Because endpoints are URLs, you can – and should – monitor them to ensure they stay online. When talking about online services and websites, you’ll often hear the word “uptime”. This is the percentage of time your application stays up – in other words, the percentage of time your app is accessible and functioning. Outages and performance errors will lower your overall percentage.Monitoring your endpoints also gives you metrics on which endpoints are being accessed and what types of API calls developers are making. This can help you track user behavior, and gain insight into which endpoints are highly trafficked so you can maintain your performance.

That is called profiling, not performance testing. Performance testing should ensure that a piece of code runs within a desired amount of time, given a certain context, before the new code goes into production.

It is also good practice to make sure that your load testing is functionally correct. Both the performance and functional goals can be codified using thresholds and checks (like asserts).

k6 provides great primitives for code modularization, performance thresholds, and automation. These features make it an excellent choice for performance monitoring. You could run tests with a small amount of load to continuously monitor the performance of your production environment.