listen on IPs but do not fail if one is absent - ?

[Maxim Dounin]

Hello!

On Wed, Aug 03, 2022 at 09:50:10AM +0100, lejeczek via nginx wrote:

> On 13/02/2022 11:24, Francis Daly wrote:
> > On Sun, Feb 13, 2022 at 07:56:16AM +0000, lejeczek via nginx wrote:
> >> On 12/02/2022 13:26, Francis Daly wrote:
> >>> On Sat, Feb 12, 2022 at 10:11:25AM +0000, lejeczek via nginx wrote:
> > Hi there,
> >
> >>>> having multiple 'listen' with IPs or, just one 'listen' with a hostname
> >>>> which resolves to more than one IP - is it possible to tell Nginx not fail
> >>>> when one of IPs is absent, does not exist?
> >>> I think that stock nginx does not support that.
> >>>
> >>> There are possibly ways to avoid the failure; but they all fundamentally
> >>> are different ways to do "only bind to locally-existing addresses".
> >> I can confess I return to Nginx after long many years of a divorce and this
> >> curious fact - if Nginx cannot do that - will be a surprise to me.
> > Use cases tend to be addressed when a developer has the incentive to
> > write the code.
> >
> > If the feature that you are hoping for, has not been implemented in a
> > way that you are hoping for, then probably no-one cared enough to ensure
> > that it was done in that way.
> >
> Which amazes me a bit - I'd think that in this age of 
> clouds/virtualization/containers etc. removing iface or IP 
> or both(even hot-plugin hardware) is something what must 
> happen often, if not daily - why people would not need that 
> 'feature' and not think it's silly of Nginx to fail for that 
> reason? - amazes me.
> 
> Certainly this use case where IP does not exists - perhaps 
> different case would be where IP does exist but cannot be 
> bound to - should be allowed & easy to give to end users an 
> option to "bind" to such non-existent IP with 
> 'continue/remain/insist' or however devel want to call.
> 
> I read people replies and think they thought it was about 
> 'port' in my case, but I tried to make it clear it's the 
> IP/iface - so "*" does not address the issue I described.

It is not clear why "*" does not address the issue you've 
described.  You may want to be more specific.  In particular, 
please explain why

    listen *:80;
    listen 99.99.99.99:80;

does not work for you.

The only case I can imagine is when you are not allowed to listen 
on *:80 for some reason, and have to listen only on specific IP 
addresses instead.  This looks quite uncommon though, and usually 
instead suggests that IP addresses are perfectly fixed.

(See description of the "bind" parameter of the "listen" directive 
at http://nginx.org/r/listen for additional details.)

-- 
Maxim Dounin
http://mdounin.ru/