What Is Rollup Node?

Rollups write transaction data to a main chain such as Ethereum; however, separate software is needed to compute the rollup's current state, meaning account balances and contract data, from this data. A rollup node reads the relevant transactions and blob data on the main chain, reprocesses them according to the rollup's rules, and builds the rollup chain's blocks on its own side. Wallets and applications also connect to the rollup through the RPC interfaces these nodes provide.

For example, on OP Stack-based networks, this task is handled by a component called 'op-node', which works together with an EVM-compatible execution client; the result is a structure similar to the consensus and execution client split on Ethereum. On Arbitrum, a similar function is performed by the Nitro node software. Some nodes also take on the sequencer role, while most serve only a verification and data-serving function.

The existence of independent rollup nodes is important for a rollup's transparency. By running their own nodes, users and developers can verify the state published by the sequencer instead of blindly accepting it; on optimistic rollups, being able to challenge incorrect states also depends on this verification. Rollup nodes also need access to a trusted main chain node.