* *

        \ o /
         \|/ 
          |         Y O U   R O C K !
         / \  _  
        /   \/
       /
      -

Tell me what Free Software looks like:

THIS is what Free Software looks like!

Nice move, Peter!



Peter Duffy said on Fri, 20 May 2022 18:31:36 +0100

>Quite a long time ago, I mentioned that I'd been tasked with upgrading
>some linux VMs running under Microsoft Azure, and had decided to try to
>use devuan. I then found that devuan wouldn't work under azure. The
>problem was walinuxagent - aka waagent and azurelinuxagent, the glue
>layer which sits between the azure infrastructure and linux, and
>enables azure to do things like start and stop VMs and collect stats
>and metrics. It didn't work properly under devuan.
>
>It turned out that there were actually two problems:
>
>- walinuxagent needs to know about each supported distro, and hadn't
>been told about devuan: the default for unsupported distros was to
>assume that systemd was present.
>
>- to determine the distro under which it was running, walinuxagent used
>the python function platform.linux_distribution. This was incapable of
>distinguishing between devuan and debian (when run under devuan, it
>claimed that the distro was debian).
>
>Figuring out the context of the problem was difficult. It wasn't a
>devuan problem, as the walinuxagent package is taken directly from the
>debian repo; it wasn't a debian problem as the problem was in
>walinuxagent; the first part of the problem could be fixed by telling
>walinuxagent about devuan; python already had a new module/function
>distro.linux_distribution which was able to distinguish between debian
>and devuan, and walinuxagent fell back to this if
>platform.linux_distribution was not found - but if the latter was
>available, it would use it.
>
>Eventually, I decided to work on this myself. The walinuxagent repo is
>on github, so I forked it onto my own github account. Adding devuan as
>a known distro was fairly trivial (there's a structure built into
>walinuxagent to enable extra distros to be added and to tell it whether
>or not to use systemd). I then wrote a chunk of extra python code which
>would be called whenever platform.linux_distribution() was called and
>returned a result of "debian", and would re-check to see if it was
>really devuan. I got this all to work, and created an azure VM running
>devuan (beowulf). It seemed to work fine (the VM has now been in
>service for over 1.5 years). I then raised a pull request on the
>upstream azure walinuxagent repo to merge my changes.
>
>My pull request was acknowledged and put up for a code review - but for
>some reason, nothing further happened for a long time (maybe it was to
>do with problems caused by the pandemic). I have to admit that I had
>concerns about my extra code. I'd done extensive testing - but it was a
>big chunk of code which referenced a number of things in the linux
>environment, any of which could change independently of walinuxagent. I
>was conscious that if it was merged into the main repo, it would
>eventually get run on every debian-based VM in azure, and if there was
>something that I'd overlooked and which caused problems, it would cause
>problems on all of them. To put it mildly, that would probably be Bad
>News.
>
>Then chimaera appeared - and from my point of view, there was one
>extremely useful enhancement: debian bullseye, and therefore devuan
>chimaera, had moved to python 3.9. In python 3.8, the buggy and
>unreliable platform.linux_distribution had been removed. This forced
>walinuxagent to use distro.linux_distribution - and as this could
>distinguish between debian and devuan, my extra python code wasn't
>needed any more. So I cancelled the old pull request and started again,
>and this time just made the changes to walinuxagent to allow it to
>recognise devuan and use non-systemd utilities and functions on the VM.
>I then raised another pull request on the azure walinuxagent upstream
>repo, and after correcting a few issues, I heard on Wednesday that my
>changes have been merged. So when the next release of walinuxagent
>appears in the distros, it should support devuan. This should make it
>generally possible to run devuan VMs under azure.
>
>If anyone wants to have a look at my code, it can be cloned from my
>github account: https://github.com/peter9370/WALinuxAgent The version
>which works on chimaera and hopefully later releases is in the branch
>"devuan_support_new". There's also a branch
>"devuan_support_pre_chimaera" which contains the version including my
>extra code, which worked on beowulf. I'm not sure when the next release
>is due: I'll keep an eye on the upstream repo.
>
>Apologies for the length of that - it's been a long journey, and
>difficult to summarise concisely.