Tag: httpd.conf

HTTP Compression – Have you checked ALL your browsers?

Apache has been my web server of choice for more than a decade. It was one of the first things I learned to compile and manage properly on linux, so I have a great affinity for it. However, there are still a few gotchas that are out there that make me grateful that I still know my way around the httpd.conf file.

HTTP compression is something I have advocated for a long time (just Googled my name and compression – I wrote some of that stuff?) as just basic common sense.
Make Stuff Smaller. Go Faster. Cost Less Bandwidth. Lower CDN Charges. [Ok, I can’t be sure of the last one.]

But, browsers haven’t always played nice. At least up until about 2008. After then, I can be pretty safe in saying that even the most brain-damaged web and mobile browsers could handle pretty much any compressed content we threw at them.

Oh, Apache! But where were you? There is an old rule that is still out there, buried deep in the httpd.conf file that can shoot you. I actually caught it yesterday when looking at a site using IE8 and Firefox 8 measurement agents at work. Firefox was about 570K while IE was nearly 980K. Turns out that server was not compressing CSS and JS files sent to IE due to this little gem:

 BrowserMatch \bMSIE !no-gzip gzip-only-text/html

This was in response to some issues with HTTP Compression in IE 5 and early versions of IE6 – remember them? – and was appropriate then. Guess what? If you still have this buried in your Apache configuration (or any web server or hardware device that does compression for you), break out the chisels: it’s likely your httpd.conf file hasn’t been touched since the stone age.

Take. It. Out. NOW!

Your site shouldn’t see traffic from any browsers that don’t support compression (unless they’re robots and then, oh well!) so having rules that might accidentally deny compression might cause troubles. Turn the old security ACL rule around for HTTP compression:

Allow everything, then explicitly disable compression.

That should help prevent any accidents. Or higher bandwidth bills due to IE traffic.

The Complexity of Web Performance

Helping a colleague this week, we uncovered some odd behavior with a site whose performance he was analyzing. Upon first glance, it was clear that this site had a performance issue – they had HTTP persistence disabled. Immediate red flag in the areas of network overhead and geographic latency.

Further digging exposed something more sinister. It seems that HTTP persistence was only disabled for browsers with MSIE in the user-agent string. Even if the user-agent string was just MSIE, HTTP persistence was off.

The customer was very forthcoming and sent us their standard httpd.conf file. This showed no sign of the standard (and frustrating) global disabling of persistence for Internet Explorer.

Finally, it came to us. The customer had provided a simple network diagram, and there, just before packets hit the Internet, was a Layer 7 firewall. How did we know the Layer 7 firewall was the likely cause? Because this device was also the one that provided compression for the content going out to customers.

A Layer 7 firewall happily rewrites HTTP headers to reflect the nature of the compressed content (content-length or transfer-encoding: chunked) and to add the gzip flag (accept-encoding:gzip). Since this device was already doing this, it was pretty clear to us that it also had a rule that disabled HTTP persistence for anything with MSIE in the user-agent string.

This was a fine example of the complexity of the modern Web application infrastructure. In effect, there were two groups with different ideas of how Internet Explorer should be handled at the network layer, and neither of them seems to have talked to the other.

When you have a Web performance problem, indulge in a thought experiment. Create an imaginary incoming Web request and try to see if you can follow it through all the systems it touches on your system. Put it on a whiteboard, a mindmap, whatever works.

Then invite the system architects and network engineers in and get them to fill in the gaps.

No doubt that will lead to the “ah ha!” moment.┬áIf nothing else, it’s a good excuse to put pizza on the company card. But I have no doubt that you will walk away with a better understanding of your systems, which will make it easier for you to talk to all the people responsible for keeping your systems running.

TAKEAWAY: Just because the part of the Web application you work on is working fine, it may be affected by other components that are not tuned or configured for performance. Get to know the entire application at a high level.

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