1. Introduction

This RFC proposes "rollup-boost," a new component for the OpStack ecosystem that enables external block building. By introducing a middleman between existing components, rollup-boost aims to increase flexibility in block production without major system changes. This solution addresses current limitations in transaction ordering and block creation, bringing OpStack closer to emerging standards in Ethereum Layer 1. Rollup-boost seeks to enhance the system's capabilities while maintaining its core integrity and security.

2. Goals/Non-goals

Goals:

• Describe how to perform external block building with op-node.
• Utilize only the Engine API to perform operations.

Non-goals:

• Discuss other APIs such as Builder API or any specific APIs outside of Engine API.
• Discuss any specific block building algorithms.
• Discuss any TEE specific deployments.

3. Background

Op-stack architecture

OpStack follows the Consensus Layer (CL) <> Execution Layer (EL) method, similar to Ethereum's architecture. In this system:

• The blockchain state lives in the EL node.
• The CL node (op-node in OpStack) decides which blocks are included.
• The EL node executes the chain and the blocks, but the CL node drives the process.
• The CL node relies on the EL node to validate payload validity, as it cannot determine this without execution.

This interaction primarily uses the engine_ namespace, along with a few eth_ calls for sync purposes. The main engine_methods are:

1. engine_newPayload: The CL sends a block to the EL for execution. It returns whether the block was valid or not, without changing the chain.