Question

I am planning to install Hudson on Amazon EC2 using Ubuntu image. The code I am going to test does not have a big memory overhead – I will be executing mainly python unit tests.

Which EC2 instance should I use? Would micro instance be sufficient (have enough memory) or should I use a bigger instance?

Answer 1

Jenkins itself will happily run on a micro, but there are two problems: 1) you won’t have much memory left for building and testing, around 150MB, but the bigger problem is 2) if your CPU usage spikes for more than a few seconds Amazon will simply crush your instance with throttling cutting off 97% or more of available CPU. ^{http://gregsramblings.com/2011/02/07/amazon-ec2-micro-instance-cpu-steal/}

The throttling was completely impossible for us, making a build with testing take 12 minutes on EC2 instead of 25 seconds on a quad i7 laptop.

But! There’s a fix for the frugal:

Run a Jenkins master on a micro, but start up a small instance when needed to run the actual tests. That gives us plenty of memory and decent CPU, yet it’s still incredibly cheap (ten cents per push [or commit]). However, it substantially increases build time because it has to boot the instance and all that.

The setup is rather involved, and requires working around some limitations of the ec2 plugin (which, overall, works extremely well), so we wrote up a blog post if you want to do this: http://wkmacura.tumblr.com/post/5416465911/jenkins-ec2