Re: Conflicting alternatives
On Fri 19 Feb 2021 at 17:22:25 (+1300), Richard Hector wrote:
> On 19/02/21 2:34 am, Andrei POPESCU wrote:
> > On Jo, 18 feb 21, 08:15:39, Dan Ritter wrote:
> > > Richard Hector wrote:
> > > > On 18/02/21 5:22 am, Greg Wooledge wrote:
> > > > > On Thu, Feb 18, 2021 at 12:06:37AM +0800, Kevin Shell wrote:
> > > > > > You could stop one and start the other,
> > > > > > there's no resources or port conflict.
> > > > > > I want to just keep both, not run them at the same time.
> > > > > Again, as stated at the start of this fiasco of a thread, Debian policy
> > > > > says that all daemons must be started up by default.
> > > > It is possible to install both nginx and apache2 at the same time. Both
> > > > presumably try to get port 80? Not sure how that resolves; I don't have a
> > > > machine I want to try it on at the moment.
> > >
> > > The order of events is:
> > >
> > > - install one. Change the listening port to something other than 80.
> > >
> > > - install the next.
> > >
> > > Web servers are built to interoperate with each other; it is not
> > > ridiculous to have a dozen web servers on a machine each
> > > listening to different ports, or listening on sockets and being
> > > proxied by a different web server.
> >
> > It seems to me the important difference is that it is comparatively easy
> > and common to interact with a webserver on a non-standard port, whereas
> > running a SMTP server on a non-standard port might be useful only in
> > very specific corner cases.
>
> There are multiple standard ports, though. E.g. one could easily run
> one MTA on port 25 for incoming mail, and another on 587 for outgoing.
That's just a statement of the desired outcome, but you can only
"easily run" that if you can easily configure it so.
So from Debian's point of view, you have to come up with simple
configurations (ie through those curses screens that dpkg-reconfigure
displays) that reliably set up either or neither or both MTAs in roles
that not only don't conflict with one another, but also dovetail so
that all the many necessary roles are covered. And that would be for
every pair of MTAs that Debian deemed co-installable,
For each MTA, you also have to ensure that their well-known recipes
for passing off work to other software (like MDAs) still work, else
Debian gets lumbered with supporting all the breakages that occur
(or, worse, loses reputation).
> My point, though, was that there's a precedent for daemons that
> default to listening on the same port, yet are co-installable. And
> which will, IIRC, throw errors on installation if you try it without
> paying special attention.
As Dan pointed out, Mail is Different. Fine; throw errors during
the installation—that's static. Throw some more during
configuration—ditto. That doesn't help much when you actually
start using the MTAs in anger. If you get something wrong, you
might never see the errors. Someone at the other end might.
I can well understand why Debian wouldn't want to support
such a scheme.
Cheers,
David.
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