NestJS Enterprise Backend APIs · Lesson

Deployment to Testnets & Mainnet

Understand the process of deploying your DApps to public testnets for final testing and ultimately to the Ethereum mainnet.

Deployment to Testnets & Mainnet is a free NestJS Enterprise Backend APIs lesson on CoddyKit — lesson 6 of 6. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the NestJS Enterprise Backend APIs learning path, one of 6 lessons in the course, and your progress syncs across the web and the CoddyKit app.

What is DApp Deployment?

Welcome! Today, we'll learn about deploying Decentralized Applications (DApps). Deployment is the process of publishing your smart contracts and associated front-end code to a blockchain network.

It's a crucial step that makes your DApp accessible to users worldwide. Without deployment, your DApp remains just code on your computer.

Why Deploy to Testnets First?

Before launching your DApp to the world, it's vital to test it thoroughly. This is where testnets come in!

Testnets are separate blockchain networks that mimic the main Ethereum network.
They use 'test Ether' (fake currency) for transactions, so you can test without risking real funds.
This allows developers to find and fix bugs, ensuring the DApp works as expected.

Key Ethereum Testnets

Ethereum has several public testnets. The most prominent one currently is Sepolia.

Sepolia: This is the recommended testnet for new development. It's a proof-of-stake network, like the Ethereum mainnet.
Historically, there were others like Goerli, but Sepolia is now the primary choice for testing smart contracts and DApps.

Connecting to a Testnet

To deploy to a testnet, your development environment (like Hardhat or Truffle) needs to connect to it. This is usually done via an RPC URL provided by a service like Infura or Alchemy.

These services act as a gateway, allowing your tools to communicate with the blockchain without running a full node yourself. You'll need an API key for access.

Getting Test Ether (Faucets)

On a testnet, every transaction (including contract deployment) requires gas, paid in test Ether. You can get free test Ether from a faucet.

A faucet is a web service that sends small amounts of test Ether to your wallet address. Simply visit a Sepolia faucet website, enter your address, and request funds.

Deployment Scripts

Deploying smart contracts manually can be tedious. That's why we use deployment scripts, typically written in JavaScript.

These scripts automate the process of compiling your contract, signing the transaction with your private key, and sending it to the chosen blockchain network (testnet or mainnet).

Understanding Gas for Deployment

Every operation on Ethereum, including contract deployment, consumes gas. Gas is a unit that measures the computational effort required.

Gas Limit: The maximum gas you're willing to spend.
Gas Price: How much Ether you're willing to pay per unit of gas.
Total Cost: Gas Limit × Gas Price.

Deployment is often one of the most gas-intensive transactions.

Connecting to a Network Example

Here's a simple JavaScript snippet using Ethers.js to connect to an Ethereum network and fetch its current block number. This is a foundational step for any deployment script.

Remember to replace YOUR_INFURA_API_KEY with your actual key.

const { ethers } = require("ethers");

async function main() {
  // Connect to a Sepolia testnet RPC (Infura example)
  const provider = new ethers.JsonRpcProvider("https://sepolia.infura.io/v3/YOUR_INFURA_API_KEY");

  try {
    const blockNumber = await provider.getBlockNumber();
    console.log("Connected to network. Current block number:", blockNumber);
  } catch (error) {
    console.error("Failed to connect or get block number:", error.message);
  }
}

main();

Deploying to Mainnet

Once your DApp is thoroughly tested on testnets, you might consider deploying to the Ethereum Mainnet. This is the live, public blockchain where real assets and value exist.

Real Funds: Mainnet deployments cost real Ether.
Security: Ensure extensive audits and testing have been completed.
Immutability: Once deployed, smart contracts are generally unchangeable.

Always proceed with extreme caution and ensure all configurations are correct!

Deployment Knowledge Check

You've learned about deploying DApps. Let's test your understanding!

Deployment Journey Recap

Well done! You've learned the essential steps for deploying DApps.

We started with testnets for safe, free testing.
We explored how to connect to networks and get test Ether.
You now understand the role of deployment scripts and gas costs.
Finally, we discussed the critical considerations for deploying to the mainnet.

This knowledge is fundamental for bringing your decentralized applications to life!

Frequently asked questions

Is the “Deployment to Testnets & Mainnet” lesson free?

Yes — the full text of “Deployment to Testnets & Mainnet” is free to read here on the web, and the NestJS Enterprise Backend APIs course includes 6 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the NestJS Enterprise Backend APIs course, upgrade to CoddyKit PRO.

What will I learn in “Deployment to Testnets & Mainnet”?

Understand the process of deploying your DApps to public testnets for final testing and ultimately to the Ethereum mainnet. You practise NestJS Enterprise Backend APIs with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start NestJS Enterprise Backend APIs?

No prior experience is required. NestJS Enterprise Backend APIs on CoddyKit is structured for beginners through advanced learners; this is — lesson 6 of 6, so you can start here or from the beginning and move at your own pace.

How long does the “Deployment to Testnets & Mainnet” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this NestJS Enterprise Backend APIs lesson?

Yes. Every NestJS Enterprise Backend APIs lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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