ActiveSync (Z-Push) sync with Zarafa and Nokia N900

Recently i bought a Nokia N900 and started right away with configuring my Exchange (Zarafa) account, but i didn’t work.

Syncing a mobile phone works via Microsoft’s ActiveSync, in Zarafa’s case this is implemented via Z-Push.

After making a post on the Z-Push forum i got in contact with Andreas (a Z-Push) and he found out what the problem was. Z-Push implements Exchange 2003 and the Nokia N900 requires Exchange 2007.

Andreas started working on some fixes and after a few days of mailing he made an alpha version which also support the Nokia N900.

At the moment i am running the Alpha in conjunction with my Zarafa envirioment and it works fine, so for all the other N900 users, help is on its way!

Protecting yourself against a DDoS with varnish

Today we received another DDoS attack on of our clusters.

99% of the DDoS attacks we receive are floods on port 80, not really Syn Flood attacks, but just a large stream of garbage on port 80 from thousands of hosts. This results in Apache just spawning processes and eventually locking up.

About two weeks ago i read about Varnish, this high performance HTTP proxy also seems to be a real life-saver when it comes to DDoS attacks.

Since we were really out of options i gave Varnish a go and installed it on our webservers. I configured Apache to listen on 127.0.0.1:80 and Varnish to listen on the public IP.

After doing this on 10 webservers i sat back and watched everything getting back to life!

This is because Varnish only forwards a HTTP request to the backend (Apache in this case) when it is complete, so this protects Apache from getting al the garbage and spawning useless childs.

So if you ever get a DDoS (and i really hope not!), keep Varnish in mind for saving yourself!

At the moment Varnish really looks like a permanent solution in our hosting envirioment, with some special Apache modules you can make it a transparant proxy, see: mod_extract_forwarded2

rtc timer problems when running Asterisk in KVM

For our VOIP we use Asterisk ( www.sipcat.com ). Recently we migrated the server from a physical machine to a KVM virtual machine under Ubuntu 9.04

When searching around i found some problems around running Asterisk in a VM, but there were also some succes stories.

I kept getting the message:
rtc: lost some interrupts at 1024Hz

I was able to solve this by disabling APIC for this virtual machine, i kept ACPI enabled.