Today I received a report of a bug in how the Opera.com startup page was presented to some browsers. In particular, people with Brazilian language.
This was traced down to being a bug in the accept-language.vcl extension that we are using on both My Opera and Opera.com.
In particular, the bug had to do with static buffers being reused and overwritten during the
Accept-Language string parsing, essentially due to my non-optimal C skills :) Now this bug is fixed and new test cases were added, so to hopefully avoid regressions in the future.
So now clients with Accept-Language containing strings like
zh-CN, etc… will be correctly recognized by the VCL code, and they will get the correct page served by varnish.
As always, thanks to Opera, the code is freely available, and I have to say it's not really experimental dangerous stuff anymore. It's been quite proven in the last few months (these few bugs excluded). At least your Varnish server shouldn't explode :-) Have fun!
I have been working on setting up and troubleshooting Varnish installations quite a bit lately. After deploying Varnish on My Opera for many different uses, namely APIs, avatars, user pictures and the frontpage, we also decided to try using Varnish on www.opera.com.
While "www" might seem much simpler than My Opera, it has its own challenges.
It doesn't have logged in users, or user-generated content, but, as with My Opera, a single URL is used to generate many (slightly) different versions of the content. Think about older versions of Opera, or maybe newest (betas, 10.50), mobile browsers, Opera Mini, site in "Mobile view", different languages, etc…
That makes caching with Varnish tricky, because you have to consider all of these variables, and instruct Varnish to cache each of these variations separately. No doubt
opera.com in this respect is even more difficult than My Opera.
So, we decided to:
- cache only the most trafficked pages (for now only the Opera startup page)
- cache them only for Opera 10.x browsers
- differentiate caching by specific version (the "x" in 10.x)
We basically used the same Varnish config as My Opera, with the accept-language hack, changing only the URL-specific logic. With this setup, we managed to cut down around 15% of backend requests on