode, the Kona node:

Builds L2 blocks by collecting transactions from the mempool and constructing new blocks
Selects L1 origins for new L2 blocks based on finalized L1 data
Manages block production timing and ensures proper sequencing constraints
Integrates with conductor services for leader election in multi-sequencer setups
Handles recovery scenarios when the sequencer needs to catch up with L1

The sequencer uses the same core derivation pipeline as validator nodes but operates in reverse - instead of deriving L2 blocks from L1 data, it produces L2 blocks that will later be derivable from L1.

Trait Abstractions

Core Interfaces

The sequencer functionality is built around several key trait abstractions:

`RollupNodeService`

The main service trait that defines the node’s operational mode and actor types:

pub trait RollupNodeService {
    type SequencerActor: NodeActor<
        Error: Display,
        OutboundData = SequencerContext,
        Builder: AttributesBuilderConfig<AB = Self::AttributesBuilder>,
        InboundData = SequencerInboundData,
    >;

    fn mode(&self) -> NodeMode;
    // ... other methods
}

`AttributesBuilderConfig`

Configures how L2 block attributes are constructed:

pub trait AttributesBuilderConfig {
    type AB: AttributesBuilder;
    fn build(self) -> Self::AB;
}

`SequencerActor`

The core actor responsible for block production:

Builds L2 blocks using the AttributesBuilder
Manages timing and L1 origin selection
Handles admin RPC commands for sequencer control
Coordinates with conductor services for leader election

Programmatic Configuration

Using the RollupNodeBuilder

To configure a Kona node programmatically for sequencer mode:

use kona_node_service::{NodeMode, RollupNode, SequencerConfig};
use url::Url;

// Configure sequencer settings
let sequencer_config = SequencerConfig {
    sequencer_stopped: false,           // Start sequencer immediately
    sequencer_recovery_mode: false,     // Normal operation mode
    conductor_rpc_url: Some(            // Optional conductor integration
        Url::parse("http://conductor:8080").unwrap()
    ),
};

// Build and start the sequencer node
let node = RollupNode::builder(rollup_config)
    .with_mode(NodeMode::Sequencer)                    // Enable sequencer mode
    .with_sequencer_config(sequencer_config)           // Apply sequencer settings
    .with_l1_provider_rpc_url(l1_rpc_url)             // L1 data source
    .with_l2_engine_rpc_url(l2_engine_url)            // L2 execution engine
    .with_jwt_secret(jwt_secret)                       // Engine API authentication
    // ... other configuration
    .build()
    .start()
    .await?;

Configuration Options

Field	Description	Default
`sequencer_stopped`	Start sequencer in stopped state	`false`
`sequencer_recovery_mode`	Enable recovery mode for catch-up	`false`
`conductor_rpc_url`	Conductor service endpoint for leader election	`None`

Next Steps

To run a sequencer from the command line, including the required flags and example configurations, see run a sequencer node.
For the full CLI flag catalogue, see the Kona node CLI reference.

Overview

Kona - Introduction

Kona - Kona for Node Operators

Kona - Kona as a Library

Kona - RFC

op-reth - Introduction

op-reth - Running op-reth

op-reth - CLI Reference

op-alloy - Introduction

op-alloy - Building

op-alloy - Reference

op-revm

Sequencer Mode

Overview

Trait Abstractions

Core Interfaces

`RollupNodeService`

`AttributesBuilderConfig`

`SequencerActor`

Programmatic Configuration

Using the RollupNodeBuilder

Configuration Options

Next Steps

​Overview

​Trait Abstractions

​Core Interfaces

​RollupNodeService

​AttributesBuilderConfig

​SequencerActor

​Programmatic Configuration

​Using the RollupNodeBuilder

​Configuration Options

​Next Steps

Overview

Trait Abstractions

Core Interfaces

`RollupNodeService`

`AttributesBuilderConfig`

`SequencerActor`

Programmatic Configuration

Using the RollupNodeBuilder

Configuration Options

Next Steps