> ## Documentation Index
> Fetch the complete documentation index at: https://docs.optimism.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Node Design Overview

The entry-point for the `kona-node` is the [`RollupNode`][node] service,
which encapsulates the core wiring for the node. A `RollupNode` is
constructed through the [`RollupNodeBuilder`][builder], and its
[`start` method][start] handles connecting all the different components
of the node, running each in a spawned task. As such, each node
component is considered an actor.

The `RollupNode` abstracts individual actors through the
[`NodeActor` trait][actor], 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 `NodeActor`s required to run a
`RollupNode`. Actors are defined in the [actors][actors] module of the
`kona-node-service` crate, and the `RollupNode` wiring lives in the
[service][service] 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 [`RollupNode`][node] 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][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.
  A companion engine RPC actor serves read-only engine
  queries. The [engine][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.
* **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][p2p]
  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][sequencer] docs.
* **RPC Actor**: The RPC actor spins up and serves an
  RPC server that exposes the rpc methods required by
  the [OP Stack Specs][specs].

[p2p]: ./p2p

[engine]: ./engine

[derivation]: ./derivation

[sequencer]: ./sequencer

[specs]: https://specs.optimism.io/protocol/rollup-node.html

[service]: https://github.com/ethereum-optimism/optimism/tree/develop/rust/kona/crates/node/service/src/service

[actors]: https://github.com/ethereum-optimism/optimism/tree/develop/rust/kona/crates/node/service/src/actors

[actor]: https://github.com/ethereum-optimism/optimism/blob/develop/rust/kona/crates/node/service/src/actors/traits.rs

[start]: https://github.com/ethereum-optimism/optimism/blob/develop/rust/kona/crates/node/service/src/service/node.rs

[node]: https://github.com/ethereum-optimism/optimism/blob/develop/rust/kona/crates/node/service/src/service/node.rs

[builder]: https://github.com/ethereum-optimism/optimism/blob/develop/rust/kona/crates/node/service/src/service/builder.rs