truffle.js

const KeystoreProvider = require("truffle-keystore-provider")
const Web3 = require("web3")

const memoizeProviderCreator = () => {
  let keystoreProviders = {}

  return (account, dataDir, providerUrl, readOnly) => {
    if (readOnly) {
      return new Web3.providers.HttpProvider(providerUrl)
    } else {
      if (providerUrl in keystoreProviders) {
        return keystoreProviders[providerUrl]
      } else {
        const provider = new KeystoreProvider(account, dataDir, providerUrl)
        keystoreProviders[providerUrl] = provider
        return provider
      }
    }
  }
}

const createProvider = memoizeProviderCreator()

module.exports = {
  networks: {
    dev: {
      host: "localhost",
      port: 8545,
      network_id: "*"
    },
    rinkeby: {
      provider: () => {
        return createProvider(process.env.RINKEBY_ACCOUNT, process.env.DATA_DIR, "https://rinkeby.infura.io", process.env.READ_ONLY)
      },
      network_id: 4,
      gas: 6600000
    },
    mainnet: {
      provider: () => {
        return createProvider(process.env.MAINNET_ACCOUNT, process.env.DATA_DIR, "https://mainnet.infura.io", process.env.READ_ONLY)
      },
      network_id: 1,
      gas: 6600000
    }
  }
}