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Dear colleagues,

As might remember, we introduced Docker containers on the master node a
while ago when we implemented first version of Fuel upgrade feature. The
motivation behind was to make it possible to rollback upgrade process if
something goes wrong.

Now we are at the point where we can not use our tarball based upgrade
approach any more and those patches that deprecate upgrade tarball has been
already merged. Although it is a matter of a separate discussion, it seems
that upgrade process rather should be based on kind of backup and restore
procedure. We can backup Fuel data on an external media, then we can
install new version of Fuel from scratch and then it is assumed backed up
Fuel data can be applied over this new Fuel instance. The procedure itself
is under active development, but it is clear that rollback in this case
would be nothing more than just restoring from the previously backed up
data.

As for Docker containers, still there are potential advantages of using
them on the Fuel master node, but our current implementation of the feature
seems not mature enough to make us benefit from the containerization.

At the same time there are some disadvantages like

   - it is tricky to get logs and other information (for example, rpm -qa)
   for a service like shotgun which is run inside one of containers.
   - it is specific UX when you first need to run dockerctl shell
   {container_name} and then you are able to debug something.
   - when building IBP image we mount directory from the host file system
   into mcollective container to make image build faster.
   - there are config files and some other files which should be shared
   among containers which introduces unnecessary complexity to the whole
   system.
   - our current delivery approach assumes we wrap into rpm/deb packages
   every single piece of the Fuel system. Docker images are not an exception.
   And as far as they depend on other rpm packages we forced to build
   docker-images rpm package using kind of specific build flow. Besides this
   package is quite big (300M).
   - I'd like it to be possible to install Fuel not from ISO but from RPM
   repo on any rpm based distribution. But it is double work to support both
   Docker based and package based approach.

Probably some of you can give other examples. Anyway, the idea is to get
rid of Docker containers on the master node and switch to plane package
based approach that we used before.

As far as there is nothing new here, we just need to use our old site.pp
(with minimal modifications), it looks like it is possible to implement
this during 8.0 release cycle. If there are no principal objections, please
give me a chance to do this ASAP (during 8.0), I know it is a huge risk for
the release, but still I think I can do this.




Vladimir Kozhukalov
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