Sequencer Mode

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.

:::info Sequencer mode is an advanced configuration primarily used by rollup operators. Most users will run nodes in the default validator mode. :::

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

CLI Usage

Basic Sequencer Setup

To run a Kona node in sequencer mode:

kona-node node \
  --mode=Sequencer \
  --l1-eth-rpc=http://l1-node:8545 \
  --l1-beacon=http://l1-beacon:5052 \
  --l2-engine-rpc=http://l2-execution:8551 \
  --l2.jwt-secret=./jwt.hex \
  --chain=123456

Required Arguments

:::warning Required Configuration

Sequencer mode requires all standard node arguments plus the --mode=Sequencer flag. Missing any required argument will prevent the node from starting. :::

Argument	Flag	Environment Variable	Description
Mode	--mode	KONA_NODE_MODE	Must be set to Sequencer
L1 RPC	--l1-eth-rpc	KONA_NODE_L1_ETH_RPC	L1 execution client RPC URL
L1 Beacon	--l1-beacon	KONA_NODE_L1_BEACON	L1 beacon API URL
L2 Engine	--l2-engine-rpc	KONA_NODE_L2_ENGINE_RPC	L2 engine API endpoint
JWT Secret	--l2.jwt-secret	KONA_NODE_L2_ENGINE_AUTH	Path to JWT secret file
Chain ID	--chain	KONA_NODE_L2_CHAIN_ID	L2 chain identifier

Sequencer-Specific Flags

Flag	Environment Variable	Default	Description
--sequencer.stopped	KONA_NODE_SEQUENCER_STOPPED	false	Start sequencer in stopped state
--sequencer.max-safe-lag	KONA_NODE_SEQUENCER_MAX_SAFE_LAG	0	Max L2 blocks between safe and unsafe heads
--sequencer.l1-confs	KONA_NODE_SEQUENCER_L1_CONFS	4	L1 confirmations for origin selection
--sequencer.recover	KONA_NODE_SEQUENCER_RECOVER	false	Force recovery mode operation
--conductor.rpc	KONA_NODE_CONDUCTOR_RPC	-	Conductor service RPC endpoint
--conductor.rpc.timeout	KONA_NODE_CONDUCTOR_RPC_TIMEOUT	1	Conductor RPC timeout (seconds)

Example Configurations

Basic Sequencer

kona-node node \
  --mode=Sequencer \
  --l1-eth-rpc=http://localhost:8545 \
  --l1-beacon=http://localhost:5052 \
  --l2-engine-rpc=http://localhost:8551 \
  --chain=42161

Sequencer with Conductor

kona-node node \
  --mode=Sequencer \
  --conductor.rpc=http://conductor:8080 \
  --conductor.rpc.timeout=5 \
  --sequencer.l1-confs=6 \
  --l1-eth-rpc=http://l1-node:8545 \
  --l1-beacon=http://l1-beacon:5052 \
  --l2-engine-rpc=http://l2-execution:8551 \
  --chain=123456

Recovery Mode Sequencer

kona-node node \
  --mode=Sequencer \
  --sequencer.recover=true \
  --sequencer.max-safe-lag=100 \
  --l1-eth-rpc=http://localhost:8545 \
  --l1-beacon=http://localhost:5052 \
  --l2-engine-rpc=http://localhost:8551 \
  --chain=42161

Key Considerations

:::tip Sequencer Operation

• L1 Confirmations: The --sequencer.l1-confs setting determines how many L1 blocks the sequencer waits before using an L1 block as an origin. Higher values provide more safety but increase latency.
• Recovery Mode: Use --sequencer.recover=true when the sequencer needs to catch up after being offline.
• Conductor Integration: For multi-sequencer deployments, configure the conductor service for proper leader election. :::

Running a sequencer in production requires careful consideration of infrastructure, monitoring, and failover procedures. Ensure proper JWT secret management and secure network configuration.