Bandwidth Limited Websites

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What’s holding you back?

When you hit the limits of how much load your website can handle, you almost always want to know what’s holding you back. You already know you’ve reached the limit, but what part needs to be changed to go higher?

The more load a website gets, the more resources it’s going to consume. One of the many types of resources the server needs to function will run out before the others. Sure, an extremely well balanced server setup will run out of all types of resources at the same time, but that’s probably not very common. To figure out what resource type is causing the bottleneck, you’ll need to look at different things. Load Impact offers several interesting performance metrics that will reveal what’s holding you back. Then surely, as soon as you fix that, the next bottleneck will become visible, but that’s another blog post.

In this post, we’ll share some information about how you can determine your web site performance is held back by bandwidth issues and a bit about what you can do to solve it.

How do I know it’s the bandwith?

Depending on where you host your website, you may have access to tools and graphs from the hosting company that provide you with valuable information. But assuming that you don’t have that tool available, let’s look at how you can use Load Impact to tell you what you need to know.

We’ve created a very simple website that is very bandwidth limited. This website contains a single .html file, absolutely no Python, PHP, Java, Perl or anything similar involved at all. The one file is called heavy.html and contains roughly 16Mb of the letter “A.” When many concurrent user request heavy.html, a lot of bits will have to leave the web server all at the same time. This is the graph from the test:


This graph reveals two interesting things. First of all, if you didn’t know already, you can add more than two standard data series to your Load Impact graphs. By default, Load Impact will give you a number of active clients and an average response time. In this case, I’ve added the Bandwidth data series to the graph.

Secondly, the bandwidth graph pinpoints exactly what we were hoping for. The bandwidth usage actually hits a plateau at roughly 70 Mbit/s. This means that somewhere between the software on my test server and the software on the measuring probe, there is a bandwidth limitation of about 70 Mbit/s. It’s important to point out this result doesn’t point out the exact location of that bottleneck, it just tells you it’s there. To make sure you have a bottleneck in your hosting environment, you should run the same test from different test servers. Load Impact currently offers 8 different load zones, each load zone is in a different geographic location. Make sure you run tests from different load zones, or even more interesting, you can add 4-5 load zones into the same test. If you can still see your plateau at the same bandwidth usage, you can be fairly sure that you’ve found your limit.

Don’t worry if you’ve already run a series of tests using Load Impact and didn’t add bandwidth to the graph. The data is still stored on our servers and you can add bandwidth when looking at older tests as well. So you might already have interesting data to analyze.

Ok, so what do I do about it?

If you are held back by bandwidth limitation, the next step is obviously to try and do something about it. There are many potential ways you can bring down the bandwidth need.

Use compression

Make sure you use compression like gzip or deflate. By compressing the content before it’s sent from the server to the browser, you pay with some CPU resources to gain a little bandwidth. It’s safe to enable this as the server will only send compressed content if the browser says it can handle it. Check if your website uses compression in the developer tools. Open the Network tab in the developer tools, refresh your browser window to get content, and select the website URL.


Check for the Content-Encoding header in the response:

Minify things

By removing white space from all static content such as javascript and css files, you can gain some bandwidth. Minifying is most often done in your web application software, so how to do it depends on what type of Web application you are running. Read more about minifying here:

Reduce image quality

It may sound backwards, but a lot of websites are sending images to the browser in 300 DPI, that’s great if the user want’s to print the image, but most images are just displayed on the actual web site where 72-96 DPI is sufficient. A good text about the why and how is found here

Have your cache settings correct

In a test such as the one in this post, we didn’t want caching to happen because we wanted to illustrate something. If caching had been enabled, response headers in the image above would’ve included an ‘Expires’ header. In real life, you probably want your web server to instruct the browser to cache all static content. Correctly configured caching entails that the browser won’t download the same logo-type, javascript and css files etc. every single time a web page is downloaded from your server.
Google has written a bit about caching as part of their PageSpeed Rules.

Use a CDN

A method that actually covers a lot of the above tips all in one is to use a content delivery network (CDN). A CDN provider will store your static content on their servers and serve it for you. You can check the bandwidth of each CDN. Unless you are one of the bigger Internet companies, chances are that the CDN provider will have more bandwidth available. They almost always have more than one physical location, so that a user from Spain gets the content from a server in or near Spain while a UK user gets his content from a server in the UK. The end result is that the user gets his content faster and your server never have to see the traffic. The better CDN providers can also do some of the things like minifying of even image quality reduction automatically for you. So chances are that you end up saving both time and bandwidth.

One of Load Impact’s great friends in the industry is MaxCDN. They’re a trusted company in the space, and we’d recommend you take a look at them first when CDN shopping!

That’s it

Opinions? Questions? Tell us what you want think in the comments below.


    So interesting and actual! Thank you very much for descovering this theme.

  • Eugene


    I’m just starting with LoadImpact. I can’t find the option of showing the bandwidth graph. Where is it located?


    • Eugene

      Allright, you can remove my comment. I found it already!

      • chrisloadimpact

        Glad you found it Eugene! Let us know if you need any more help :)

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