[openstack-dev] [DevStack] Python dependencies: PyPI vs distro packages

Clint Byrum clint at fewbar.com
Wed Aug 7 06:21:09 UTC 2013

Excerpts from Joshua Harlow's message of 2013-08-06 21:03:58 -0700:
> It does seem sad that the state of package management is this bad. 
> It'd would be equally interesting to hear how others rollback changes (another thing yum doesn't do so well, since it doesn't have a good ability to rollback dependent changes, especially when said rollback would alter a lot of versions and requirements). Maybe apt does this better. Idk.
> How are others working through that? 

Roll back is an illusion. Time does not go in reverse.

In TripleO with Heat, the vision is to have known working images, and
unknown images. If an unknown image is mid-rollout and has problems,
the working image should be re-deployed. You can call this Rollback,
but it is really just a new deployment that is intended to be the same
as the old version.

Trying to do this piecemeal, package by package, means you suffer when
a packager has messed up a maintainer script or an admin has edited a
file in-place. Your root file-system's state has as much influence on
your overall system state as the database.

I'm not saying packages are not useful for system maintenance. But they
carry some penalties that only really start to matter when you have lots
of machines. Using a virtualenv and testing it for everything we know
we want to do means knowing when that virtualenv rolls out that it has
a good chance of performing the same way.

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