IPv6 Support

[Olly Betts]

On Tue, 5 Apr 2022 at 11:33, Sam Pearson <sam at mysociety.org> wrote:
> We're working on a migration into a new infrastructure which uses IPv6
> exclusively internally, so our back-end application servers do not
> have IPv4 addresses other than a loopback address. Although we access
> our indexes directly from the filesystem we use replication to
> maintain real-time standby copies and to allow us to take consistent
> backups from the replicated copies.
>
> We're running on Debian Bullseye using the packages from the main
> Debian repositories, as of now version 1.4.18-3. I see the comments on
> https://trac.xapian.org/ticket/374 suggest that IPv6 support for the
> network features may be coming in 1.5 but isn't currently planned for
> 1.4.x due to concerns over backwards compatibility - unless perhaps
> there's some demand :)

Yes, there is IPv6 support in git master.

I had a look and the changes are fairly self-contained so it should
be feasible to backport (there are several later tweaks that would need
to be gathered up though).

However if we did backport this then upgrading a system which currently
works could potentially break in some scenarios (when there are IPv6
addresses but replication or remote TCP backend connections will fail
with them - e.g. due to firewall rules having only been added for the
IPv4 addresses).  That seems more acceptable in a new release series
than a point release late on in the life of a stable branch, but I
have little idea how common such problems would be in practice.

> I appreciate that there isn't a huge demand for this feature, but I'd
> appreciate an idea of how long it might be before this may be
> available in a released version so that we can make a decision
> internally here on how to work around this in the meantime. This might
> include building some packages of our own that include the relevant
> changes, so could potentially be useful to the project in terms of
> testing.

I'm hoping we can get a new stable release series out later this year.

On Mon, Apr 11, 2022 at 08:07:40PM +0100, Sam Pearson wrote:
> I just thought that I'd follow this up briefly to say that we're
> successfully working around this for the time being using Nginx as a
> reverse proxy. I'd be happy to share more details if anyone was interested.

If the reverse proxy trick doesn't work out, building a custom Debian
package isn't hard to do.  I think for that you'd only need the original
commit for that as the later changes seem to be for WIN32 or android.

Cheers,
    Olly