Rpc_nodes

Chapter 18: RPC Nodes & APIs

Overview

RPC Nodes (Remote Procedure Call nodes) are specialized blockchain nodes that expose APIs for external applications to interact with the blockchain. Understanding RPC nodes is essential as they’re commonly used in production environments.

18.1 What is an RPC Node?

An RPC node is a full node that provides API endpoints for:

┌─────────────────────────────────────────────────────────────────────────────┐
│                         RPC NODE FUNCTION                                   │
├─────────────────────────────────────────────────────────────────────────────┤
│                                                                              │
│   External Applications                                                      │
│   ┌─────────┐  ┌─────────┐  ┌─────────┐  ┌─────────┐  ┌─────────┐       │
│   │  dApp   │  │ Wallet  │  │ Explorer│  │Trading  │  │  Bot    │       │
│   └────┬────┘  └────┬────┘  └────┬────┘  └────┬────┘  └────┬────┘       │
│        │             │             │             │             │            │
│        └─────────────┴─────────────┴─────────────┴─────────────┘            │
│                                    │                                        │
│                                    ▼                                        │
│   ┌───────────────────────────────────────────────────────────────────┐     │
│   │                       RPC NODE                                     │     │
│   │   ┌─────────────┐  ┌─────────────┐  ┌─────────────┐            │     │
│   │   │   JSON-RPC  │  │  WebSocket  │  │  REST API   │            │     │
│   │   │   Server    │  │   Server    │  │   Server    │            │     │
│   │   └──────┬──────┘  └──────┬──────┘  └──────┬──────┘            │     │
│   │          │                │                │                     │     │
│   │          └────────────────┼────────────────┘                     │     │
│   │                           ▼                                         │     │
│   │                    ┌─────────────┐                                 │     │
│   │                    │  Full Node  │                                 │     │
│   │                    │ (Execution) │                                 │     │
│   │                    └──────┬──────┘                                 │     │
│   └───────────────────────────┼────────────────────────────────────────┘     │
│                               │                                           │
│                               ▼                                           │
│   ┌───────────────────────────────────────────────────────────────────┐     │
│   │                    P2P NETWORK                                     │     │
│   └───────────────────────────────────────────────────────────────────┘     │
│                                                                              │
└─────────────────────────────────────────────────────────────────────────────┘

Use Cases

Use Case	Description
dApps	Connect frontend to blockchain
Wallets	Query balances, broadcast transactions
Explorers	Display transaction history
Trading Bots	Execute automated trades
Analytics	Track on-chain metrics

18.2 JSON-RPC

What is JSON-RPC?

JSON-RPC is a stateless, lightweight remote procedure call (RPC) protocol for JSON-encoded messages.

Request Format

{
  "jsonrpc": "2.0",
  "method": "method_name",
  "params": ["param1", "param2"],
  "id": 1
}

Response Format

{
  "jsonrpc": "2.0",
  "result": "returned_value",
  "id": 1
}

Error Response

{
  "jsonrpc": "2.0",
  "error": {
    "code": -32600,
    "message": "Invalid Request"
  },
  "id": 1
}

18.3 Common JSON-RPC Methods

Ethereum JSON-RPC Methods

┌─────────────────────────────────────────────────────────────────────────────┐
│                    ETHEREUM JSON-RPC METHODS                                │
├─────────────────────────────────────────────────────────────────────────────┤
│                                                                              │
│  BLOCKS & HEADERS                                                           │
│  ──────────────────────────────────────────────────────────────────────     │
│  eth_blockNumber            → Get latest block number                     │
│  eth_getBlockByNumber       → Get block by number                         │
│  eth_getBlockByHash         → Get block by hash                            │
│  eth_getBlockTransactionCountByNumber → Count txs in block                │
│                                                                              │
│  TRANSACTIONS                                                               │
│  ──────────────────────────────────────────────────────────────────────     │
│  eth_sendRawTransaction     → Broadcast signed transaction                │
│  eth_getTransactionByHash   → Get transaction by hash                     │
│  eth_getTransactionReceipt  → Get transaction receipt                      │
│  eth_estimateGas           → Estimate gas needed                          │
│                                                                              │
│  STATE & BALANCES                                                           │
│  ──────────────────────────────────────────────────────────────────────     │
│  eth_getBalance             → Get account balance                         │
│  eth_getCode                → Get contract bytecode                       │
│  eth_getStorageAt           → Get storage slot value                      │
│  eth_call                   → Execute call without mining                 │
│                                                                              │
│  ACCOUNTS                                                                   │
│  ──────────────────────────────────────────────────────────────────────     │
│  eth_accounts               → List available accounts                     │
│  eth_sign                  → Sign message                                 │
│                                                                              │
│  NETWORK                                                                    │
│  ──────────────────────────────────────────────────────────────────────     │
│  net_version                → Get network ID                              │
│  net_peerCount             → Get peer count                               │
│  eth_protocolVersion       → Get protocol version                        │
│                                                                              │
└─────────────────────────────────────────────────────────────────────────────┘

