Blockchain Developer Decentralized Application Architecture Questions and Answers

Question 1

A development team is creating a decentralized social media platform where users can post messages and upload images.
To maintain decentralization and avoid high on-chain storage costs, where is the most appropriate place to store the user-uploaded images?

Accepted Answer

In a decentralized storage network like IPFS, with the content identifier (CID) stored on-chain.

Answer

Directly within the smart contract's state variables.

Answer

On a centralized server managed by the development team, with image hashes stored on-chain.

Answer

As event logs emitted by the smart contract.

Question 2

In a typical dApp architecture, how does the user's browser-based front-end (e.g., a React app) communicate with smart contracts deployed on the Ethereum blockchain?

Accepted Answer

Via a JavaScript library like Ethers.js or Web3.js, which connects to a blockchain node and interacts with the contract's ABI.

Answer

By making direct HTTP POST requests to the smart contract's address.

Answer

Through a centralized API server that translates requests into blockchain transactions.

Answer

Using a WebSocket connection directly to a mining pool.

Question 3

A smart contract for a decentralized insurance product needs to automatically trigger a payout based on real-world flight delay data. What architectural component is necessary to securely provide this external data to the smart contract?

Accepted Answer

A decentralized oracle network.

Answer

A client-side script that fetches the data and calls the contract.

Answer

A Layer 2 scaling solution like a rollup.

Answer

An off-chain database synchronized with the blockchain.

Question 4

Which of the following best describes the primary role of a service like Infura or Alchemy in the context of dApp architecture?

Accepted Answer

To offer a reliable and scalable connection to blockchain nodes via an API, removing the need for developers to run their own nodes.

Answer

To provide decentralized off-chain storage for dApp assets.

Answer

To act as a centralized authority for governing smart contract upgrades.

Answer

To automatically audit smart contract code for security vulnerabilities before deployment.

Question 5

A developer is building a high-frequency trading dApp where users need to perform many rapid, low-cost transactions. The main blockchain suffers from high gas fees and slow confirmation times. Which architectural solution is most suitable for this use case?

Accepted Answer

Using a Layer 2 scaling solution, such as state channels or rollups.

Answer

Deploying the entire application on a private, permissioned blockchain.

Answer

Increasing the gas price for every transaction to get priority from miners.

Answer

Storing all transaction data off-chain and settling only daily net balances.

Question 6

When designing a dApp, a developer decides to use a sidechain instead of a state channel for handling complex computations. What is a key architectural difference between a sidechain and a state channel?

Accepted Answer

Sidechains are separate blockchains with their own consensus mechanisms, while state channels are off-chain agreements between specific participants.

Answer

State channels are public and transparent, while sidechains are always private.

Answer

State channels require a trusted intermediary, whereas sidechains are completely trustless.

Answer

Sidechains post every transaction to the main chain, while state channels only post the final summary.