Writing Testable Serverless Apps Using Hexagonal Architecture

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According to many polls, testing serverless applications and fear of the cloud vendor lock-in are among the top five challenges organizations face when adopting serverless. We often hear that using serverless effectively requires a mind shift. But what does that mean? Do we need new tools and strategies for testing serverless applications, or can we use existing tools we already use for our non-serverless applications? And what about cloud vendor lock-in? Is that a real thing or just a fictional story that scares people away from serverless? Can we decrease a risk of vendor lock-in using a well-known architecture, such as hexagonal architecture?

Slobodan Stojanović
Slobodan Stojanović
28 min
15 Jun, 2021

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Video Summary and Transcription

The scariest thing about serverless is the fear of vendor lock-in and losing control. Planning, good architecture, and deployment procedures help keep switching costs reasonable. Hexagonal architecture is a useful approach for writing testable serverless apps. Integration testing is crucial for serverless apps, and hexagonal architecture helps fight vendor lock-in and reduce switching costs. Docker is used for testing serverless functions, and the practicality of hexagonal architecture remains a question.

1. The Scariest Thing About Serverless

Short description:

The scariest thing about serverless is losing control and the fear of vendor lock-in. Vendor lock-in refers to being dependent on a specific vendor for products or services, making it difficult to switch to another vendor without significant costs. Let's explain this with a server rental analogy. You rent a server from a guy named Jeff, who provides additional services like databases and caching. However, if Jeff increases the prices or becomes unreliable, you have the option to switch to another provider like Bill. But migrating your application to a different provider can be time-consuming and costly. This is what we call cloud vendor lock-in.

Hello. What's the scariest thing about serverless? There are many scary things, right? Well, some people would say that the scariest thing is long-running tasks, but that's not really the scariest thing because there are many ways to have longer-running functions and things like this. Have you heard about cold start? That was a really scary thing at the beginning, but now it's not that much because with Node.js, your cold start is maybe 100 milliseconds or something like that.

What about local development and debugging? That's still really hard thing to do but tooling is getting better every day so it's not really that scary anymore. But there's one thing that everyone is mentioning, it's losing control. Yeah, maybe, but on the other side, with losing control, you're gaining speed and some other things. So I don't think that's the scariest thing. But again, there's one thing that everyone is scared about and it doesn't matter if you talk to developer or some business person, everyone will mention big bad vendor lock-in. It's really scary, right?

But let's see what's vendor lock-in. If you go to Wikipedia, you'll see that in economics, vendor lock-in makes a customer dependent on a vendor for products or services unable to use another vendor without substantial switching costs. I don't really like the definition so let's try to explain with a few diagrams. So let's say that you need a server. I don't know why, but you just want to have a server and build some kind of application. You can buy it or rent it, but no one is buying servers anymore. So you decide to rent it. You find a guy that has a lot of servers in his basement, let's call that guy Jeff, and you rent one server from Jeff and that's now your cloud. You're using that server and after some time, Jeff is really smart and he knows how to use his servers and he knows that you're building databases, some caching and things like this. So he starts building services for you. You can use just a database without the server or just use cache or maybe machine learning or functions. And it's even better because you can pay for these things only when you use them. It's really awesome and he will love your cloud services now. But what if Jeff is actually a villain and at some point you're so dependent that he'd services and he increased costs of all of these services. And of course your wallet would not be happy in this moment and you will not be happy for sure. But fortunately you have some options. For example, you can find another guy that has a lot of servers in his basement or whatever, let's call this one Bill And Bill also has a database and compute and machine learning and everything else. And the costs are more or less the same as the cost of Jeff's services before he increased the pricing. But what's expensive is migration because Jeff's database is not exactly the same as Bill's database. So you need to invest a lot of time to move your application from one services to other. And that's basically cloud vendor lock in. We saw another example lately with Parler, but that's likely different because they're not able to migrate to any big vendor.

2. Switching Costs and Testable Serverless Apps

Short description:

Vendor lock-in refers to switching costs when changing platforms or vendors. Planning, good architecture, and deployment procedures help keep switching costs reasonable. Today's topic is writing testable serverless apps using hexagonal architecture. Testing is important for serverless apps as you still own your code and business logic. Serverless apps often have small services with external dependencies. For example, our WebApp with a Slack chatbot allows users to request vacation with a few clicks.

So this is really extreme case, but this presentation will not cover that. Regarding vendor lock-in, I really think that Mark Schwartz, enterprise strategist at AWS is right. He thinks that term lock-in is misleading because we're actually talking about switching costs. As soon as we commit to any platform or a vendor, we'll have switching costs if we later decide to change that vendor or platform. For example, if you build your application in PHP, and then at some point you want to migrate that to Node.js or Go or something else, you'll have a big switching cost because you need to pause for some time, rebuild everything in a different language, and then continue from that point.

So, how do we fight vendor lock-in, or let's ask the better question, how do we keep our switching costs reasonable? Well, we can do a few things. First, we need to do planning and analysis. For example, we need to answer some questions such as how likely will I need to switch to another platform or service? What would be the cost for that switch? If there is no big chance to switch to something else, for example, you picked your database and you don't think you will need to switch in the near future, it's okay to have a slightly higher cost of migration, but for some other things, you need to keep that cost lower. You need to have a good architecture, of course. And finally, you need to have deployment procedures because if you don't have them, it will be really, really hard to migrate anywhere.

That leads us to our topic for today, and that's writing testable serverless applications and preventing vendor lock-in using hexagonal architecture. But before we continue, let me introduce myself. I'm Slobodan Stanovich, I'm CTO and partner at Cloud Horizon and VacationTracker, VacationTracker is a lead tracking management system and Cloud Horizon is basically an agency we are doing web apps for other people. I also wrote the book, Serverless Applications with Node.js with my friend Alexander Simovich, and it's published by many publications. And I'm also AWS serverless hero. You can follow me on my website. I write about serverless a lot and testing also. So let's go back to our topic because that's definitely more interesting than I am. So we'll talk about writing testable serverless apps using hexagonal architecture. But let's focus on testable part first. Why is testing important for serverless apps? You basically outsource some parts of your app to a vendor, but that's not covering everything. They'll manage infrastructure for you, but you still own your code and your business logic. So you need to test that part of the application. And also most of the time serverless applications are not fully isolated monoliths without integrations. Instead, there contain a lot of small services that are interacting with each other all the time, and they have a lot of external dependencies. I mentioned vacation tracker, so here's an example. Our application is WebApp that has also Slack chatbot. And inside Slack, you can type slash vacation and request vacation in just a few clicks. It's so easy, you can do that in just a few minutes, actually a few seconds. But in the background, that looks something like this.

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