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

[Colin Walters <walters verbum org>]

On Tue, Dec 13, 2016, at 12:45 PM, Clayton Coleman wrote:

Are the POSIX issues in applications running on overlay mostly resolved now?  I.e. if we flipped the default would be reasonably able to support a diverse range of Linux workloads without the risk that previously existed?

overlayfs will never be fully POSIX compatible, but I think that's OK,

because remember - you shouldn't use overlayfs for persistent data,

or really anything that's not code/config files (and we want to get

to where that's overlayfs-type semantics for builds, and read-only

for deployment).  Data should be in Kube persistent volumes etc.

I think the thing to focus on is tools that are run during builds - the

yum-in-overlayfs bug is a good example, because the RPM database

*is* a database which is the type of workload that's going to

be sensitive to the overlayfs semantics.  How many of those

are there?  Probably not many, I suspect most of the compat

issues with userspace have been shaken out by now.

(But long term we may end up in a situation where people

 who want to run e.g. rhel5's yum in a container need to

 somehow fall back to devmapper)