Apache JMeter is a graphical and open source tool used to load test a server's performance. JMeter is completely written in Java, so it is compatible with all operating systems that have Java installed. JMeter has a complete set of extensive tools for every kind of load testing, from static content to dynamic resources and web services.

Its installation is simple. We need to download it from the JMeter website and then just run the application. As mentioned before, it will require Java to be installed on the machine.

When we run the application at first, we will see the following window:

To run any kind of test, you need to first create a test plan. A test plan has all the components required to execute this test. By default, JMeter has a test plan called Test Plan. Let's name it to our own plan, Packt Publisher Test Plan, as shown in the following screenshot:

Now, save the test plan, and JMeter we will create a .jmx file. Save it in an appropriate place.

The next step is to add a thread group. A thread group defines some basic properties for the test plan, which can be common among all types of tests. To add a thread group, right-click on the plan in the left panel, then navigate to Add | Threads (Users) | Thread Group. The following window will be displayed:

The thread group has the following important properties:

Now, we will need to add the HTTP request defaults. Right-click on Packt Thread Group and then go to Add | Config Element | HTTP Request Defaults. A window similar to the following will appear:

In the preceding window, we have to just enter the URL of the application or the IP address. If the web server uses cookies, we can add HTTP Cookie Manager too, in which we can add user-defined cookies with all the data, such as the name, value, domain, path, and so on.

Next, we will add an HTTP request by right-clicking and navigating to Packt Thread Group | Add | Sampler | HTTP Request, and the following window will appear:

The important field here is Path. We want to run the test only against the home page, so for this HTTP request, we will just add a slash (/) in the Path field. If we want to test another path, such as "Contact us", we will need to add another HTTP request sampler, as in the preceding screenshot. Then, in the path, we will add path/contact-us.

The HTTP Request sampler can be used to test forms too, where POST requests can be sent to the URL by selecting the POST method in the Method field. Also, file upload can be simulated.

The next step is to add some listeners. Listeners provide some powerful views to display results. The results can be displayed in a table view and different kinds of graphs can be saved in a file. For this thread group, we will add three listeners: View Results in Table, Response Time Graph, and Graph Results. Each listener view displays a different kind of data. Add all the preceding listeners by right-clicking on Packt Thread Group and then navigating to Add | Listeners. We will have a complete list of all the available listeners. Add all the three listeners one by one. Our final Packt Publisher Test Plan panel on the left-hand side of JMeter will look similar to the following:

Now, we are ready to run our test plan by clicking on the Start button in the upper tool bar, as shown in the following screenshot:

As soon as we click on the Start button (the green arrow pointing to the right-hand side), JMeter will start our test plan. Now, if we click on the View Results in Table listener on the left panel, we will see data for each request in a table, as shown in the following screenshot:

The preceding screenshot shows some interesting data, such as sample time, status, bytes, and latency.

Sample time is the number of milliseconds in which the server served the complete request. Status is the status of the request. It can be either a success, warning, or error. Bytes is the number of bytes received for the request. Latency is the number of milliseconds in which JMeter received the initial response from the server.

Now, if we click on Response Time Graph, we will see a visual graph for the response time, which is similar to the one that follows:

Now, if we click on Graph Results, we will see the response time data along with graphs for average, median, deviation, and throughput graphs, as shown in the following graph:

Apache JMeter provides very powerful tools to load test our web servers by simulating users. It can provide us with data regarding the amount of load that makes our web server's response slow, and using this data, we can optimize our web server and application.