What is Load Testing and Why is it Important?

January 10th, 2024 by inflectra

Software load testing is a type of performance testing where you simulate real-life user load on any software, application, or website to determine how it behaves under normal and peak conditions. It's about understanding how the system performs when multiple users access it simultaneously. This can involve simulating hundreds or thousands of users to see how the software holds up under heavy demand.

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Why Load Testing is Crucial?

The key reasons for conducting software load testing are as follows:

Capacity Planning and Scalability: Understanding the maximum capacity of your application and how much load it can handle is essential. Load testing helps in identifying the optimal point at which the application's performance starts degrading, and you can plan for scaling up resources accordingly.
Performance Optimization: It helps identify the parts of your software that degrade its performance. For example, it might uncover that a particular function slows down under heavy load. Developers can then optimize or fix these issues to ensure smoother operation.
Stability and Reliability: Ensuring that your application is stable and reliable under varying loads is vital. Load testing can help identify and rectify stability issues, preventing crashes and downtimes that could otherwise lead to a poor user experience and loss of trust.
Infrastructure Adequacy: It's essential to know if your current infrastructure is adequate to support your application. Load testing can reveal the need for better hardware, more efficient software, or a more robust network.
Cost Management: By understanding the load limits of your application, you can better plan your infrastructure needs and avoid overspending on resources that aren't necessary.
User Satisfaction: Ultimately, the goal is to ensure a smooth, responsive experience for the end-user. If your application slows down or crashes under heavy load, users are likely to be dissatisfied, which could lead to a loss of customers and revenue.

What are the Elements of Load Testing?

1) Load Testing Planning

The main elements of load testing planning are as follows:

Identify Goals
Validate Endpoints
Confirm Service Level Agreements (SLAs)

Identify Goals

The first question to answer in the planning phase is what the goals of your testing are. Is your primary interest to establish metrics for your business and technical operations through black-box testing, or more developer-focused where you're looking to understand the impact and effects on your system as you run what we call white-box tests?
For the metrics-minded: are you looking to validate performance, i.e., how fast (or slowly!) the system responds to requests? Or are you looking to validate scalability, i.e., at what levels of incoming traffic your system starts to fall behind? Or are you looking to understand how reliable your system is, i.e., after how long at known amounts of load your system starts to crumble?
For the developer: do you have enough system instrumentation and monitoring so you can derive actionable insights as your system responds to the load generated by the testing? Can you answer with certainty when and where your system hit bottlenecks or fragile architecture as it is exposed to load testing? If so, can you quantify what part of the system represents the largest degradation in serviceability, thus implying a priority of what performance bottleneck to address first?

Validate Endpoints

The next question is to clarify and understand what exactly you need to test in your plan.

Are you looking to test the responsiveness of specific pages or web services?
Are you instead looking to test broadly across all UI and API endpoints of the application?
Or are you looking for a more complex test where you have any number of micro-services interacting via or within some workflow or defined scenario?

Confirm Service Level Agreements (SLAs)

The value of load and performance testing is directly proportional to how closely your test resembles real-life or expected usage. Knowing your business demands a particular feature to support incoming throughput at 1 million r/s (requests per second, sometimes abbreviated RPS) obviously largely dictates the end goal of testing that feature. For other features where no formal SLA exists, we recommend understanding existing traffic patterns in order to derive reasonable levels of traffic and load.

Application Performance Monitoring (APM) services such as New Relic, AppDynamics and Dynatrace should be able to help you understand:

Distribution of throughput in requests per second - average, peak, etc.
Distribution of response times and resource utilization at average and peak loads.
Throughput distribution by API endpoint. This is rarely evenly distributed, more commonly one or a few endpoints representing a significant majority of all traffic with the rest spread out across a long tail.
Throughput distribution by users. Typically we see a few users or accounts generating most traffic, with the rest spread out across a long tail.
Throughput distribution by geography.

Tools & Infrastructure

Success of load testing depends on proper choice of tooling, and sufficient infrastructure. In addition, you will need to determine what sizing ratio to use between the test, staging and production environments. In an ideal world you would simply replicate production for test and staging, but that may be too expensive.

Instead you can consider scaled down environments as illustrated below:

The key is to then appropriate scale down the performance metrics as well, for example a test environment that has 10% of the resources of production should be tested with no more than ~ 10% of the load that the production environment would expect. Note that you need to be careful with this assumption as the performance scaling may not be linear.

2) Load Testing Execution

The main elements of load testing execution are as follows:

Modeling Load
Load Scenario Creation
Execution & Monitoring

Modeling Load

As you move to configure your load testing, it is important to consider the traffic pattern of your tests. Will your testing be satisfied by simple and repetitive "hammering" of specific pages or APIs? Or will you need something more dynamic and sophisticated, typically accomplished through scripting of logic and execution flows? Or will you rather want to test using true replication and replay of real-world traffic?

As you move to make your load testing more structured, define your testing of the various pages and services in composable scenarios. Consider using traffic shaping to model ramp-ups/ramp-downs, adding multiple scenarios to your test, distributing the traffic proportionally according to your understanding of endpoint distribution. Also, if your choice of load testing tooling and infrastructure supports global distribution of traffic, consider using cloud-based load generators based upon your understanding of geographic distribution of your incoming traffic.

Load Scenario Creation

We recommend composing your load tests into reusable modules or scenarios, where each scenario typically tests an individual page, API endpoint or distinct user workflow. This scenario can then be used standalone to validate serviceability of that particular page, and/or be used as one of many scenarios in a more complex configuration where performance and scalability of the overall system is looking to be characterized when used in a more real-world production setup.

Execution & Monitoring

Once you have a testing setup that models your SLAs and can satisfy your load testing goals, consider integrating execution of your tests into your existing CI/CD infrastructure and integrated into a test management tool such as SpiraTest:

Summary

In summary, software load testing is about ensuring that your application can handle its intended load with efficiency, stability, and speed, leading to a better user experience, more reliable performance, and informed infrastructure investment.