Examples

# Get latest block number
curl -X POST http://localhost:8545 \
  -H "Content-Type: application/json" \
  -d '{
    "jsonrpc": "2.0",
    "method": "eth_blockNumber",
    "params": [],
    "id": 1
  }'

# Response:
# {"jsonrpc":"2.0","result":"0x10d4f1e","id":1}
# = 17720222 in decimal

# Get block by number (latest)
curl -X POST http://localhost:8545 \
  -H "Content-Type: application/json" \
  -d '{
    "jsonrpc": "2.0",
    "method": "eth_getBlockByNumber",
    "params": ["latest", false],
    "id": 1
  }'

# Get account balance
curl -X POST http://localhost:8545 \
  -H "Content-Type: application/json" \
  -d '{
    "jsonrpc": "2.0",
    "method": "eth_getBalance",
    "params": ["0x742d35Cc6634C0532925a3b844Bc9e7595f1e3E4", "latest"],
    "id": 1
  }'

# Send transaction (broadcast signed tx)
curl -X POST http://localhost:8545 \
  -H "Content-Type: application/json" \
  -d '{
    "jsonrpc": "2.0",
    "method": "eth_sendRawTransaction",
    "params": ["0x..."],
    "id": 1
  }'

18.4 Setting Up an RPC Node

Basic Configuration

# Start Geth as RPC node
geth \
  --syncmode snap \
  --http \
  --http.addr 0.0.0.0 \
  --http.port 8545 \
  --http.api eth,net,web3,debug,txpool \
  --http.corsdomain "*" \
  --ws \
  --ws.addr 0.0.0.0 \
  --ws.port 8546 \
  --ws.api eth,net,web3 \
  --ws.origins "*" \
  --datadir /data/ethereum \
  --maxpeers 100

Production Configuration

geth \
  --syncmode snap \
  --http \
  --http.addr 127.0.0.1 \
  --http.port 8545 \
  --http.api eth,net,web3,debug,txpool \
  --http.vhosts "localhost,yourdomain.com" \
  --http.ratelimit 1000 \
  --http.ratelimitburst 2000 \
  --ws \
  --ws.addr 127.0.0.1 \
  --ws.port 8546 \
  --ws.api eth,net,web3 \
  --ws.origins "https://your-dapp.com" \
  --ws.ratelimit 500 \
  --datadir /data/ethereum \
  --port 30303 \
  --maxpeers 100 \
  --cache 8192

18.5 WebSocket Connections

Why WebSockets?

┌─────────────────────────────────────────────────────────────────┐
│              HTTP VS WEBSOCKET                                    │
├─────────────────────────────────────────────────────────────────┤
│                                                                  │
│   HTTP/RPC                      WebSocket                        │
│   ─────────                     ────────                         │
│   Request-Response              Persistent Connection            │
│   One-time calls               Real-time updates                │
│   Polling needed               Push-based notifications         │
│   Good for queries             Good for live data               │
│                                                                  │
│   Use Cases:                    Use Cases:                       │
│   - Get balance                - Transaction confirmations       │
│   - Send tx                    - New block notifications          │
│   - Query history              - Mempool updates                 │
│                                                                  │
└─────────────────────────────────────────────────────────────────┘

WebSocket Example

// Connect to WebSocket
const ws = new WebSocket('ws://localhost:8546');

// Subscribe to new blocks
ws.onopen = () => {
  ws.send(JSON.stringify({
    jsonrpc: '2.0',
    method: 'eth_subscribe',
    params: ['newHeads'],
    id: 1
  }));
};

// Receive new blocks
ws.onmessage = (event) => {
  const message = JSON.parse(event.data);
  console.log('New block:', message.params.result);
};

HTTP Long Polling

If WebSocket isn’t available, use long polling:

// Simple polling for new blocks
async function pollBlock() {
  while (true) {
    const response = await fetch('https://your-rpc.com', {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({
        jsonrpc: '2.0',
        method: 'eth_blockNumber',
        params: [],
        id: 1
      })
    });
    const data = await response.json();
    console.log('Block:', parseInt(data.result, 16));
    await sleep(15000); // Poll every 15 seconds
  }
}

18.6 Rate Limiting

Why Rate Limit?

