What is Vertical Scaling vs. Horizontal Scaling?

Scalability and Increasing Demand

Scalability is defined as how flexible a system established in the cloud is. Typically, this is applied in situations when describing if an application can accept higher traffic or lower traffic without suffering too much strain. This will severely impact how a website, web service, or application is, especially if it frequently sees user traffic that fluctuates. The more flexible a service is, the less likely it is to crash or cause widespread issues in the user experience.  The two main methods of scaling are horizontal scaling and vertical scaling.

Horizontal Scaling

Horizontal scaling provides additional nodes or computing assets to your system to better tolerate traffic. This approach is designed to add more units to process a workload and is limited by the physical capacity of servers hosted on the service. The purpose is to provide more nodes closer to some areas of the network or to offer more nodes in a particular region for users to access, or to have if any node experiences outages. In simpler terms, consider horizontal scaling as akin to increasing the number of call center employees to handle more calls simultaneously, rather than expecting a single employee to handle all the increased load.

Advantages

• Generally speaking, horizontal scaling is more accessible from the perspective of just adding hardware. The process only requires the addition of new machines and doesn’t involve analyzing system requirements needed for the upgrade.
• Scaling horizontally will less often result in extended periods of downtime. Because you will only add or remove machines, turning any working machines off while making changes won’t be necessary.
• This process has better fault tolerance. Relying on fewer nodes means storing data in fewer locations. If there are more instances, then there is less chance of losing everything in a single system outage.
• Having more machines will result in fewer performance issues overall in the long term. More endpoints in a network will result in fewer congestion issues. 

Disadvantages

• Having more machines active means more instances to run and tend to. Using multiple servers also requires load balancing and virtualization software to help distribute the workload evenly across the board. Multiple instances can also run the risk of poor internal communication and desynchronization.
• Buying more assets comes with a hefty price tag. It can be more expensive than just upgrading existing servers instead.

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Use Cases

Whether it is once per year or a constant problem bombarding business operations, scaling horizontally should be considered. Despite its shortcomings, horizontal scaling is optimal for providing good performance for services that are dependent on a stable connection to the end user. Depending on how much traffic the service usually gets, this can result in very efficient price performance. Using proper microservices, performance can remain stable across all instances with careful planning.

More machines are also suitable for avoiding outages and how catastrophic they can be. If servers are more evenly distributed across global regions, end-users will receive both better performance and a reduced likelihood of one damaged node preventing access to the service entirely. With other instances capable of alleviating the burden of traffic, updates and upgrades can come more readily.

Vertical Scaling

Horizontal scaling provides additional nodes or computing assets to your system to better tolerate traffic. This approach is designed to add more units to process a workload and is limited by the physical capacity of servers hosted on the service. The purpose is to provide more nodes closer to some areas of the network or to offer more nodes in a particular region for users to access, or to have if any node experiences outages. In simpler terms, consider horizontal scaling as akin to increasing the number of call center employees to handle more calls simultaneously, rather than expecting a single employee to handle all the increased load.

Advantages

• Vertical scaling is reasonably cost-effective in the long term. The cost is comparatively low since the service providers merely upgrade existing nodes instead of buying new units. Maintenance will remain otherwise the same once the unit is back online with the replaced components. With no new units brought online, there’s no need to make backups or implement virtualization software.
• Offers a simpler management scenario by upgrading existing hardware’s capabilities. While avoiding the complexities associated with networked instances, it is essential to consider the limitations inherent in this approach.
• Unless there are several nodes being upgraded, there is typically less need to synchronize communication between nodes. Similarly, software upgrades are less likely to happen as a result.
• Maintenance costs would be cheaper than horizontal scaling because there are fewer nodes to upkeep.

Disadvantages

• The risks imposed by downtime are significantly higher. With fewer nodes at play, having one or two units down for maintenance could spell disaster since there are fewer nodes that could work as backups.
• Similarly, having fewer nodes risks losing all your data. If all your important data is being kept on a single server, losing that server could cost all the information kept on it.
• You can only upgrade the hardware so much. There are physical limitations to what CPU is implemented or how much RAM, storage, and processing power is on a single node. If you focus exclusively on upgrading vertically, expanding horizontally will eventually become the only option.

Use Cases

This topic must be discussed with the group’s engineers and any involved stakeholders. All parties need to plan what CPUs and memory would be beneficial and how it would be possible to deliver on the price performance for such an upgrade. Regardless of the risks, vertical scaling excels at tolerating much more sporadic traffic and is worth considering if the users are relatively new to the cloud. If redundancy is not a concern, additional upgrades are far and few between, and vertical scaling will be sufficient. Though it is recommended against legacy apps that don’t require distribution or scalability, they will benefit from vertical scaling.

Vertical scaling excels in managing sporadic traffic patterns and can be a valuable choice, especially for users who are new to cloud environments. It is particularly beneficial when redundancy is not a primary concern and upgrades are infrequent. However, it is essential to note that vertical scaling is not always the ideal solution for legacy applications that do not require distribution or scalability. These applications, which may not parallelize well or have architectural constraints limiting their efficiency across multiple machines, can significantly benefit from vertical scaling. By considering the computational power requirements and scalability limitations of the workload, organizations can make an informed decision on whether vertical scaling is the most suitable approach for their specific needs.

Determining the Best Path

Cost can often play a crucial role in deciding between different scaling options. While you may have specific goals or requirements for your organization, ultimately, the cost associated with each option may heavily influence your decision-making process.

For example, while horizontal scaling may seem like the ideal solution from a functional perspective, the financial resources required for implementation could be a determining factor. Your current budget may not allow such a scaling strategy, leading you to explore other alternatives. In such situations, it’s essential to consider all available options beyond just on-premise vertical and horizontal scaling. Migrating your infrastructure to a cloud service provider, for instance, could provide a cost-effective solution that also simplifies the scaling process.

To accurately assess the cost implications of different scaling options, you might consider utilizing a cloud cost management platform. This tool can help you evaluate and compare the expenses associated with on-premise scaling versus cloud solutions, allowing you to make an informed decision based on both current and future expenditure projections. By thoroughly analyzing the financial aspects of each option, you can determine which approach aligns best with your budget constraints and long-term financial objectives.

Using either method of scaling needs to be carefully evaluated before dedicating. Especially if the application is experiencing moments of high traffic and is subsequently suffering from it, either action should be considered for the health and wellbeing of the service. That is not to say either should be considered exclusively and that it isn’t possible to accomplish a mix of both.