A Lambda which serves GraphQL requests using Postgraphile

postgraphile-lambda.js

import get from 'lodash/get'
import { graphql } from 'graphql'
import Pool from 'pg-pool'
import {
  createPostGraphileSchema,
  withPostGraphileContext
} from 'postgraphile'

import config from './config'

const postgraphileSchemaPromise = createPostGraphileSchema(
  config.DB_ENDPOINT,
  'public'
)

const pool = new Pool({
  user: config.DB_USER,
  password: config.DB_PASSWORD,
  host: config.DB_HOST,
  port: config.DB_PORT,
  database: config.DB_NAME,
  // this ensures the pool can drop a connection if it has gone bad
  min: 0,
  // no need for more since we are in Lambda-land
  max: 1
})

export default async function graphQLambda(event) {
  // grab the user ID from the request, this example assumes you're using Cognito
  const userId = get(event, 'requestContext.authorizer.claims.sub')
  const graphqlInput = JSON.parse(event.body)

  try {
    const postgraphileSchema = await postgraphileSchemaPromise
    const result = await withPostGraphileContext(
      {
        pgPool: pool,
        pgDefaultRole: 'application_user',
        pgSettings: {
          // the same setting we are using in our policies
          'user_id': userId
        }
      },
      async context => {
        return await graphql(
          postgraphileSchema,
          graphqlInput.query,
          null,
          { ...context },
          graphqlInput.variables,
          graphqlInput.operationName
        )
      }
    )

    return {
      headers: {
        'Access-Control-Allow-Origin': '*',
        'Access-Control-Allow-Credentials': true
      },
      body: JSON.stringify(result),
      statusCode: 200
    }
  } catch (error) {
    return {
      headers: {
        'Access-Control-Allow-Origin': '*',
        'Access-Control-Allow-Credentials': true
      },
      body: JSON.stringify(error),
      statusCode: 500
    }
  }
}