Execution Layer¶

The Execution Layer (EL) is one of the core components of the Ethereum network after "The Merge" upgrade, formerly known as the Ethereum 1.0 chain. It is responsible for processing transactions, executing smart contract logic, and maintaining Ethereum's global state.

The Problem It Solves¶

During Ethereum's transition from Proof of Work (PoW) to Proof of Stake (PoS), a modular design approach was adopted to achieve a clearer architecture and a more efficient upgrade path. The core problem to be solved is separation of concerns:

Complexity Management: Decoupling complex consensus logic (who has the right to produce blocks) from state transition logic (what the block content is), allowing the two layers to be developed and optimized independently.
Client Diversity: Allowing different teams to focus on building either consensus clients or execution clients, reducing the risk of a single software stack.

Implementation Mechanisms and Principles¶

In the current Ethereum architecture, nodes typically run both an Execution Client and a Consensus Client (also known as a beacon node). The two communicate via the Engine API.

Division of Responsibilities¶

Execution Layer (EL):
- Transaction Pool Management: Receives, validates, and propagates user-broadcasted transactions (Gossip protocol).
- Block Building: Packages transactions and generates the block body (Payload).
- State Execution: Executes transactions through the Ethereum Virtual Machine (EVM), updating account balances, contract storage, and other world state trees.
- Data Storage: Maintains the blockchain's historical data and current state database.
Consensus Layer (CL):
- Responsible for Proof of Stake (PoS) logic, including validator management, fork choice rules (LMD GHOST), and block finality confirmation (Casper FFG).
- The CL directs the EL on when to build blocks and when to validate specific payloads.

Interaction Flow¶

When a validator is selected to propose a block: 1. Its consensus client requests the execution client to build an "execution payload" containing transactions. 2. The execution client packages transactions, executes them, and returns the result. 3. The consensus client includes this payload in a beacon block and broadcasts it across the network. 4. Other nodes' consensus clients receive the block and instruct their execution clients to verify the payload's validity.

Key Features¶

EVM Host: The execution layer is where the EVM actually runs, serving as the environment for all decentralized applications (DApps).
Modular Architecture: The execution layer can work with different consensus layers (or even Layer 2 sequencers). This flexibility is the foundation of Rollup scaling technology.
Rich Client Ecosystem: Current mainstream execution layer clients include Geth (Go), Nethermind (C#), Besu (Java), Reth (Rust), and Erigon (Go).