Monthly Archives: September 2015

Performance testing with Gatling – record and playback

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Post summary: How to record a simulation with Gatling recorder and play it back.

Current post is part of Performance testing with Gatling series in which Gatling performance testing tool is explained in details.

Run the recorder

Once Gatling is downloaded recorder can be run with “GATLING_HOME\bin\recorder.bat”. The recorder has two working modes: HTTP Proxy and HAR Converter.


Configure browser proxy

Network traffic should be redirected through Gatling Recorder in order to be captured in HTTP Proxy mode. By default, recorder works on 8000 port, but this is configurable. If a web application is being tested then the browser should be configured to work through the Gatling Recorder proxy. Firefox is configured from Tools -> Options -> Advanced -> Network -> Settings… -> Manual proxy configurations: -> localhost with Port: 8000, Use this proxy server for all protocols.


Microsoft Edge browser has also specific configurations for setting a proxy: Settings -> Network & Internet -> Proxy -> Manual proxy setup.


Configure system proxy

If network traffic that is going to be recorded is not browser-based, e.g. REST or SOAP call, then system-wide proxy should be configured. For Windows this is done through Control Panel -> Internet Options-> Connections -> LAN Settings -> Use a proxy server for your LAN. This configuration forces applications network traffic to go through a configured proxy. The same configuration is done in order to configure a proxy for Chrome, Opera and Internet Explorer browsers.

Use Gatling Recorder’s HTTP Proxy

Once a proxy is configured then “Start” button runs the Gatling Recorder proxy and opens a new window that shows all requests being captured. “Stop & Save” button stops the proxy and saves all requests that went through into a Gatling simulation file. The image below is a screenshot of recording of testing RESTful stub server built in Build a RESTful stub server with Dropwizard post which will be used for testing purposes in these tutorial series.


HTTPS and Gatling Recorder

HTTPS is HTTP over SSL or TLS security layer. It is designed to bring security in normal HTTP communication. This security is guaranteed with the server being issues certificate issued by a certification authority. Gatling is intercepting the traffic between server and client (browser) hence is considered intruder into safe HTTPS communications. There are several mechanisms provided by the recorder to handle this. Those are handled in HTTPS modes configuration. The easiest to use is “Self-signed Certificate”. In this mode Gatling is using a certificate which is not issued for web application being tested, hence browsers are recognizing it as invalid. Browsers give warning that certificate is invalid and asks for user’s permission to continue. Beware: in normal daily internet browsing such warning is a sign that something is wrong, your HTTPS connection might be sniffed, so be careful what data you provide in such cases. Some sites are configured in a manner that if the certificate is invalid you are unable to proceed. Here is how Firefox react in both cases. When there is a possibility to continue there is “Add Exception…” button.


Other options to handle certificate problem is “Provided Keystore” and “Certificate Authority” HTTPS mode. For both valid certificate should be issued for the domain under test. More details how to do this can be found Gatling Recorder page.

In case traffic that has to be captured is not browser-based tools that are used to simulate requests should provide support for handling missing valid certificates in case of “Self-signed Certificate”. If you custom code that sends SOAP is being written then Send SOAP request over HTTPS without valid certificates post describes how to work without valid certificates. This can be applied also in case of RESTful HTTPS call.

Use Gatling Recorder’s HAR Converter

Generating and handling SSL certificates could be a painful process. Before diving into it, another option, that is good to be considered is using Gatling Recorder in HAR Converter mode. In order to do this, all network traffic should be recorded as HTTP Archive – HAR. This can easily be done with Chrome DevTools plugin that is activated with F12 keyboard key. Remember to select “Preserve log” checkbox before starting to record test scenario. Once the scenario is recorded it can be exported with a right mouse click and then “Save as HAR with content”.


Beware: sensitive data such as passwords are also exported as plain text in HAR archive. Once traffic is being recorded and exported it then gets converted to Gatling simulation by Gatling Recorder. In order to exclude not important requests, e.g. images, CSS, JS, call to other domains there is Blacklist that accepts Java regular expressions. It is possible to use default list by clicking “No static resource” button. There is also Whitelist that can accept only needed requests.


Running recorded scenario

Gatling Recorder saves scenarios in the directory configured in “Output folder*”. By default it uses “GATLING_HOME\user-files\simulations” folder. Simulations are run with “GATLING_HOME\bin\gatling.bat”. Once started is looks default simulations folder and gives a list of all simulations. The user selects simulation by number in the list and then gives a short description for this run. Simulations can be changed before running in order to configure a different number of users as it is 1 by default. If simulations are recorded in different that default folder then runner cannot find them. In such case one option is to move them to “GATLING_HOME\user-files\simulations” or:

Use non-default simulations folder

In order to use differently than default simulation’s folder then this should be configured in “GATLING_HOME\conf\gatling.conf” file. Following configuration elements hierarchy: gatling -> core -> directory -> simulations = “C:\\Gatling\\simulations”.


Gatling recorder is powerful and provides various ways to record a scenario. Either by capturing network traffic in HTTP Proxy mode or by importing already captured network traffic in HAR Converter mode.

