Is something wrong with your API? Perhaps you’ve been testing it in the wrong place
An API load tester may show stable performance, but if the testing environment is chosen incorrectly, real users will see a very different picture. Cloud-based load testing is convenient when you need to evaluate an API in a real traffic environment. But if the application interface is tightly tied to back-end infrastructure, on-prem load testing can give more accurate results.
Fact: 80% of API problems are detected only under high load. Now the question is — where do you test your application interfaces for robustness?
In a cozy on-prem environment where everything is predictable but not at all like the real world? Or in the cloud, where scenarios are closer to reality, but exams can be incomplete?
Right now, the API world lives in the cloud. Well, at least it seems that way. Cloud-based load validating is trendy, convenient, and allows you to quickly load APIs from all over the world. But if your integration layer is heavily tied to infrastructure, local on-prem exams may be more useful.
So which to choose? Or maybe don’t choose at all?
If you don’t decide the right test environment, you risk seeing “stability” where there is none and getting failures where there shouldn’t be.
Let’s understand how to choose between Cloud and On-Prem, what mistakes can lurk in only one of these options and why in most cases it is better not to choose one of them, but to combine both, share insights from their PFLB experts. And let them tell you right off the bat — the answer is more complicated than “take the hybrid.” Although, yes, hybrid is almost always the best strategy.
Cloud vs. On-Prem: What are Testing Anyway?
Actually, the question is not so much about the evaluating environment, but what exactly we want to exam.
APIs are not just code. It’s also a server, network, balancers, databases, caches… And each of these elements can become a bottleneck. To dig deeper into this and understand the common vulnerabilities in application interfaces and how to address them, ResearchGate shares very insightful a practical guide for enhancing integration layer security and optimizing performance.
The classic mistake: “our API is fast.”
Okay. Question: where does it run fast? If you’re examining the API on a local network, you get perfect numbers. But users aren’t sitting in your data center.
In cloud tests, the API is under load from all over the world. That’s where the real problems immediately pop up:
- High latency in some regions.
- Bottlenecks in CDN or traffic balancing.
- Unforeseen timeouts with a large number of simultaneous connections.
On-prem tests, on the other hand, validating APIs under fully controlled conditions. This means that you can pick out exactly the bugs of the infrastructure:
- Bandwidth limitations within the network.
- Problems with database response speed.
- Performance dependency on specific server configurations.
So both options are necessary. But if you have to choose, it depends on the tasks at hand:
| Task | Cloud-based Load | On-Prem Load |
| Test the API in real traffic conditions | ✔ Yes | ✖ No |
| Track problems within the infrastructure | ✖ No | ✔ Yes |
| Test the API without the influence of external factors | ✖ No | ✔ Yes |
| Reproduce global load scenarios | ✔ Yes | ✖ No |
- If your API works globally — validate in the cloud.
- If your API depends on internal infrastructure — do it locally.
- If both points are important — it’s time to talk about hybrid examining.
But regardless of the choice, the quality of validations will depend on the API load tester you use. A good tool should support flexibility and adaptation to different load scenarios.
Business and API: what does a company lose if tests are inadequate?
There are lies, there are statistics, and there are results of incorrect Application Interface Load Testing, on the basis of which expensive decisions are made.
Here’s what can happen if you choose the wrong assessment environment:
Mistake #1. The company validated the API on a local server. They went into production — all requests suddenly took 3–5 seconds on Asian clients. Why? Local exams did not take network latency into account.
Mistake #2. Another company did all the exams in the cloud. The application interface worked perfectly. But when the traffic went to production, it turned out that their database was overloaded and scaling didn’t save them. Why?
The validations didn’t simulate the real load on the infrastructure.
The conclusion is simple: API testing affects the business directly. If it’s wrong, the company can:
- Lose users if the API slows down in prod.
- Spend millions on pointless scaling.
- Miss critical bugs that will show up on real customers.
The solution? Use an API load tester that adapts to your scenarios and allows you to combine on-prem and cloud-based exams.
API Load Validating Maturity Model: How do you figure out what you need?
Here’s what the PFLB experts suggest: instead of the boring “pick what you like”. Let’s look at API validating as a maturity process by Medium.
How does the need for testing change as the API evolves?
| Validating Stage | Description | Pros | Cons | Estimated Load Capacity |
| Stage 1: Local Testing | Manual examination of initial API functionality | Fast, easy setup | Useless for real loads | 1-10 requests/sec |
| Stage 2: On-Prem Load Testing | Internal validation under controlled load | Full control, detailed metrics | No real traffic simulation | 100-1,000 requests/sec |
| Stage 3: Cloud-Based Load Testing | Simulating global API usage | Tests real-world scenarios | Can give false positives if infra is ignored | 1,000-100,000 requests/sec |
| Stage 4: Hybrid Testing | Combining cloud and on-prem examining | Ideal balance of real & infra testing | Requires careful planning | 10,000-1M+ requests/sec |
Conclusion? Not an obvious one
You could just say, “Use the hybrid approach, it’s the best.” But that would be too simple.
In reality, it’s all about resources. Testing in the cloud costs money. Local tests take time. Hybrid approach requires good automation.
- If your API is young, you can start with on-prem exams.
- If your API is already in production, but not heavily loaded — cloud-based tests will show its weaknesses.
- If your API is critical (fintech, healthcare, SaaS) — it is better not to risk without hybrid testing.
But in any case, a high-quality Application Interface load tester will help you avoid problems and find an optimal balance between cloud and on-prem testing.