For apache, exists the Apache Bench (ab) tool. This tool helps you measuring the performance of HTTP servers in a Linux environment, it works by generating a flood of requests (DoS kinda if your server isn't properly configured the amount of simultaneous requests ...) to a given URL and returns some easily digestible performance related metrics to the screen. This simplicity makes it appealing for running quick and dirty load tests, and a nice benefit to uncovering limits in your web stack or a service bottleneck that you did not anticipate. It is designed to give you an impression of how your current Apache installation performs. This especially shows you how many requests per second your Apache installation is capable of serving. This tool helps you to basically know:
- When will my application break (with how many users)?
- What's your application average response time at a huge amount of simultaneous requests.
- What is the maximum number of requests-per-second that my server can handle?