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Writing Testable Serverless Apps Using Hexagona...

Writing Testable Serverless Apps Using Hexagonal Architecture @ TestJS Summit 2021

Slobodan Stojanović

January 29, 2021
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  1. @slobodan_ "In economics, vendor lock-in, makes a customer dependent on

    a vendor for products and services, unable to use another vendor without substantial switching costs."
  2. @slobodan_ "My train of thought went like this: the term

    “lock-in” is misleading. We are really talking about switching costs." Mark Schwartz Enterprise Strategist at AWS
  3. @slobodan_ "As soon as you commit yourself to a platform

    or a vendor you will have switching costs if you later decide to change." Mark Schwartz Enterprise Strategist at AWS
  4. @slobodan_ • Planning and analysis • Good architecture • Deployment

    procedures How likely wi! I n"d to switch? What would be the cost?
  5. Slobodan Stojanovic CTO @ Cloud Horizon & CTO @ Vacation

    Tracker co-author of Serverless Applications with Node.js book AWS Serverless Hero https://slobodan.me
  6. @slobodan_ Most of the time serverless apps are not fully

    isolated monoliths without integrations
  7. @slobodan_ Integration tests are cheaper, but also more important, because

    the common serverless app is split into many small pieces
  8. @slobodan_ Not to another cloud vendor, but to your new

    service, new or changed integration…
  9. @slobodan_ One of the architectures that fits these needs is

    Hexagonal Architecture or Ports and Adapters
  10. @slobodan_ "Allow an application to equally be driven by users,

    programs, automated test or batch scripts, and to be developed and tested in isolation from its eventual run-time devices and databases." Alistair Cockburn Creator of Hexagonal architecture
  11. @slobodan_ const { httpResponse, parseApiEvent, EventBridgeRepository } = require('../common') const

    main = require('./main') export async function handler(event) { // Create instance of SNS notification repository const notification = new EventBridgeRepository( process.env.topic ) // Invoke main function with all dependencies await main(event, parseApiEvent, notification) return httpResponse() }
  12. @slobodan_ • Serverless prototype • Small team (1 fulltime developer)

    • Initial product was Serverless chatbot + Express.js and MongoDB • Growing fast (200+ teams using it)
  13. @slobodan_ • Express API -> Serverless API migration • MongoDB

    -> DynamoDB migration • API Gateway -> AppSync and GraphQL For example:
  14. @slobodan_ For example, this: Returns a single user with its

    properties. const db = new MongoDbRepository(something) const user = db.getUser(userId)
  15. @slobodan_ Returns a single user with the same properties. const

    mdb = new MongoDbRepository(something) const ddb = new DynamoDbRepository(somethingElse) const user1 = mdb.getUser(userId) const user2 = ddb.getUser(userId) expect(user1).toEqual(user2) // They are equal! For example, this:
  16. @slobodan_ describe('DynamoDB repository', () => { beforeAll(() => { //

    Create test DB }) afterAll(() => { // Destroy test DB }) // Tests })
  17. @slobodan_ beforeAll(async () => { const params = { ...

    } await dynamoDb.createTable(params).promise() await dynamoDb.waitFor('tableExists', { TableName: tableName }).promise() })
  18. @slobodan_ afterAll(async () => { await dynamoDb.deleteTable({ TableName: tableName }).promise()

    await dynamoDb.waitFor('tableNotExists', { TableName: tableName }).promise() })
  19. @slobodan_ • Good architecture helps you to maintain your switching

    costs low (or at least reasonable) • Hexagonal architecture is a nice fit for serverless apps • Test your integrations (and app in general) • Testing is not enough, you'll need monitoring and error tracking for your serverless apps