Prevent abuse
Protect node resources
Ensure fair access
DDoS protection

Rate Limit Headers

# Example: Ngnix rate limiting
limit_req_zone $binary_remote_addr zone=eth_rpc:10m rate=100r/s;

server {
    location / {
        limit_req zone=eth_rpc burst=200;
        proxy_pass http://localhost:8545;
    }
}

Nginx Configuration for RPC

upstream geth_backend {
    server 127.0.0.1:8545;
}

limit_req_zone $binary_remote_addr zone=api_limit:10m rate=100r/s;
limit_req_zone $binary_remote_addr zone=eth_call_limit:10m rate=50r/s;

server {
    listen 443 ssl http2;
    server_name rpc.yourdomain.com;

    ssl_certificate /etc/ssl/certs/your-cert.crt;
    ssl_certificate_key /etc/ssl/private/your-key.key;

    # Rate limiting
    limit_req zone=api_limit burst=200 nodelay;

    location / {
        proxy_pass http://geth_backend;
        proxy_http_version 1.1;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;

        # Timeouts
        proxy_connect_timeout 60s;
        proxy_send_timeout 60s;
        proxy_read_timeout 60s;
    }
}

18.7 Load Balancing Multiple RPC Nodes

Architecture

┌─────────────────────────────────────────────────────────────────────────────┐
│                    LOAD BALANCED RPC                                         │
├─────────────────────────────────────────────────────────────────────────────┤
│                                                                              │
│                              ┌─────────────────┐                             │
│                              │  Load Balancer  │                             │
│                              │   (Nginx/HAProxy)                             │
│                              └────────┬────────┘                             │
│                                       │                                      │
│           ┌───────────────────────────┼───────────────────────────┐         │
│           │                           │                           │         │
│           ▼                           ▼                           ▼         │
│   ┌───────────────┐          ┌───────────────┐          ┌───────────────┐ │
│   │   RPC Node 1  │          │   RPC Node 2  │          │   RPC Node 3  │ │
│   │   (Geth)      │          │   (Erigon)     │          │   (Geth)      │ │
│   └───────────────┘          └───────────────┘          └───────────────┘ │
│                                                                              │
└─────────────────────────────────────────────────────────────────────────────┘

HAProxy Configuration

frontend eth_rpc
    bind :443 ssl crt /etc/ssl/certs/server.pem
    default_backend geth_nodes

backend geth_nodes
    balance roundrobin
    option httpchk GET /health

    server geth1 10.0.0.1:8545 check inter 5s rise 2 fall 3
    server geth2 10.0.0.2:8545 check inter 5s rise 2 fall 3
    server geth3 10.0.0.3:8545 check inter 5s rise 2 fall 3

18.8 Public RPC Endpoints

Ethereum Mainnet Public RPCs

Provider	URL	Notes
Infura	`https://mainnet.infura.io/v3/YOUR_KEY`	Free tier available
Alchemy	`https://eth-mainnet.g.alchemy.com/v2/YOUR_KEY`	Free tier available
Ankr	`https://rpc.ankr.com/eth`	Free, rate limited
Cloudflare	`https://cloudflare-eth.com`	Free
QuickNode	`https://rpc-mainnet.moonvail.xyz`	Free tier

Testnet RPCs

Network	RPC URL
Sepolia	`https://rpc.sepolia.org`
Goerli	`https://rpc.goerli.org`
Holesky	`https://rpc.holesky.ethpandaops.io`

18.9 Interview Questions

Question	Answer
What is an RPC node?	A node that exposes APIs for external applications
Difference between HTTP and WebSocket?	HTTP is request-response; WebSocket is persistent connection
How to protect RPC endpoints?	Rate limiting, authentication, TLS
What is JSON-RPC?	JSON-based remote procedure call protocol

Summary

RPC nodes expose APIs for blockchain interaction
JSON-RPC is the standard protocol
WebSockets enable real-time updates
Production needs: rate limiting, load balancing, security
Popular providers: Infura, Alchemy, Ankr

Next Chapter

In Chapter 19: JSON-RPC API Methods, we’ll explore more detailed API methods.

Last Updated: 2026-02-20