Which modules do you "allow" yourself to use for production?

David Cantrell david at cantrell.org.uk
Tue Jul 23 12:23:27 BST 2013

On Mon, Jul 22, 2013 at 09:39:33PM +0100, Dirk Koopman wrote:

>                                                               And yes, I 
> would advise against producing production code that has lots of external 
> (CPAN) dependencies, especially if the normal path through those modules 
> touches most of them. There are numerous (horror) stories of what can 
> happen when one wants to update something, say a perl or a major CPAN 
> component with many dependencies.

But you have this problem in any language, not just perl.

I'm happy to use loads of stuff from the CPAN, but not to use it
straight from the CPAN.  Ideally, you'll build your own packages from
your CPAN dependencies (deb, rpm or whatever), as well as building a
package for your application that depends on them all. That way you
stay in control and can be sure that all your machines have the same
version of everything.

If you do that it's a good idea to keep those packages, including
the package that contains your build of perl, reasonably up-to-date.
This will minimise the pain of upgrading (you'll just have to deal with
occasional small incompatibilities instead of a many-tentacled horror)
and you'll also have a procedure right from the start for dealing with
upgrades, so when you actually *need* to upgrade it won't be so fraught
with peril.

As an alternative to building your own packages, use a CPAN mirror that
doesn't randomly change, such as http://cp2013-06an.barnyard.co.uk/
which is the CPAN as it was at 2013-06-01Z00:00:00. Then every so often
change to using a later snapshot in dev and when it's all working again
use that later snapshot in your other environments. Of course, if you go
this way you'll probably want to have separate dev and maint
environments for your programmers. But that's OK, any machine built in
the last five years can run multiple virtual machines.

David Cantrell | Reality Engineer, Ministry of Information

  I remember when computers were frustrating because they did
  exactly what you told them to.  That seems kinda quaint now.
      -- JD Baldwin, in the Monastery

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