Re: [atomic-devel] Fedora 26 change: using overlayfs as default

[Vivek Goyal <vgoyal redhat com>]

On Thu, Dec 15, 2016 at 09:18:35AM -0800, Josh Berkus wrote:
> Dan, Dusty, Vivek:
> 
> So far nobody has defined (technically) the exact problem with overlayfs
> and how it affects applications which want to write data inside the
> container.
> 
> Note that just saying "don't use Overlay for persistent data" really
> isn't good enough.  Apps in containers frequently write data to places
> users aren't aware of, such as writing port information to /var/run.
> While this data may not be important to the user, the app will fail if
> it errors out.
> 
> Pushing a change which will cause 30% of a user's containers to start
> failing for reasons which are opaque to them is not something we should
> do lightly.

Hi Josh,

While overlayfs is not posix compliant but I think it is now in a shape
where I expect a very small percentage of people to be affected. And
if we make it default, that's the way to figure out what are the corner
cases people care about and fix them in kernel.

I think pros of overlayfs might outweigh its cons. Also this change will
not affect existing users over upgrade. And if overlayfs does not work
for a user, switching back to devmapper should be easy.

- atomic storage reset
- edit /etc/sysconfig/docker-storage-setup and set
  STORAGE_DRIVER=devicemapper
- restart docker

Vivek
> 
> -- 
> --
> Josh Berkus
> Project Atomic
> Red Hat OSAS