In my previous post I wrote about why it can be useful to combine running load tests in combination with functional automated tests (checks). In this post I will go in a bit deeper and give some ways to combine the two effectively and efficiently. 
2 ways to combine JMeter and WebDriver effectively
The two ways to combine Jmeter and WebDriver I will describe differ quite a bit. Depending on your situation you may want to choose one or the other for your purposes. Keep in mind, these are ideas of how I have used the two effectively together, this is not necessarily the best way for you!
Existing webdriver tests
Quite a lot of organisations already have a fairly solid base of testautomation in place, in various states of success. A relatively easy way to get performance metrics for your application is to add a timer to your existing webdriver automation scripts. For every (relevant and useful) action in the browser, you can add a start and done timer, resulting in the actual wait-time within the browser. This timer can be in an “always on” state within your automation suite. It will generate quite some data, which is not a bad thing. When you keep track of your metrics over the course of a complete cycle, for example throughout a sprint, these metrics will help give you and your team insights into possible performance regression.
Performance regression over several releases – Image linked from devel.kostdoktorn.se
While this will give you valuable information, it does not yet give you hard data of how the application runs when put under stress. In order to do that, you will have to create a separate load suite. The load suite will need to contain functional tests, similar to the ones you are running during regular (automated) regression. This way you are certain you are putting your business logic under stress and thus may slow the application down significantly. If your test environment is representative enough, or if you actually benchmarked it beforehand, you can add the Jmeter script to your automated run at planned intervals to start building up load on the server prior to the start of the full browser automated test run. Otherwise on a representative environment you can run the JMeter scripts to generate load, once the target load is reached, you can start your regular automated functional tests,
Advantages
The main advantage is that you are actively encouraged to reuse your existing automated tests. The tests under load are easily compared to the benchmark you make on a daily basis without load.
Challenges
Unfortunately there is no easyway to get to unified reporting other than to generate a set of CSV files and merge those.
Stand-alone performance measurement
As a consultant I also often end up in an organisation where there is no functional automation to reuse for a performance test. In this case I use a fully JMeter based solution for executing the performancetest, Both load generation as well as page-load times (e.g. browser rendering included) are run from JMeter. 
In order to run browser-based tests from JMeter I use the wonderful work of the people over at Jmeter-Plugins. They have created a host of wonderful plugins, but for this particular purpose I am very fond of their WebDriver Set.
The WebDriver plugins in JMeter allow you to write JavaScript testscenarios in Jmeter, which actually use the browser. This combined with the regular load tests from within Jmeter make for a strong performancetest.
Advantages
With this solution you achieve a very easy and quick way to get one unified reporting, from within the toolset showing the performance of your application, both the server response times as well as the browser response times.
Challenges
If you already have a testautomation suite running as well, taking this road implies setting up a second testsuite specifically tailored for performancetesting. The lack of reuse of existing tests makes this quite often the more expensive way of performance testing.
Technical Software Testing 