Decentralized Application Architecture Flashcards

What architectural problem does an oracle solve for a dApp?

Answer: It securely brings off-chain real-world data onto the blockchain

Oracles feed external data (prices, weather, events) to smart contracts, which cannot access off-chain data natively.

A dApp needs the current ETH/USD price for a lending protocol. What is the safest design choice?

Answer: Use a decentralized oracle network with multiple data sources

Decentralized oracle networks aggregate multiple sources to resist manipulation and single points of failure.

Why are smart contracts considered deterministic in dApp architecture?

Answer: Every node must produce the identical result given the same inputs and state

Determinism is required so all nodes reach consensus on the same state after execution.

What is a common reason to split a dApp's logic into a proxy contract and an implementation contract?

Answer: To enable upgradeability of the logic while preserving state and address

The proxy pattern keeps a stable address and storage while the implementation logic can be swapped/upgraded.

In an event-driven dApp frontend, how does the UI usually learn that an on-chain action succeeded?

Answer: By listening to events/logs emitted by the smart contract

Contracts emit events/logs that frontends and indexers subscribe to for state updates.

What does 'composability' mean in the context of dApp architecture?

Answer: Smart contracts can permissionlessly call and build on one another like money legos

Composability lets contracts interact and integrate freely, enabling DeFi 'money legos'.

Why might a dApp use a relayer to enable gasless (meta) transactions for users?

Answer: So users can sign transactions while a third party pays the gas, improving UX

Meta-transactions let a relayer submit and pay gas for a user-signed message, lowering onboarding friction.