How do you define and conduct tests to check system resilience under high load?

To test the system's stability under high load, I conduct load testing that includes the following steps:

1. Defining testing goals: which metrics are important — response time, throughput, resilience to peak loads.
2. Preparing the test environment: as close as possible to the production environment, with necessary services and data.
3. Creating load scenarios: modeling real user actions with increasing numbers of simultaneous requests.
4. Using tools: such as JMeter, Gatling, or custom scripts for load generation.
5. Monitoring the system: tracking CPU, memory, network usage, response times.
6. Analyzing results: identifying bottlenecks, failure points, performance degradation.
7. Optimizing and retesting: making changes and checking their effectiveness.

Example: for a web application, I ran tests with a gradual increase in users from 100 to 10,000, recording response times and error counts. This helped identify the need for database optimization and caching.