What do these errors mean?
Many of the errors will be HTTP status codes which can easily be looked up on wikipedia or RFC 7231. Some of the errors you encounter will not have an HTTP status code. These errors are defined by LoadStorm.
Common HTTP Status Codes
- 400: Bad Request – A VUser sent a request that is not properly formatted.
- 401: Unauthorized – A VUser failed authentication to access the target server.
- 403: Forbidden – A VUser lacked the permission to get a resource.
- 404: Not Found – Usually the link is invalid due to a typo, stale token, or the file does not exist.
- 500: Internal Server Error – Usually indicates the target server is having trouble with the load or something is wrong with the request.
- 502: Bad Gateway – Could be a configuration issue with target server.
- 503: Service Unavailable – Your server is barely functioning, and can only respond with this status code.
Common LoadStorm Error Codes
- Request Read Timeout – The request may have begun to respond but was cancelled when it reached the customizable timeout limit.
- Request Connection Timed Out – A VUser couldn’t establish a TCP connection to the target server after 10 seconds, and this limit is not adjustable.
- Socket Connection Reset – The connection was reset by the target server via a TCP reset packet which breaks the connection immediately.
- SSL Handshake Failure – The request was cancelled because it was unable to establish a secure connection possibly due to an obsolete cipher suite or mismatched SNI.
What does “response time” mean?
LoadStorm calculates the response time in the following manner:
The total time taken between the first byte of the request sent and the last byte of the response received for all requests made. This includes the network latency and the time for the server to respond.
It is also important to note that LoadStorm’s servers probably have faster internet connections than many homes and offices.
How does it generate HTTP traffic against my web application?
LoadStorm is a truly distributed application that leverages the power of Amazon Web Services to scale on demand with processing power and bandwidth as needed to test the largest web projects. As you crank up the testing load from 200 to 1,000,000 virtual users, LoadStorm is automatically adding machines for you (as many as necessary) from Amazon’s data centers to handle the processing. When your tests are done and the extra machines are not needed, they are turned off to wait for another test.
A script is processed as a sequential series of pages that you have defined in the recording. Once a page finishes, the VUser pauses for the specified time (between Min & Max “Think Time” in the script), then the next page proceeds. After the last page completes, the VUser context (session, cache, cookies) is cleared and the script starts from the beginning again with the same VUser. This same VUser will use different data upon script repeat if a CSV of User Data or dynamic response text has been parameterized within the script. As the concurrent users scale up they each begin the script for the first time, and also repeat the script after each completion.
You define the number of concurrent users you want at the start and peak of the test. You can also define a ramp down period to see how well your system recovers as the traffic subsides.
Scripts are repeated until the test is done as defined by the test duration field (in minutes) from when you began the load test.
- How do I stop a test that has killed my server?
Why does the Summary Table of test results show my missing JPGs in the HTML row?
If one of your web pages contains a reference to an image that is not available on your system, then a response header will be sent to LoadStorm with Status Code = 404. Additionally, your web server will send an HTML page indicating the 404 “Not Found” page to alert the user. That’s standard practice in web applications.
The reason LoadStorm reports the 404 errors as HTML is because your web server is sending our system the Content Type = “HTML” attribute. LoadStorm separates the data by the Content Type.
Why aren’t the 500 users evenly distributed across all 5 of my servers behind a round robin load balancer?
A round robin load balancer will not work very well for testing your configuration unless you are using a much higher number of virtual users (at least 1000 or more). Each of our simulation servers will resolve the DNS name independently of the others, but each of our servers will simulate hundreds of users. I would expect a peak load of 500 users to get routed to more than one of your servers, but probably not all 5 of them. A peak load of 200 users or less is likely to hit only one of your servers.
Will the load test show up in the Google Analytics reports? How is testing typically tracked by Google Analytics?
Most of our clients use a different mechanism for watching the user activity of a load test. There are many tools for monitoring the website, including several excellent options for open source and commercial products such as New Relic, Loggly, and Hyperic. Most of these are very inexpensive or free, up to a certain level. These types of tools provide significant information regarding the user activity as well as important data on your architecture. For example, is your web server memory bound when response times start to increase drastically? Or did your database server hit 99% utilization when throughput drops?
New Relic and Hyperic can monitor server activity from the local server using an agent. Loggly is a tool that has teamed up with New Relic for analyzing server logs which can make your life easier when trying to extrapolate the user activity from your server log.
How much does LoadStorm emulate the caching abilities of a real browser client? Will cache be reset across various sessions?
The short answer is: If your browser caches it, LoadStorm will cache it for a virtual user. When a virtual user completes a script it closes the session. Then it clears all cookies and cache before repeating the script.
Our load testing tool is designed to closely mimic the browser, but it offers three settings for caching behavior. There are a few exceptions. We do not cache HTML resources since these are often dynamically generated.
What’s the difference between “Concurrent Users”, “Sessions”, and “Total Users”?
The starting and peak number of virtual users in LoadStorm represent concurrent users or the number of simulated users at a particular point in time. Each concurrent user will last for the duration of the script. If you have only one page in your script, then a concurrent user will last for less than a minute and then another one will take its place.
For example, if you have a test with one script having one page, starting at 10 concurrent users and peak of 10 concurrent users for 20 minutes, there will be 200-300 total users simulated (and same number of sessions). LoadStorm will create a new session for each virtual user, but it will not maintain the session after the script has ended, so your session should time out as you have configured it.
The LoadStorm test parameters simulate “concurrent” users not total users. The total simulated users will generally be much higher than concurrent users, but the actual count depends on lots of other factors such as the number of pages in the script, think times, etc.
While I am running a load test and X number of users are hitting my web app, does this mean every second X number of requests are being sent to my application?
The short answer is no. LoadStorm reporting graphs include a metric called Requests Per Second, and that is what you are describing.
A virtual or simulated user does what a “real” user does as specified by the scripts and pages that you have created in LoadStorm. If there are X number of users, then there are X script instances running at that particular time.
For a nice visual of how this works see the Waterfall tab within your script: