Skip to main content

Varnish, Drual and ical (.ics): expiry issue fixed

My normal configuration of a public site on my servers involves using varnish for the page cache and setting expire page to 1 day. This mostly works quite well (the varnish module in Drupal takes care of clearing the varnish cache when you're creating/editing content).

We recently launched a new Drupal version of the Calgary French & International School (okay, I was just along for the tail end to help with the launch, Karin and Rob get the credit for all the work), which includes an ical feed for parents (generated from views of course).

That's an excellent thing - parents can subscribe to the feed and have all the upcoming events on their mobile device (or google calendar, or both). But we discovered that although it works great on the Mac desktop, it wasn't working well for iOS (i.e. the iPhone). It would poll frequently enough, but only actually update once a day.

It turned out that these two devices are interpreting the http header 'cache-control' differently - on the iphone, it appeared to interpret it to say don't both looking for fresh data more than once a day. The header is not very well defined unfortunately, but it is used by Drupal/Varnish to control the maximum expiry date, so we didn't want to crank it too low (or risk a badly performing site, since most access is anonymous).

The solution was actually simple: a little help in the varnish vcl file, in my vcl_deliver function, below. The piece I added was the second if, and it's just modifying the cache-control header on output if it's delivering a file with extension 'ics'.

sub vcl_deliver {
  if (resp.http.magicmarker) {
    unset resp.http.magicmarker;
    set resp.http.age = "0";
  }
  if (req.url ~ "\.ics$") {
    set resp.http.cache-control = "public, max-age=60";
  }
}



Popular posts from this blog

What to do in the age of Trump?

Well, that's the question of the day. If you're part of an organization that does advocacy work, rather than waiting to see what happens first, might as well get yourself ready, even if the details are sketchy still. Here's one opportunity that's ready for you now, message courtesy of Steve Anderson of OpenMedia.

OpenMedia, David Suzuki Foundation, SumOfUs and a range of other organizations are supporting a new shared set of civic engagement tools.

Vancity Community Foundation is providing some support to subsidize some of the cost of the tools to select values-aligned organizations that sign up before February 28th.

Interested? You can learn more or book a demo from here: http://tools.newmode.net/

Here's some live examples of the tools you can take a look at:

1. Click to Call: http://www.davidsuzuki.org/blogs/healthy-oceans-blog/2016/11/to-help-protect-canadas-oceans-weve-made-it-easy-to-call-your-mp/#newmode-embed-4-266

Check out this video of David Suzuki's d…

Me and varnish win against a DDOS attack.

This past month one of my servers experienced her first DDOS - a distributed denial of service attack. A denial of service attack (or DOS) just means an attempt to shut down an internet-based service by overwhelming it with requests. A simple DOS attack is usually relatively easy to deal with using the standard linux firewall called iptables.  The way iptables works is by filtering the traffic based on the incoming request source (i.e., the IP of the attacking machine). The attacking machine's IP can be added into your custom ip tables 'blacklist' to block all traffic from it, and it's quite scalable so the only thing that can be overwhelmed is your actual internet connection, which is hard to do.

The reason a distributed DOS is harder is because the attack is distributed from multiple machines. I first noticed an increase in my traffic about a day after it had started - it wasn't slowing down my machine, but it did show up as a spike in traffic. I quickly saw that…

CiviCRM's invoice_id field and why you should love the hash

I've been banging my head against a distracted cabal of developers who seem to think that a particular CiviCRM core design, which I'm invested in via my contributed code, is bad, and that it's okay to break it.

This post is my attempt to explain why it was a good idea in the first place.

The design in question is the use of a hash function to populate a field called 'invoice_id' in CiviCRM's contribution table. The complaint was that this string is illegible to humans, and not necessary. So a few years ago some code was added to core, that ignores the current value of invoice_id and will overwrite it, when a human-readable invoice is generated.

The complaint about human-readability of course is valid, and the label on the field is misleading, but the solution is terrible for several reasons I've already written about.

In this post, I'd like to explain why the use of the hash value in the invoice_id field is actually a brilliant idea and should be embrac…