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The entry-point for the kona-node is the RollupNode service, which encapsulates the core wiring for the node. A RollupNode is constructed through the RollupNodeBuilder, and its start method handles connecting the different components of the node and running its actors in spawned tasks. The RollupNode abstracts individual actors through the NodeActor trait, a minimal interface with a single step method that the service drives in a loop until the actor reports a fatal error or the node shuts down. Kona provides implementations for all NodeActors required to run a RollupNode. Actors are defined in the actors module of the kona-node-service crate, and the RollupNode wiring lives in the service module.

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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 RollupNode builds and starts the following actors.
  • 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 priority order against the EL client. Read-only engine queries are served directly by RollupRpc. The engine docs expand on this.
  • L1 Watcher Actor: Watches the L1 chain for new head and finalized blocks and relays them to the derivation actor. It also keeps the unsafe block signer current from the SystemConfig contract, for gossip validation and the signer actor.
  • 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.
  • 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 docs.
  • Signer Actor: Runs alongside the sequencer actor. It signs each block the sequencer builds, in order, and passes it to the network actor to gossip.
  • RPC Actor: Supervises the JSON-RPC server and handles restarts. Jsonrpsee dispatches requests to the registered modules, including RollupRpc, which serves the rollup methods required by the OP Stack Specs.