Developing dep8 tests with LXC

[Serge Hallyn]

Quoting Jean-Baptiste Lallement (jean-baptiste.lallement at canonical.com):
> On 07/03/2013 11:53 AM, Robie Basak wrote:
> >I scratched an itch and implemented an adt-virt-lxc, as I couldn't find
> >that anybody else had worked on it.
> >
> >It's here: https://code.launchpad.net/~racb/ubuntu/saucy/autopkgtest/lxc
> >Or just grab the adt-virt-lxc binary from it, and run:
> >     autopkgtest (...) --- /path/to/downloaded/adt-virt-lxc saucy -s daily
> >
> >It uses the ubuntu-cloud LXC template. It assumes that you have
> >permission to "sudo lxc-{create,start,attach,stop,destroy}" which works
> >fine on cloud images.
> >
> 
> >So LXC seemed like a good solution. Now I can write tests for daemons
> >more easily.
> This is a great feature added to autopkgtest. Thanks for this work!
> 
> >
> >
> >A couple of issues with my code, which I'd like to fix with some
> >feedback:
> >
> >1. I currently hardcode the container name "test". How do I create a
> >unique new container name without racing to create it? A question for
> >Serge perhaps?
> You could use a slightly different approach but which in my opinion
> fits well with autopkgtest.
> What if you use an existing container as base and start an ephemeral
> container to run the tests on.
> 
> A first step would be to create the container outside of the
> virt-lxc driver with the same command you use in the driver
> currently:
> lxc-create -t ubuntu-cloud -n adt-base -- -i adt ...
> 
> Then start an ephemeral container with:
> sudo lxc-start-ephemeral -o adt-base -kd
> 
> (-k is important for point 2 as it gives you access to the
> underlying filesystem (maybe there is a way I dont know with tmpfs
> too) and for some tests you'll need more than the space available in
> tmpfs to run your tests)
> 
> ephemeral containers will save you the time of re-creating the
> container for each test and an easy way to revert to a base image
> with always the same state.

That sounds like an excellent solution.  The only dowside is that
historically sometimes overlayfs has gotten finicky especially when
playing with apparmor.  But I think those issues are all resolved now.

Otherwise, I'd just use mktemp.

> >2. How do I detect when the container is fully booted so that I can use
> >it? Using lxc-wait only gave me it from (I presume) the host's
> >perspective; the guest kept breaking things until I figured out that it
> >was cleaning /tmp after I had already started using it. For now, I've
> >got a sleep hack to avoid this. But how do I detect boot completion
> >properly? A question for Scott maybe?
> On first boot of the container, from the host and if you used an
> ephemeral container, you can monitor when the file /var/lib/lxc/<NAME>/delta0/var/lib/cloud/instances/lxc-*/boot-finished
> appears.
> 
> -- 
> Jean-Baptiste
> IRC: jibel