Bug#766233: LXC breakage and workarounds when upgrading VMs to jessie

[Tomas Pospisek]

On Mon, 24 Nov 2014, Marco d'Itri wrote:

> On Nov 24, Tomas Pospisek <tpo_deb at sourcepole.ch> wrote:
>
>> My first proposed text for the release-notes is below. Please let me
>> know if you prefer me to submit a proper patch against a SVN checkout 
>> of ddp.
>
> Please also clarify that LXC containers *can* use systemd with no
> troubles if correctly configured.

and

On Mon, 24 Nov 2014, Marco d'Itri wrote:

> On Nov 24, Tomas Pospisek <tpo_deb at sourcepole.ch> wrote:
>
>> 1. As far as I understand this [1] is a patch for a template used to
>>    create a new jessie LXC VM. Am I thus correct in assuming it's of no
>>    use for the "upgrade a LXC VM from wheezy to jessie"?
>
> Yes, the configuration of existing servers will have to be updated
> manually.
>
>> Marco d'Itri mentioned a "correctly configured VM", maybe we'll get 
>> some additional input from him, on what's required in the wheezy to jessie
>> upgrade case.
>
> What I meant is the list of changes in the patch.

and

On Mon, 24 Nov 2014, Marco d'Itri wrote:

> On Nov 24, Tomas Pospisek <tpo_deb at sourcepole.ch> wrote:
>
>> Since there is 'systemd-detect-virt', would it be possible for the systemd
>> preinst to check for a LXC system and then to prompt the user with something
>> like this? :
>
> [text cut out]
>
> We will seriously consider merging such a patch, if somebody will
> provide one.

I have to disappoint you to some measure. Unfortunately Antonio's
patch [1] does *not* work on wheezy *hosts*. The reason is that lxc on 
wheezy is missing the settings lxc.autodev=1 and lxc.kmsg=0, that seem to 
be required in order to run a lxc VM with systemd in it.

I do not know what it would take in lxc proper in wheezy to enable the 
required functionality short of backporting a newer lxc version to wheezy. 
And I can't judge the risks associated with the latter.

Also, Daniel Baumann seems to hint that wheezie's kernel (on the 
host!) could be missing the required features for a newer LXC. I don't 
know anyting about that.


To resume
============
The current available options that we have for upgrading wheezy LXC guest 
to jessie are:

1. on hosts that run wheezy with guests that run wheezy:

    a) upgrade guest to jessie and do nothing depending on the outcome of
       #762194

    b) upgrade guest to jessie and switch back to sysvinit

    c) upgrade the host to jessie - see below

2. on hosts that run jessie with guests that run wheezy:

    d) upgrade the guest to jessie and apply Antonio's changes to the guest
      before it reboots


Further insight appreciated, thanks,
*t

[1] https://github.com/lxc/lxc/commit/a9bf60bab547013a9873a3fb9efe61155e8694b8