apollo-server-lambda-middleware.js

const { Client } = require('pg')
const config = require('./config')
const generateServer = require('./server')

const server = generateServer()

const invokeHandler = (event, context, handler) => {
  return new Promise((resolve, reject) => {
    const callback = (error, body) => (error ? reject(error) : resolve(body))
    handler(event, context, callback)
  })
}

exports.graphqlHandler = async (event, context) => {
  const graphqlHandler = server.createHandler({
    cors: {
      origin: '*',
      credentials: true
    }
  })

  const client = new Client(config.db)

  let response
  try {
    await client.connect()

    response = await invokeHandler(
      event,
      { ...context, client },
      graphqlHandler
    )
  } catch (error) {
    console.error(error)
    throw new Error(error.message)
  } finally {
    await client.end()
  }

  return response
}