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Old 07-06-2011, 06:08 AM
Leonid Borisenko
 
Default How to warn user about breaking change in location of runtime file?

Hi,

I'm maintainer of uWSGI package and want to introduce in next version
of package possibly breaking change in location of runtime file.

uWSGI is a (web-)application server and usually is proxied by
Apache2/Nginx/Cherokee via communication socket. uWSGI init.d script,
provided by uwsgi package, guarantees creation of UNIX socket in
'/run/uwsgi/<confname>/socket' (where <confname> is the name of
user-made configuration file seen by init.d script).

I want to move socket location from '/run/uwsgi/<confname>/socket' to
'/run/uwsgi/app/<confname>/socket'. If user relied on socket location,
then upgrade of uwsgi package will require manual editing of frontend
server configuration. Until editing (and reloading of upstream server),
behavior of the whole server stack will be broken.

So I want to provide visible warning about introduced change in socket
location. And I'm curious about how to do it right.

I've asked about it in debian-mentors [1]. In short: I've asked for
advice in choosing between: 1) mentioning of change in NEWS.Debian, 2)
providing debconf note, 3) both 1. and 2., 4) something else. I've
recieved no answers though.

Since then, I've found that similar questions were discussed in
debian-devel some years ago (I've found threads from 2006, 2007 years).
And the conclusion was to use of NEWS.Debian exclusively (and to not
abuse debconf). I've also found and read relevant sections of Debian
Developer's Reference: 6.3.4 and 6.5.1. These sections also recommends
to use NEWS.Debian only.

So I assume that mentioning of change in NEWS.Debian only is the right
way. Is it still true? Or there is more preferred way to warn user?

[1] http://lists.debian.org/debian-mentors/2011/06/msg00273.html


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Old 07-06-2011, 07:22 AM
Jonathan Nieder
 
Default How to warn user about breaking change in location of runtime file?

Hi,

Leonid Borisenko wrote:

> I want to move socket location from '/run/uwsgi/<confname>/socket' to
> '/run/uwsgi/app/<confname>/socket'. If user relied on socket location,
> then upgrade of uwsgi package will require manual editing of frontend
> server configuration. Until editing (and reloading of upstream server),
> behavior of the whole server stack will be broken.
[...]
> I've asked about it in debian-mentors [1]. In short: I've asked for
> advice in choosing between: 1) mentioning of change in NEWS.Debian, 2)
> providing debconf note, 3) both 1. and 2., 4) something else. I've
> recieved no answers though.

uwsgi was never in a stable release and users have only had a few
weeks to get used to the current behavior, so I'd suggest mentioning
the change and what configuration change might be needed in
NEWS.Debian and leaving it at that.

Still, I like this question so much that I think it deserves a more
thorough answer. So imagine that the old socket location had been
used for a longer period; what could you do? Just mentioning the
change in NEWS is not so pleasant, since it requires action on the
part of the sysadmin. In that case, I believe your best option would
be to provide a symlink in /run/uwsgi/<confname>/socket to the new
location and file a bug against the release-notes package to document
that this symlink would disappear in (next Debian release)+1.

In some configurations, a debconf note blocks the installation until a
human has acknowledged it, which might seem like an appealing feature.
NEWS.Debian.gz entries work even better (if apt-listchanges is
installed), since they are shown before the preconfiguration stage of
an upgrade begins, allowing the administrator to back out if it is not
a good time. Once an upgrade begins, they do not interfere, and after
the upgrade, they are easy to inspect automatically or by hand. The
reasons described at[*] also apply, of course.

Thanks for your work, and hope that helps.
Jonathan
[*] http://www.debian.org/doc/manuals/developers-reference/best-pkging-practices.html#s6.5.1


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Old 07-07-2011, 10:26 AM
Leonid Borisenko
 
Default How to warn user about breaking change in location of runtime file?

Hi Jonathan,

Thanks for comprehensive and very helpful answer!

[top-posted because it was difficult to find something valueless to
skip for getting rid of reply scrolling]

On 06.07.2011 10:22, Jonathan Nieder wrote:
> Hi,
>
> Leonid Borisenko wrote:
>
>> I want to move socket location from '/run/uwsgi/<confname>/socket' to
>> '/run/uwsgi/app/<confname>/socket'. If user relied on socket location,
>> then upgrade of uwsgi package will require manual editing of frontend
>> server configuration. Until editing (and reloading of upstream server),
>> behavior of the whole server stack will be broken.
> [...]
>> I've asked about it in debian-mentors [1]. In short: I've asked for
>> advice in choosing between: 1) mentioning of change in NEWS.Debian, 2)
>> providing debconf note, 3) both 1. and 2., 4) something else. I've
>> recieved no answers though.
>
> uwsgi was never in a stable release and users have only had a few
> weeks to get used to the current behavior, so I'd suggest mentioning
> the change and what configuration change might be needed in
> NEWS.Debian and leaving it at that.
>
> Still, I like this question so much that I think it deserves a more
> thorough answer. So imagine that the old socket location had been
> used for a longer period; what could you do? Just mentioning the
> change in NEWS is not so pleasant, since it requires action on the
> part of the sysadmin. In that case, I believe your best option would
> be to provide a symlink in /run/uwsgi/<confname>/socket to the new
> location and file a bug against the release-notes package to document
> that this symlink would disappear in (next Debian release)+1.
>
> In some configurations, a debconf note blocks the installation until a
> human has acknowledged it, which might seem like an appealing feature.
> NEWS.Debian.gz entries work even better (if apt-listchanges is
> installed), since they are shown before the preconfiguration stage of
> an upgrade begins, allowing the administrator to back out if it is not
> a good time. Once an upgrade begins, they do not interfere, and after
> the upgrade, they are easy to inspect automatically or by hand. The
> reasons described at[*] also apply, of course.
>
> Thanks for your work, and hope that helps.
> Jonathan
>
>[*] http://www.debian.org/doc/manuals/developers-reference/best-pkging-practices.html#s6.5.1
>
>


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