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# System prepended metadata

title: 'Node and Client (Node architecture, Light Client, Archive Node, Bootnodes)'

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# Node Architecture


An Ethereum node is compos of two clients: 

1. Execution client 
2. Consensus client 

For a node to propose a new block, it must also run a validator client.

***What Does the Execution Client Do?***

 **1. The Execution Client:** is the part of Ethereum that runs smart contracts and handles transactions. It uses the Ethereum Virtual Machine (EVM) to process all the code and updates the state (like balances, contract data, etc.)
 
**What It Does:**
* Runs transactions and smart contracts
* Keeps track of Ethereum’s current state (who owns what)
* Creates execution payloads (the list of transactions and updated data)
* Re-checks transactions in new blocks
* Allows apps and wallets to connect through RPC (e.g. Metamask, Web3.js)

***What Does the Consensus Client Do?***

**2. The Consensus Client:** helps your Ethereum node stay in sync with the blockchain and follow the correct version of the chain.

 What It Does:
* Receives new blocks from other nodes
* Uses a fork choice algorithm to pick the best and correct chain
* Keeps your node updated with the latest block (chain head)
* Connects with other consensus clients through a special P2P network to share blocks and validator votes (called attestations)


***What is a Validator?***
**A Validator:** is a special part of the Ethereum network that helps keep it secure and running smoothly
To become a validator, you need to stake 32 ETH and run the validator software (which works with the consensus client).

***What Validators Do:***
* Attest (vote) for the correct blocks
* Propose new blocks when selected
* Earn rewards for doing their job well
* Get penalized or slashed for bad behavior (like being offline or dishonest)

###  Node Components (Simple Comparison)

| **Component**        | **What It Does (In Simple Terms)**                                                                                                                                                           |
| - | - |
| **Execution Client** |  Runs transactions & smart contracts using the EVM. <br> Shares transactions with others. <br> Builds execution data (payloads). <br> Lets apps/wallets talk to Ethereum (via RPC). |
| **Consensus Client** |  Chooses the correct chain (using fork choice). <br>Shares blocks & votes (attestations). <br>Tracks block finality & chain head.                                                    |
| **Validator**        |  Proposes new blocks. <br>Votes for good blocks (attestations). <br>Earns rewards or gets slashed. <br> Needs 32 ETH to start.                                                    |


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# Light Client 

### What is a Light Client?
A light client (or light node) is like a lite version of an Ethereum node.
Instead of downloading and storing all blockchain data, it just asks for the important stuff (like block headers) from a full node or server

Think of it like checking headlines instead of reading the whole newspaper 

***What Light Clients Do:***

* Follow the latest block by reading block headers
* Verify data using validator signatures (so it’s still secure)
* Save space and power  no need to store the full blockchain
* Can run on small devices like phones or browsers


***How They Work:***
* Every 1.1 days, Ethereum picks 512 validators to form a sync committee
* This committee signs new block headers
* Light clients only check these headers not full blocks
* They verify the committee signatures to make sure the data is legit

***What innovations do light clients enable?***
The primary benefit of light clients is enabling more people to access Ethereum independently with negligible hardware requirements and minimal reliance on third parties

***How Light Clients Help Rollups:***

* Rollups use bridges to move funds between Ethereum and the rollup.
* The problem: Oracles can lie and trick rollups into releasing money without a real deposit (hack risk ).
* The solution: A light client inside the rollup can verify deposits using proofs from Ethereum, instead of trusting oracles.
* This makes rollups more secure, and the same idea can help protect bridges between other blockchains too.


***How Light Clients Help Rollups Stay Safe:***

Rollups use bridges to move funds between Ethereum and the rollup.

*  Problem: Oracles used by rollups can lie and say a deposit happened leading to hacks and stolen funds.

* Solution: A light client inside the rollup can verify deposits with real proofs from Ethereum before releasing any money. No need to fully trust oracles.

This idea can also help secure bridges between other blockchains too.

### Current State of Light Clients
Light clients are still being developed they work, but most are not fully ready for everyday use yet.

Here are some being worked on:

* **Lodestar:** consensus light client (TypeScript)
* **Helios:** combined execution and consensus (Rust)
* **Geth (light mode):** execution client (Go)
* **Nimbus:** consensus light client (Nim)


# Ethereum Archive Node

***What Is an Ethereum Archive Node?***

An Archive Node is a special kind of Ethereum node that stores everything from the beginning of the blockchain not just the latest data, but every single change in state ever made.

*Think of it like a full blockchain time machine*

***What Is an Archive?***
The archive itself is a complete historical record. It keeps track of:

* Every balance ever held by any account
* Every smart contract’s storage at any point in time
* Every change to Ethereum’s state since genesis block (block 0)

| **Node Type**    | **What It Stores**                              |
| - |- |
| Full Node    | Only the latest state of Ethereum           |
| Archive Node | The entire state history from the beginning |


* A full node can tell you what your balance is now
* An archive node can tell you what it was at any past block


***How It Works***
* An archive node is a regular Ethereum client (like Geth or Besu), but it's set up with special config to build and keep all historical state.
* It builds a full state trie at every block that’s the detailed record of Ethereum’s state.
* This makes archive nodes very big in size several terabytes (TB) of data

***What It's Used For:***
*  Blockchain explorers (like Etherscan)
* Data analytics tools
* Research and debugging
* Verifying historical contract states or balances
* Some advanced smart contract systems (like rollups) may need them too


# Introduction to Ethereum Bootnodes

*Bootnodes are full nodes that u connect with is like a helper that help you to find and tell you this are the available network available or Is responsible for telling you and showing you the available networks*


Bootnodes are full nodes that are not behind a NAT (Network Address Translationopens in a new tab)
Every full node can act as a bootnode as long as it is publicly available

### TO BE CONTINUED NEXT CLASS.... !!