Design Blockchain RPC Service - System Design | WinJob

Problem Statement: Multi-Chain JSON-RPC at Scale

Design a production blockchain RPC platform (Infura / Alchemy / QuickNode class): multi-tenant JSON-RPC, WebSocket subscriptions, and fair routing to operator-run full nodes. This section covers problem statement: multi-chain json-rpc at scale during the understanding phase.

Operational detail

Anchor capacity: ~80k aggregate RPS, ~40k WebSocket connections, eth_getLogs ~15% of traffic. Expose X-Chain-Lag when serving behind tip; halt writes if backends disagree on block hash. Meter compute units: eth_call=16 CU, eth_getLogs=75 CU per 1k blocks, trace_*=500+ CU.

Failure and edge cases

Trace storms, log range scans, backend blackholes, and fork splits are daily incidents. Runbooks: drain backend, open circuit, shift WS coalescing group, notify tenant webhooks.

Interview checkpoints

javaOne Dark Pro

1 public record RouteKey(int chainId, String method, String tenantId) {}

pythonOne Dark Pro

1 def cu_weight(method: str, blocks: int) -> int:
2     weights = {'eth_call': 16, 'eth_getLogs': 75}
3     return weights.get(method, 10)

typescriptOne Dark Pro

1 export type RouteKey = { chainId: number; method: string; tenantId: string };

Why interviewers care

Blockchain RPC Service interviews reward crisp scope, explicit trade-offs, and failure stories—not generic microservice diagrams.

Interview checkpoint

Name one failure story for Problem Statement: Multi-Chain JSON-RPC at Scale that proves you understand real outages, not happy-path diagrams.

Key Highlights

•Managed RPC sits between dApps and operator-run full nodes—never replaces consensus
•Product promise: low-latency eth_* / JSON-RPC with multi-chain routing and metering
•Hot paths: eth_getBlockByNumber, eth_call, eth_sendRawTransaction, eth_getLogs, WS newHeads
•Revenue ties to compute units (CU) and websocket minutes—not flat bandwidth alone

1	def cu_weight(method: str, blocks: int) -> int:
2	weights = {'eth_call': 16, 'eth_getLogs': 75}
3	return weights.get(method, 10)