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Cloud images, qemu, cloud-init and snapd spread tests April 16, 2019

Posted by jdstrand in canonical, ubuntu, ubuntu-server, uncategorized.
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It is useful for testing to want to work with official cloud images as local VMs. Eg, when I work on snapd, I like to have different images available to work with its spread tests.

The autopkgtest package makes working with Ubuntu images quite easy:

$ sudo apt-get install qemu-kvm autopkgtest
$ autopkgtest-buildvm-ubuntu-cloud -r bionic # -a i386
Downloading https://cloud-images.ubuntu.com/bionic/current/bionic-server-cloudimg-amd64.img...
# and to integrate into spread
$ mkdir -p ~/.spread/qemu
$ mv ./autopkgtest-bionic-amd64.img ~/.spread/qemu/ubuntu-18.04-64.img
# now can run any test from 'spread -list' starting with
# 'qemu:ubuntu-18.04-64:'

This post isn’t really about autopkgtest, snapd or spread specifically though….

I found myself wanting an official Debian unstable cloud image so I could use it in spread while testing snapd. I learned it is easy enough to create the images yourself but then I found that Debian started providing raw and qcow2 cloud images for use in OpenStack and so I started exploring how to use them and generalize how to use arbitrary cloud images.

General procedure

The basic steps are:

  1. obtain a cloud image
  2. make copy of the cloud image for safekeeping
  3. resize the copy
  4. create a seed.img with cloud-init to set the username/password
  5. boot with networking and the seed file
  6. login, update, etc
  7. cleanly shutdown
  8. use normally (ie, without seed file)

In this case, I grabbed the ‘debian-testing-openstack-amd64.qcow2’ image from http://cdimage.debian.org/cdimage/openstack/testing/ and verified it. Since this is based on Debian ‘testing’ (current stable images are also available), when I copied it I named it accordingly. Eg, I knew for spread it needed to be ‘debian-sid-64.img’ so I did:

$ cp ./debian-testing-openstack-amd64.qcow2 ./debian-sid-64.img

I then resized it. I picked 20G since I recalled that is what autopkgtest uses:

$ qemu-img resize debian-sid-64.img 20G

These are already setup for cloud-init, so I created a cloud-init data file (note, the ‘#cloud-config’ comment at the top is important):

$ cat ./debian-data
#cloud-config
password: debian
chpasswd: { expire: false }
ssh_pwauth: true

and a cloud-init meta-data file:

$ cat ./debian-meta-data
instance-id: i-debian-sid-64
local-hostname: debian-sid-64

and fed that into cloud-localds to create a seed file:

$ cloud-localds -v ./debian-seed.img ./debian-data ./debian-meta-data

Then start the image with:

$ kvm -M pc -m 1024 -smp 1 -monitor pty -nographic -hda ./debian-sid-64.img -drive "file=./debian-seed.img,if=virtio,format=raw" -net nic -net user,hostfwd=tcp:127.0.0.1:59355-:22

(I’m using the invocation that is reminiscent of how spread invokes it; feel free to use a virtio invocation as described by Scott Moser if that better suits your environment.)

Here, the “59355” can be any unused high port. The idea is after the image boots, you can login with ssh using:

$ ssh -p 59355 debian@127.0.0.1

Once logged in, perform any updates, etc that you want in place when tests are run, then disable cloud-init for the next boot and cleanly shutdown with:

$ sudo touch /etc/cloud/cloud-init.disabled
$ sudo shutdown -h now

The above is the generalized procedure which can hopefully be adapted for other distros that provide cloud images, etc.

For integrating into spread, just copy the image to ‘~/.spread/qemu’, naming it how spread expects. spread will use ‘-snapshot’ with the VM as part of its tests, so if you want to update the images later since they might be out of date, omit the seed file (and optionally ‘-net nic -net user,hostfwd=tcp:127.0.0.1:59355-:22’ if you don’t need port forwarding), and use:

$ kvm -M pc -m 1024 -smp 1 -monitor pty -nographic -hda ./debian-sid-64.img

UPDATE 2019-04-23: the above is confirmed to work with Fedora 28 and 29 (though, if using the resulting image to test snapd, be sure to configure the password as ‘fedora’ and then be sure to ‘yum update ; yum install kernel-modules nc strace’ in the image).

UPDATE 2019-04-22: the above is confirmed to work with CentOS 7 (though, if using the resulting image to test snapd, be sure to configure the password as ‘centos’ and then be sure to ‘yum update ; yum install epel-release ; yum install golang nc strace’ in the image).

Extra steps for Debian cloud images without default e1000 networking

Unfortunately, for the Debian cloud images, there were additional steps because spread doesn’t use virtio, but instead the default the e1000 driver, and the Debian cloud kernel doesn’t include this:

$ grep E1000 /boot/config-4.19.0-4-cloud-amd64
# CONFIG_E1000 is not set
# CONFIG_E1000E is not set

So… when the machine booted, there was no networking. To adjust for this, I blew away the image, copied from the safely kept downloaded image, resized then started it with:

$ kvm -M pc -m 1024 -smp 1 -monitor pty -nographic -hda $HOME/.spread/qemu/debian-sid-64.img -drive "file=$HOME/.spread/qemu/debian-seed.img,if=virtio,format=raw" -device virtio-net-pci,netdev=eth0 -netdev type=user,id=eth0

This allowed the VM to start with networking, at which point I adjusted /etc/apt/sources.list to refer to ‘sid’ instead of ‘buster’ then ran apt-get update then apt-get dist-upgrade to upgrade to sid. I then installed the Debian distro kernel with:

$ sudo apt-get install linux-image-amd64

Then uninstalled the currently running kernel with:

$ sudo apt-get remove --purge linux-image-cloud-amd64 linux-image-4.19.0-4-cloud-amd64

(I used ‘dpkg -l | grep linux-image’ to see the cloud kernels I wanted to remove). Removing the package that provides the currently running kernel is a dangerous operation for most systems, so there is a scary message to abort the operation. In our case, it isn’t so scary (we can just try again ;) and this is exactly what we want to do.

Next I cleanly shutdown the VM with:

$ sudo shutdown -h now

and try to start it again like with the ‘general procedures’, above (I’m keeping the seed file here because I want cloud-init to be re-run with the e1000 driver):

$ kvm -M pc -m 1024 -smp 1 -monitor pty -nographic -hda ./debian-sid-64.img -drive "file=./debian-seed.img,if=virtio,format=raw" -net nic -net user,hostfwd=tcp:127.0.0.1:59355-:22

Now I try to login via ssh:
$ ssh -p 59355 debian@127.0.0.1
...
debian@127.0.0.1's password:
...
Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.
Last login: Tue Apr 16 16:13:15 2019
debian@debian:~$ sudo touch /etc/cloud/cloud-init.disabled
debian@debian:~$ sudo shutdown -h now
Connection to 127.0.0.1 closed.

While this VM is no longer the official cloud image, it is still using the Debian distro kernel and Debian archive, which is good enough for my purposes and at this point I’m ready to use this VM in my testing (eg, for me, copy ‘debian-sid-64.img’ to ‘~/.spread/qemu’).

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