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What's the scariest thing about serverless?

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@slobodan_ Long-running tasks?

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@slobodan_ Compliance?

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@slobodan_ Using binaries and large dependencies?

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@slobodan_ Coldstart?

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@slobodan_ Cold start with VPC?

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@slobodan_ Local development and debugging?

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@slobodan_ Losing control?

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@slobodan_ Node.js?

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@slobodan_ But, what about…

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@slobodan_ BIG

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@slobodan_ BAD

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@slobodan_ VENDOR LOCK-IN

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@slobodan_ What is vendor lock-in?

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@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."

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@slobodan_

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@slobodan_

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@slobodan_

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

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

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

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

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

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

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

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

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@slobodan_ But what if Jeff is actually a villain?

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@slobodan_ Your wallet would not be happy…

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

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

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

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

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

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@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

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@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

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@slobodan_ Howtofight vendorlock-in?

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@slobodan_ Or, how to keep your switching costs reasonable?

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@slobodan_ • Planning and analysis • Good architecture • Deployment procedures How likely wi! I n"d to switch? What would be the cost?

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@slobodan_ That leads us to our topic…

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Writing testable serverless apps and preventing vendor lock-in using hexagonal architecture

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@slobodan_ But, before we continue…

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

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@slobodan_ Writing testable serverless apps using hexagonal architecture

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@slobodan_ Why is testing important for serverless apps?

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

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

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@slobodan_ An Example: Vacation Tracker

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@slobodan_ VacationTracker.io

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@slobodan_

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@slobodan_ Integrations can change or fail every moment!

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@slobodan_

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@slobodan_

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@slobodan_

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@slobodan_

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@slobodan_

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

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@slobodan_ But how do we prevent changes?

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@slobodan_ We can't. Our app needs to adapt fast! But we'! discuss that later today.

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

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@slobodan_ Testing pyramid

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@slobodan_

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@slobodan_ Testing pyramid vs "Serverless testing pyramid"

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@slobodan_

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

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@slobodan_ Writing testable serverless apps using hexagonal architecture

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

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

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

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

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@slobodan_ Risks to consider when building a serverless app

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

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@slobodan_ One of the architectures that fits these needs is Hexagonal Architecture or Ports and Adapters

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@slobodan_ Writing testable serverless apps using hexagonal architecture

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@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

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@slobodan_

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@slobodan_

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@slobodan_ Let's go back to Vacation Tracker for an example

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@slobodan_

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@slobodan_

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@slobodan_

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@slobodan_

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@slobodan_

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@slobodan_

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@slobodan_ Code, please!

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@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() }

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@slobodan_ await main(event, parseApiEvent, notification)

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@slobodan_ Unit tests

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@slobodan_ await main(event, parseApiEvent, notification) Mock notification repository instance Some static values Parser mock

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@slobodan_ Integration tests

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@slobodan_ await main(event, parseApiEvent, notification) Local notification adapter, using JS events for example Some static values Parser function

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@slobodan_ await main(event, parseApiEvent, notification) EventBridge notification adapter has its own integration tests

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@slobodan_ Simple and nice

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@slobodan_ What about End-to-End and UI tests?

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@slobodan_ Serverless is mainly a back end thing, but it can help with UI tests!

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@slobodan_ UI tests are slow and expensive

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@slobodan_ Benefits of serverless are cheap infrastructure and easy/fast parallelization

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@slobodan_

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@slobodan_ Or, you can use your favorite tool, such as cypress.io

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@slobodan_ But, do you remember…

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@slobodan_ BIG

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@slobodan_ BAD

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@slobodan_ VENDOR LOCK-IN

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@slobodan_

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@slobodan_ How does hexagonal architecture help you fightingvendorlock-in?

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@slobodan_ How does hexagonal architecture help you to keep switching costs reasonable?

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@slobodan_ Story time

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@slobodan_ Vacation Tracker VacationTracker.io

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

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@slobodan_ + A few bad decisions as a bonus :)

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@slobodan_ We did a few migrations in past few months.

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@slobodan_ • Express API -> Serverless API migration • MongoDB -> DynamoDB migration For example:

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

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@slobodan_ We defined an interface for our MongoDB Repository.

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@slobodan_ For example, this: Returns a single user with its properties. const db = new MongoDbRepository(something) const user = db.getUser(userId)

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@slobodan_ We created DynamoDB Repository with the same interface.

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@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:

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@slobodan_ So we simply did the following:

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@slobodan_

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@slobodan_

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@slobodan_

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@slobodan_ But, how does this look like?

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

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

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

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@slobodan_ And we lived happily ever after…

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@slobodan_ Writing testable serverless apps using hexagonal architecture Beyond testing

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@slobodan_ What should we do with things that can't be tested? For example, Slack changes an API while your app is in production

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

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@slobodan_ Monitoring/error-tracking tools

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

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@slobodan_ Serverless apps often heavily relies on front end, make sure you track front end errors too!

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@slobodan_ Also, services are smaller and smaller, but integrations require fine grained permissions.

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@slobodan_ There are tools that can help you to improve your permissions and keep your app secure.* * Protego, Puresec, and others.

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@slobodan_ But sometimes even monitoring can't help you!

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@slobodan_ You'll need a direct communication with your end users all the time!

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@slobodan_

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@slobodan_ Summary

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@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

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@slobodan_