[bind10-dev] Config migration (Was: IXFR to AXFR fallback)

[Michal 'vorner' Vaner]

Hello

On Tue, Apr 30, 2013 at 09:34:46AM -0700, JINMEI Tatuya / 神明達哉 wrote:
> My concern of this approach is that it'll be backward incompatible
> change.  If we can still allow incompatible changes, the easiest way
> is to simply migrate to the new semantics (probably renaming the
> option).  But I guess we now need to think about compatibility more
> seriously, after the public release version.  In that case a
> compromise would be to keep the option name, define the type as "any"
> so we can accept both boolean and strings, and support both old and
> new versions.

Compatibility is, of course, a concern. I think it is also time to start
thinking about some kind of automatic migration scripts, or something. My idea
would be to:

• Have a version in each spec file
• Store the version in the config too
• Allow the spec file to specify script name for migration version x → y.
• If the version stored in the config is older than the one in the spec file,
  look for the script to migrate, allowing multiple steps. If there's a „gap“
  between conversion versions, assume the versions don't need explicit
  conversion, that they are compatible themselves.

This would solve upgrades, because we could rename options, move them around,
etc. But we still don't have downgrades. Maybe we could use the same mechanism
and have scripts to go down in the versions too. Or at least ask for manual
inspection, highlighting the scripts that did the upgrade.

With regards

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Michal 'vorner' Vaner
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