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Performance testing with Gatling

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Post summary: Tutorial how to use Gatling and do successful performance testing with it.

This is first of series of posts designed to give a complete overview of Gatling performance testing tool. Other posts in the series are:

Performance testing

Performance testing is a way to identify how an application behaves in case of high user load. In this post “performance testing” is used as a collective term but it actually has different aspects which are described in Performance, Load, Stress and Soak testing post. The essence and best practices of performance testing are described in How to do proper performance testing post. Current post is about how to do it with Gatling


Gatling is a very powerful tool. Build on top of Akka it enables thousands of virtual users on a single machine. Akka has message-driven architecture and this overrides the JVM limitation of handling many threads. Virtual users are not threads but messages. Tests are written in Scala, which makes scenarios creation and maintenance more complex.

Gatling Recorder

For easy scenario creation, Gatling provides very good recorder. It works as a proxy capturing all traffic and converting it into Gatling scenario. Detailed explanation how to record scenario can be found in Performance testing with Gatling – record and playback post.

Run simulation

Once a simulation is recorded it can be changed with proper values, user count, etc and run. How to run a simulation can be found at the end of Performance testing with Gatling – record and playback post.

Gatling terminology

“Simulation” is the actual test. It is a Scala class that extends Gatling’s io.gatling.core.scenario.Simulation class. Simulation has an HTTP Protocol object instantiated and configured with proper values as URL, request header parameters, authentication, caching, etc. Simulation has one or more “Scenario”. A scenario is a series of HTTP Requests with a different action (POST/GET) and request parameters. The scenario is the actual user execution path. It is configured with load users count and a ramp-up pattern. This is done in the Simulation’s “setUp” method. Several scenarios can form one simulation. There are other elements like Feeders that create input data and Checks that are used to validate responses. Those will be discussed in Performance testing with Gatling – recorded simulation explanation post.


REST and SOAP are also easily supported by Gatling since in they are very nature they are just HTTP requests. SOAP is HTTP POST request with XML data put into request body. It is possible to have some special HTTP Headers in the request but in general case this is it. REST is either HTTP GET request with key/value params in the URI or HTTP POST request with JSON or XML data into request body. There are also HTTP Header parameters in the request to indicate the data type being sent, etc.


Scala is object-oriented language and functional programming language, providing best of both worlds. Everything in Scala is an object, there are no primitive data types like int, long, char, etc in Java. More simple Scala tutorial can be found in Performance testing with Gatling – Scala fundamentals post.

Advanced Gatling

In order to properly edit simulation, it should be included in a project and imported in some IDE. Gatling provides a Gatling Maven plugin. There are more plugins to be used they can be found on Gatling extensions page. Simulation can be recorded with the recorder and further processed as a Maven project. Information with examples how this can be done is shown in Performance testing with Gatling – integration with Maven and Performance testing with Gatling – advanced usage posts.


Gatling is very good performance testing tool. It is capable of creating an immense amount of traffic from a single node. It requires basic knowledge in Scala which is his main disadvantage. Java code can be directly used in Scala classes. Advance usage is from a Maven project which makes it more easy to use and maintain scenarios.

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Performance, Load, Stress and Soak testing

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Post summary: Performance, Load, Stress and Soak testing are different aspects of one goal – proving that application will function correctly with a large number of users.

Previously I have written for non-functionally testing the application in conditions of a large number of users in How to do proper performance testing post. There I’m using only one term performance testing. If we have to be precise there are several different types of testing that can be done to achieve the goal of sustaining a large number of users.

Performance testing

Testing the system to find out how fast is the system. Create a benchmark of system response times and stability under particular user load. Response time should be small enough to keep users satisfied.

Load testing

Testing how the system performs when it is loaded with its expected amount of users. The load can be slightly increased to measure if and how performance degrades. Load and performance testing are tied together. System performance depends on the load applied to it. Load testing should prove that in case of expected and peak users load system performs close to benchmarks measured with a small load.

Stress testing

Testing of the system beyond its normal expected amount of users to observe its behavior. Sometimes the system is loaded until its crash. The idea behind this testing is to understand how the system handles errors and data when it is highly loaded, is data preserved correctly, what load can crash the system, what happens when the system crashes.

Soak testing

This is kind of underestimated but it is rather important. Soak testing is to test the system with expected or little more than the expected load for a long amount of time. The idea behind that is system may respond fast during short tests but actually to hide some memory leak which will become obvious after a long amount of time.

Knowledge is power

Knowing the problems helps to prepare for them. Procedures can be prepared and followed to avoid a system crash. In case there is a module identified to be slow but important for business it can be made configurable and can be turned down in case of a higher load. In case users count have reached a critical level that could endanger the system, support can reject some users. In case of memory leaks, support can restart the system at regular intervals in time of a low load to avoid a crash. All those and many more can be done only if we know the system.


There are different techniques to prove that system can handle the number of users expected by business. I like the term performance testing and use it to combine all the types of testing above. It is not that important to know the precise definition of the terms than to know what is good to be done in order to prove system can handle a large number of users or to identify the bottlenecks in case it cannot.

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