Thursday, December 30, 2010

Cloud Instance with Cloud-Init on KVM

I wanted to run an Ubuntu server cloud instance locally on KVM hypervisor. I also wanted to run cloud-init on the local setup in order to experiment a bit with it. So that means, downloading a UEC image, booting it under KVM, and passing cloud-init parameters to it as it boots. Much to my surprise things were far easier than I expected, all thanks to our rocking Ubuntu cloud team. Here's the script I cobbled together, most of it is basically a rip off from this UEC Images wiki page.

So what this does is, it:
  • Downloads a UEC image of natty server daily i386 if it doesn't exist
  • Sets a few variables
  • Creates a qcow disk image, shadowing/cowing/differencing the downloaded image. This is to keep the originally downloaded image pristine
  • Downloads some sample user-data and meta-data (warning, this runs arbitrary commands and injects keys inside your VM, only use for testing!). To experiment with cloud-init you'd have to modify the user-data to your liking
  • Runs a local simple webserver (port 8000)
  • Boots the cow image in a local kvm. As it boots, you'll notice on your terminal the following two requests being made "GET /meta-data" and "GET /user-data". Cloud-init uses this data to customize the image as it boots
  • Once you close kvm, kills the web-server
So all you need to do, is create an empty directory, put this script in it and run it
tarball=$(basename $uecnattyservercurrent)
[ -f ${tarball} ] || wget ${uecnattyservercurrent}
tar -Sxvzf ${tarball} | tee "${contents}"
cat natty-server-uec-i386.tar.gz.contents
base=$(sed -n 's/.img$//p' "${contents}")
kernel=$(echo ${base}-vmlinuz-*)
qemu-img create -f qcow2 -b ${img} disk.img
python -m SimpleHTTPServer &
kvm -drive file=disk.img,if=virtio,boot=on -kernel "${kernel}" -append "ro init=/usr/lib/cloud-init/uncloud-init root=/dev/vda ds=nocloud-net;s= ubuntu-pass=ubuntu"
kill $websrvpid

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