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.

Core Components

`NodeMode`

The node’s operational mode is expressed by the NodeMode enum, carried on the node’s EngineConfig:

pub enum NodeMode {
    /// Validator mode.
    Validator,
    /// Sequencer mode.
    Sequencer,
}

`SequencerActor`

The core actor responsible for block production. Like every node component, it implements the NodeActor trait:

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

`SequencerConfig`

Sequencer behavior is configured through the SequencerConfig struct:

pub struct SequencerConfig {
    /// Whether or not the sequencer is enabled at startup.
    pub sequencer_stopped: bool,
    /// Whether or not the sequencer is in recovery mode.
    pub sequencer_recovery_mode: bool,
    /// The Url for the conductor RPC endpoint. If Some, enables the conductor service.
    pub conductor_rpc_url: Option<Url>,
    /// The confirmation delay for the sequencer.
    pub l1_conf_delay: u64,
}

Programmatic Configuration

Using the RollupNodeBuilder

To configure a Kona node programmatically for sequencer mode, set NodeMode::Sequencer on the EngineConfig and pass a SequencerConfig to the RollupNodeBuilder:

use kona_node_service::{NodeMode, RollupNodeBuilder, SequencerConfig};

// 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()
    ),
    l1_conf_delay: 4,                   // L1 origin confirmation delay
};

// engine_config carries `mode: NodeMode::Sequencer` along with the
// L2 engine URL, JWT secret, and L1 RPC URL.
RollupNodeBuilder::new(
    rollup_config,
    l1_config_builder,
    l2_trust_rpc,
    engine_config,
    p2p_config,
    rpc_config,
)
.with_sequencer_config(sequencer_config)
.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`
`l1_conf_delay`	Confirmation delay for L1 origin selection	`0`

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.

Getting Started

Guides

Tutorials

Kona Node

op-reth

Reference

Sequencer Mode

Overview

Core Components

`NodeMode`

`SequencerActor`

`SequencerConfig`

Programmatic Configuration

Using the RollupNodeBuilder

Configuration Options

Next Steps

​Overview

​Core Components

​NodeMode

​SequencerActor

​SequencerConfig

​Programmatic Configuration

​Using the RollupNodeBuilder

​Configuration Options

​Next Steps

Overview

Core Components

`NodeMode`

`SequencerActor`

`SequencerConfig`

Programmatic Configuration

Using the RollupNodeBuilder

Configuration Options

Next Steps