What is the default network that truffle migrates to when the config has 2 networks

Question

For the following truffle-config.js file, which has 2 networks listed in module.exports (development and ropsten), if I use the command truffle migrate in the terminal without explicitly saying --network development or --network ropsten, which network will the contract deploy to? Both?

require('dotenv').config();
const Web3 = require("web3");
const web3 = new Web3();
const WalletProvider = require("truffle-wallet-provider");
const Wallet = require('ethereumjs-wallet');

const ropstenPrivateKey = new Buffer(process.env.ROPSTEN_PRIVATE_KEY, "hex")
const ropstenWallet = Wallet.fromPrivateKey(ropstenPrivateKey);
const ropstenProvider = new WalletProvider(ropstenWallet, `https://ropsten.infura.io/${process.env.INFURA_ROPSTEN_ID}`);

module.exports = {
  networks: {
    development: {
      host: "127.0.0.1",
      port: 7545,
      network_id: "*" // Match any network id
    },
    ropsten: {
      provider: ropstenProvider,
      gas: 4600000,
      gasPrice: web3.utils.toWei('55', 'gwei'),
      network_id: "3"
    }
  }
};

Answer 1

If --network is unspecified, it deploys to only development. You can confirm this by just running a migrate:

$ truffle migrate
Compiling .\contracts\SimpleContract.sol...
Writing artifacts to .\build\contracts

Using network 'development'.

Network up to date.