How to explain vertical and horizontal scaling in the cloud


In this world of cloud, one of the biggest features is the ability to scale. There are different ways to accomplish scaling, which is a transformation that enlarges or diminishes. One is vertical scaling and the other is horizontal scaling.

What is the difference between the two? If you look at just the definitions of vertical and horizontal you might see the following:

• Vertical: something that is standing directly upright at a right angle to the flat ground
• Horizontal: something that is parallel to the horizon (the area where the sky seems to meet the earth)

If you are a visual kind of person you may be able to see this. Let’s add some technology to this and see what we get.

(Related: How cloud computing helps businesses scale)

modern buildingsVertical scaling can essentially resize your server with no change to your code. It is the ability to increase the capacity of existing hardware or software by adding resources. Vertical scaling is limited by the fact that you can only get as big as the size of the server.

Horizontal scaling affords the ability to scale wider to deal with traffic. It is the ability to connect multiple hardware or software entities, such as servers, so that they work as a single logical unit. This kind of scale cannot be implemented at a moment’s notice.

So, having said all that, I always like to provide an example that you might be able to visually imagine.

Imagine, if you will, an apartment building that has many rooms and floors where people move in and out all the time. In this apartment building, 200 spaces are available but not all are taken at one time. So, in a sense, the apartment scales vertically as more people come and there are rooms to accommodate them. As long as the 200-space capacity is not exceeded, life is good.

This could even apply to a restaurant. You have seen the signs that tell you how many people could be held in the establishment. As more patrons come in more tables may be set up and more chairs added (scaling vertically). However when capacity is reached no more patrons would be able to fit. You can only be as big as the building and patio of the restaurant. This is much like in your cloud environment, where you could add more hardware to the existing machine (RAM and hard drive space) but you are limited to capacity of your actual machine.

cloud scalingOn the horizontal scaling side, imagine a two lane expressway. The expressway is good to handle the 2,000 or so vehicles that travel the expressway. As commerce begins to expand, more buildings are constructed and more homes are built. As a result the expressway that once handled 2,000 or so vehicles is now having an increase to 8,000 vehicles. This makes a major traffic jam during rush hour. To alleviate this problem of traffic jams and an increase in accidents, the expressway can be scaled horizontally by constructing more lanes and quite possibly adding an overpass. In this example the construction will take some time. Much like scaling your cloud horizontally, you add additional machines to your environment (scaling wider). This requires planning and making sure you have resources available as well as making sure your architecture can handle the scalability.

I think this could be a simple way to explain scalability to a customer if they wanted to know the difference between vertical and horizontal scaling in the cloud. What are your thoughts? How have you described scalability? Leave a comment below and let me know.

Comments: 2
David Beaumont

About David Beaumont

David Beaumont is a Staff Software Engineer with IBM. In this role, David is a contributor in the Managed Service area where he provides client support to a number of clients with regard to EDI and SaaS related services. David is a qualified support professional, HDI Certified and holds a Bachelor of Science in Business Administration, Finance from The Ohio State University. David has more than 15 years of experience in customer service, EDI and client support. To contact David please email Feel free to comment on his blog:
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2 Responses to How to explain vertical and horizontal scaling in the cloud

  1. cloudubq says:


    Nice explanation. I live in the SAP world, so we do a lot of both. We scale our application servers horizontally, but the database and central instance (DB/CI) server can only scale vertically. There are some horizontal scaling DB technologies, but we don't see much use of them other than for active-active system designs.

    When picking your cloud provider, it is very critical to understand your boundaries. For the the largest DB/CI which you'll scale vertically you'll want to know size of the largest box they offer and can I get to it smoothly should I need to scale up. For the application servers, you need to understand how strong the LAN in the data center is and when will I get to too many application servers (generally 5 – 7).

    Vertical and Horizontal are important and how your cloud provider provides is the key take away.

  2. Swaminathan S says:

    I am not sure the example you gave for horizontal vs. vertical was clear with respect to the cloud. Let me try as a guest to explain. I am by the way a software quality professional and not really technical.
    Let us take the expressway as an example.
    What would be vertical scaling in that example has been QUIETLY passed over by the author.
    So if increasing the number of lanes is horizontal scaling, is increasing the width of the expressway as one single large lane equivalent to vertical scaling.
    Not clear.
    Instead, I would go back to the real topic. If I increase the server -the single server RAM/ HARD DISK/ computational capacity, that is vertical scaling as I understand. And if I connect a number of similar servers in parallel, that is horizontal.

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