Designing testable serverless apps using hexagonal architecture

What's the scariest thing about serverless?

@slobodan_ Long-running tasks?

@slobodan_ Compliance?

@slobodan_ Using binaries and large dependencies?

@slobodan_ Cold start?

@slobodan_ Cold start with VPN?

@slobodan_ Node.js?

@slobodan_ But, what about…

@slobodan_ BIG

@slobodan_ BAD

@slobodan_ VENDOR LOCK-IN

@slobodan_

@slobodan_ What is vendor lock-in?

@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."

@slobodan_

@slobodan_ A guy with a lot of servers.  Let's call
him Jeff.

@slobodan_ Jeff is smart, and he knows how do you
use his servers.

@slobodan_ But what if Jeff is actually a villain?

@slobodan_ Your wallet would not be happy…

@slobodan_

@slobodan_ Another guy with a lot of servers.  Let's call
him Bill.

@slobodan_ That's vendor lock-in in the cloud

@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

@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

@slobodan_ How to fight vendor lock-in?

@slobodan_ Or how to keep your switching costs reasonable?

@slobodan_ • Planning and analysis • Good architecture • Deployment
procedures How likely will I need to switch? What would be the cost?

@slobodan_ That leads us to our topic…

Designing testable serverless apps using hexagonal architecture

@slobodan_ But, before we continue…

Slobodan Stojanovic CTO @ Cloud Horizon & CTO @ Vacation
Tracker co-author of Serverless Applications with Node.js book AWS Serverless Hero @slobodan_ serverless.pub

@slobodan_ Designing testable serverless apps using hexagonal architecture

@slobodan_ Why is testing important for serverless apps?

@slobodan_ Most of the time serverless apps are not fully
isolated monoliths without integrations

@slobodan_ Instead, they contain many services interacting with each other
and with external dependencies

@slobodan_

@slobodan_ Integrations can change every moment!

@slobodan_ Tests don't prevent changes. They make sure your changes
are not accidental.

@slobodan_ But how do you know what should you test
in a serverless app?

@slobodan_ Testing pyramid

@slobodan_

@slobodan_ Testing pyramid vs "Serverless testing pyramid"

@slobodan_

@slobodan_ Integration tests are cheaper, but also more important, because
the common serverless app is split into many small pieces

@slobodan_ Ok, so which architecture is the best for serverless
apps?

@slobodan_ Any architecture that will let you test your serverless
app easily and keep switching costs low.

@slobodan_ Because sooner or later you'll need to switch/migrate pieces
of your app.

@slobodan_ Not to another cloud vendor, but to your new
service, new or changed integration…

@slobodan_ Risks to consider when building a serverless app

@slobodan_ • configuration risks • technical workflow risks • business
logic risks • integration risks

@slobodan_ One of the app architectures that fits these needs
is  hexagonal architecture

@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

@slobodan_

@slobodan_ An example

@slobodan_

@slobodan_ Code, please

@slobodan_ const {  httpResponse, parseApiEvent,  SnsRepository  } = require('../common')  const
main = require('./main')  async function handler(event) { const { body, headers } = parseApiEvent(event) // Create instance of SNS notification repository  const notification = new SnsRepository(  process.env.topic ) // Invoke main function with all dependencies  await main(body, headers, notification)  return httpResponse()  }

@slobodan_ await main(body, headers, notification)

@slobodan_ Unit tests

@slobodan_ await main(body, headers, mockNotification) Mock notification repository instance Some
static values

@slobodan_ Integration tests

@slobodan_ await main(body, headers, localNotification) Local notification adapter, using JS
events for example Some static values

@slobodan_ Simple and nice

@slobodan_ But, do you remember…

@slobodan_ BIG

@slobodan_ BAD

@slobodan_ VENDOR LOCK-IN

@slobodan_

@slobodan_ How does hexagonal architecture help you fighting vendor lock-in?

@slobodan_ Story time

@slobodan_ Vacation Tracker vacationtracker.io

@slobodan_ vacationtracker.io

@slobodan_ • Serverless prototype • Small team (1 fulltime developer)
• Initial product was Serverless chatbot + Express.js and MongoDB • Growing fast (200+ teams using it)

@slobodan_ • Express -> Serverless migration • MongoDB -> DynamoDB
migration

@slobodan_ Let's talk about MongoDB -> DynamoDB switch

@slobodan_

@slobodan_ How does this look like?

@slobodan_ describe('DynamoDB repository', () => { describe('unit', () => {
... }) describe('integration', () => { beforeAll(() => { // Create test DB }) afterAll(() => { // Destroy test DB }) // Tests }) })

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

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

@slobodan_ And they lived happily ever after…

@slobodan_ Beyond testing

@slobodan_ What should we do with things that can't be
tested?

@slobodan_ What should we do with things that can't be
tested? For example, Google or someone else deprecated an API while your app is in production

@slobodan_ Make sure you are monitoring your app and tracking
errors

@slobodan_ Monitoring/error-tracking tools

@slobodan_ • Built-in tools (CloudWatch, X-Ray) • Epsagon • IOpipe
• Thundra • Lumigo • and many others

@slobodan_ Serverless apps often heavily relies on front end, in
those cases you need to track front end errors as well

@slobodan_ desole.io

@slobodan_

@slobodan_ Summary

@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

@slobodan_ Links to the things I mentioned

@slobodan_ • Mark Schwartz - Switching Costs and Lock-In: amzn.to/2S4iT3G
• Hexagonal Architecture: bit.ly/hex-arch • Vacation Tracker: vacationtracker.io • Hexagonal Architecture at Vacation Tracker: bit.ly/vt-hex-arch • Desole (error-tracking tool): desole.io

@slobodan_ One more thing!

@slobodan_

@slobodan_ Serverless Applications with Node.js Use claudia40 promo code for
40% off serverless.pub/book @slobodan_

@slobodan_ Thank you!

@slobodan_ Thank you! Danke

Designing testable serverless apps using hexago...

Designing testable serverless apps using hexagonal architecture

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