System Design BASICS: Horizontal vs. Vertical Scaling

This video is on the basics of system design.

If you have never designed a system before, this is probably the place to start.

So imagine you have a computer with you in which you have written an algorithm.

So some code is running on this computer and this code is like a normal function. It takes some input and it gives out an output.

Now people look at this code and they decide that this is really useful to them.

So they're ready to pay you so that they can use that code.

Now you cannot go around giving your computer to everybody.

So what you do is you expose your code using some protocol, which is going to be running on the internet, and by exposing your code using something called an a p i application programmable interface, when your code does run, it'll give an output and instead of storing that in the file or storing it in some database or something like that, you return that and that's called a response. Interestingly,

the thing that is sent to you is called a request where people request you. So that's what it is. There's a request sent, and for each request, there's a corresponding response that your computer will be sending back.

Imagine setting up this computer.

It might require a database to be connected to it.

It's within the desktop itself.

You might require to configure these endpoints that people are connecting to.

And you also need to take into consideration what happens if there's a power loss. If someone pulls the plug or something like that,

loss. If someone pulls the plug or something like that, you cannot afford to have your service go down because there's lots of people paying money for you. You should host your services on the cloud.

So what's the difference between a desktop and a cloud? Nothing really.

The cloud is a set of computers that somebody provides to you for money, of course. So if you pay a cloud solution, for example,

of course. So if you pay a cloud solution, for example, Amazon Web Services, which is the most popular one, if you pay these guys, they're going to give you computation power.

Computation power is nothing but a desktop that they have somewhere which can run your algorithm. How will you actually store your algorithm in that desktop?

Well, you can do something like a remote login into that desktop. That's what the cloud is. It's a set of desktops,

desktop. That's what the cloud is. It's a set of desktops, not necessarily desktops, but a set of computers that you can use to run your service.

The reason we like to do this is because the configuration, the settings the reliability can be taken care of to a large extent by the solution providers.

So now that we have our server hosted on a cloud, which is basically some computer that we don't know about, we can focus on the business requirements.

What business requirements could we possibly have? Well,

there's lots of people who are using algorithm now, and it gets to a point where the code that you have running on the machine is not able to handle all of these connections. So what do you do?

One of the solutions is to buy a bigger machine, Right?

This is solution number one. The solution number two is to buy more machines.

The ability to handle more requests by buying more machines or buying bigger machines is called scalability.

And this is a very important term that we need to understand. Well,

like we said, we can handle more requests by throwing more money at the problem.

When you're buying bigger machines, it means that your computer's going to be larger and therefore it can process the requests faster. So that is called vertical scaling.

And when you're buying more machines, it means that the request can fall on any one of these machines and it'll be processed, but because you have more of them, the requests can be randomly distributed amongst the machines that you have just bought. And that is called horizontal scaling.

bought. And that is called horizontal scaling.

These are two mechanisms by which you can increase the scalability of your system. Like we said, scalability is being able to handle more requests.

system. Like we said, scalability is being able to handle more requests.

Like any two approaches, we can compare them with the pros and cons.

The first one that we have talked about is we need some sort of load balancing here. Well, that's not the case here.

here. Well, that's not the case here.

If you have a single machine, there's no load to balance as such.

The second point is that with lots of machines, if one of the machine fails, you can redirect the request to the other ones.

While over here, there's a single point of failure.

So this is a single point failure and here it is resilient. The third thing to note is that all the communication that we have between the servers will be over the network and network calls us slow.

It's io while over here you have interprocess communication.

So that is quite fast. So here,

there is interprocess communication.

While over here we have network calls Between two services. So that is remote procedure calls.

So this is slow and this is fast.

The fourth point is data consistency. For example,

let's say you are having a transaction where 3 cents some data to four and then 4 cents it to five and 5 cents it to one.

Here you see that the data is complicated to maintain.

If there is a transaction where the operation has to be atomic, what could happen is that we have to lock all the servers, right?

All the databases that they're using, which is impractical.

So usually what happens is we have some sort of loose transactional guarantee, and that's, that's the reason why here, the data consistency is a real issue.

While over here, there's just one system on which all the data rec resides, and that's why this is consistent.

The final point deals with some hardware limitations that you're gonna have because we cannot just make the computer bigger and bigger and bigger and solve the problem. There's going to be some hardware limit that we have here.

the problem. There's going to be some hardware limit that we have here.

Point number five, and over here, this scales well in the sense that the, the amount of servers that you throw at the problem is almost linear in terms of how many users are added.

These are the five key differences that vertical scaling and horizontal scaling have. So what do you think is used in the real world? Both.

have. So what do you think is used in the real world? Both.

we take some of the good qualities of vertical scaling, which is really fast into process communication and the data being consistent.

So the cache is going to be consistent. There's no dirty reads, dirty rights, so to speak.

We take these two good qualities from here and we take these two good qualities from here, which is it scales well because the, there's a hardware limit over here and it's also resilient in the sense that if one of the server crashes, somebody else can come up. Okay?

So the hybrid solution is essentially horizontal scaling only, where each machine has a big box.

I mean each machine, you try to take as big a box as possible, as feasible money-wise. And then we, we pick up a solution this way.

Initially you can vertical scale as much as you like later on when the users start trusting you, you should probably go for horizontal scaling.

So these are the major considerations we have when designing a system.

Is it scalable? Is it resilient? And is it consistent with these qualities? There's always gonna be some trade-offs that we have, and that's what system design is.

We design a system which is going to meet the requirements, and the requirements are such that it's going to be Computer science way is possible to actually build a system like this.

If you have any doubts or suggestions, you can leave them in the comments below.

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