Load Testing vs. Stress Testing: What’s the Difference?

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Both load testing and stress testing are types of software performance testing. It’s easy to confuse them because their ultimate goal is the same. Namely, to identify weak spots of your system that you are testing and help you eliminate or upgrade them until they can become advantages of your system.

Using only one of them might not be enough. Their different approaches will allow you to achieve significant insights about distinct yet equally important aspects of your system’s capability.

The more you know about your system’s weaknesses, the better you can prepare to eliminate them or to deal with any outcome they might cause.

How to Use each of them, and what Advantages do they Bring?

How does Load Testing Work?

You can perform load testing either manually or automatically. In both cases, you enlarge the workload in your system to the point where your system has to deal with bigger traffic than it normally does.

The test consists of sending a multitude of requests to the target and receiving responses from it. These requests must resemble the ones that would come from real users as much as possible. After all, you are testing what levels of traffic from real users your system will withstand. 

That allows observing how well your system functions under this workload. If you notice your system is struggling, you can identify its causes and fix them. A single performance weak spot might compromise the overall performance.

Because of a great number of requests that you need to complete the test, performing it manually is not a productive or efficient way of getting things done. By using tools that let you complete the test automatically, you will increase the numbers and save up lots of time.

What do you need it for?

Load testing, like any other test, should expose every possible failure of your system before its launch. It’s like a rehearsal before the premiere.

For instance, if you are planning to run a new ad campaign that will result in significantly increased traffic on your site or in any other application, you will not regret testing how well your system would withhold such a workload.

If you forecast the traffic on your system to be bigger than it has ever been, your system might crash. You need to make sure it will not happen. Otherwise, it would only worsen your reputation. All your investment in advertising would just be flushed down the drain.

You can make use of it even after your system has been launched if you want to test it against upcoming changes or new updates.

The Main Metrics

Load testing is meant for assessing the following:

  • Scalability

It’s the ability to sustain the complete functionality of your system under changing circumstances when the scale of tasks in the system significantly expands or boils down to random sequences.

  • Performance

The pace at which different tasks are completed in the system while dealing with a respective load and how the changes of the latter affect the pace. It’s the average response time for requests.

  • Stability

The memory and CPU usage and how it changes depending on the load.

  • Reliability

It measures the number of errors that occur depending on the load level. Usually, the possibility of errors increases along with a bigger load.

Each of these metrics can provide valuable information that helps to draw conclusions on which improvements can be made.

How does stress testing differ?

Stress testing goes way further and extends the load testing to the extreme. It tests not how well the system will do under a certain load but rather examines the maximum load that a system can endure before crashing.

That is the goal of stress testing. However, its means is actually crashing the system. The idea is to identify the breaking point after which the system starts deteriorating.

It works by constantly increasing the load far exceeding the system’s normal capacity, and it goes further until it breaks and becomes incapable of functioning any longer.

Recognizing the limits of the system allows one to temper expectations of the system’s performance and work on its improvements. If the traffic is growing and approaching the breaking point, it can be pushed further with new developments, thus avoiding a risky crash that would result in dissatisfaction among the users.

While load testing might be sufficient for normal usage of the system to be assessed and improved, evaluations under extreme conditions might be of use as well. Or even more important when it seems that reaching such extremes with real traffic is more probable.

Proxies – Where the Difference Ends

Since both load testing and stress testing simulate the traffic that must prepare your system for the real traffic, this simulation must be similar to the real traffic. The latter consists of different users that come from different places with distinct IP addresses.

Proxy servers are known for their ability to hide an IP address and provide substitutes that can be constantly rotated. Their main objective is to make their users seem like multiple different internet users.

This feature serves equally well for the discussed types of software testing. Since you need to test how well your system works for different setups and operating systems, there’s no better way of doing that than by employing different IP addresses from separate devices that have all these differences.

Proxies let you send unlimited connection requests simultaneously without having any inner link with one another. It makes them seem like they are coming from different users.

Residential proxies use IPs of actual internet users with different devices. By employing their IPs, proxies can make your traffic genuine. That enables more preciseness in the testing process that can produce more useful results.


The main difference between load testing and stress testing is that the former examines the system under a plausible workload while the latter test it under extreme conditions that can or do break it. However, they both need to simulate genuine traffic to test the load, and proxies are the best solution to achieve that.

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