Node Design Overview

The entry-point for the kona-node is the RollupNodeService trait which encapsulates the core wiring for the node. The default implementation of the trait start method handles connecting all the different components of the node, running each in a spawned thread. As such, each node component is considered an actor.

The RollupNodeService abstracts individual actors through the NodeActor trait. With the NodeActor trait, the RollupNodeService builds the actor and then starts it.

Kona provides implementations for all NodeActors required to run a RollupNodeService. Actors are defined in the actors module of the kona-node-service crate.

The kona-node is an implementation of the RollupNodeService that lives in the standard module.

Actors

The architecture of kona-node is a web of actors that share state through message passing, using channels, rather than using shared memory.

The RollupNodeService defines the set of required actors using associated types. These are subject to change, but are currently defined as follows.

• Derivation Actor: Orchestrates the derivation pipeline, deriving L2 payload attributes from l1 blocks. Payload attributes prepared this way are forwarded to the Engine Actor to be executed. The derivation docs dive deeper into how the derivation actor works.
• Engine Actor: Brokers the connection to the execution layer client (or "execution engine"). The engine actor turns messages from other actors into engine "tasks" that are executed in a round-robin against the EL client. The engine docs expand on this.
• Network Actor: Manages the P2P Network for the rollup node. The P2P stack consists of discv5 peer discovery and block gossip through libp2p. Visit the network docs for more detail.
• Supervisor Actor (beta): The supervisor actor is an interop feature that allows the kona-node to be "managed" (or "indexed") by the supervisor - a new component in the OP Stack. A detailed overview of interop and the supervisor's role is provided in the supervisor docs.
• Runtime Actor: Loads runtime values from the contracts on the L1 chain for the OP Stack. This is a very light-weight actor described in runtime docs.
• Sequencer Actor: The sequencer actor extends the kona-node to be run as a sequencer. Sequencing is periphery to the basic rollup node operation. See the sequencer.
• RPC Actor: The RPC actor spins up and serves an RPC server that exposes the rpc methods required by the OP Stack Specs.