Fibers web server: use multiple server sockets

Fibers web server: use multiple server sockets

[Vivien Kraus]

Dear guile fiber users,

Fibers is a library that I would very much like to use. It provides a
nice web server. However, as I recently discovered, in a standard
GNU/Linux server, not all network interfaces and addresses are up when
the server is about to start (especially so with dhcp). I have a nice
solution for that: every now and then, the server calls getaddrinfo. If
a previously bound address does not appear anymore in the return value,
then close the socket it was bound to. If a new address is returned by
the function, create a new socket for it and bind it to the new address
(and listen). This means that if a new address appears for the host
argument, then the server will eventually listen to it without having
to restart anything. If an address is dropped, eventually the server
will stop listening to it.

I would like to have that in the fibers web server. However, I
understand that not everyone would want it, or some would do it
differently (e.g. by using guile-netlink or something else). I think
the web server should make “listen”, “fcntl” (for set-nonblocking!) and
“accept” generic (with parameters, or GOOPS, or…?) so that I could fit
my weird thing within the call to accept.
Ultimately, everything could be expressed in terms of “accept” and have
the default implementation call listen and set-nonblocking! lazily
during the first call to accept. 

What do you think? Should the fibers web server try to do the
getaddrinfo thing by itself or be extensible and let me do it myself?
Are you OK with GOOPS? Do you prefer parameters? Do you have other
options?

Best regards,

Vivien

RE: Fibers web server: use multiple server sockets

[dsmich]

> From: "Vivien Kraus" 
> To: "guile-user"
> Sent: Wednesday November 2 2022 12:38:05PM
> Subject: Fibers web server: use multiple server sockets

> Fibers is a library that I would very much like to use. It provides
a
> nice web server. However, as I recently discovered, in a standard
> GNU/Linux server, not all network interfaces and addresses are up
when
> the server is about to start (especially so with dhcp). I have a
nice
> solution for that: every now and then, the server calls getaddrinfo.

How about not starting the web server until network interfaces are
fully up?

-Dale

Re: Fibers web server: use multiple server sockets

[Vivien Kraus]

Hello Dale,

There are 2 init systems that matter: shepherd (because it’s guile and
used in guix) and systemd (because nearly everyone uses it).

Le mercredi 02 novembre 2022 à 18:15 +0000, dsmich@roadrunner.com a
écrit :
> How about not starting the web server until network interfaces are
> fully up?

As far as I understand, there is no such thing with shepherd. As for
systemd, this [1] is an interesting read and it shows that it’s up to
me to write my server such that it can adapt to dynamic configuration
changes.

[1] https://systemd.io/NETWORK_ONLINE/

Vivien

Re: Fibers web server: use multiple server sockets

[tomas]

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On Wed, Nov 02, 2022 at 06:15:15PM +0000, dsmich@roadrunner.com wrote:
> > From: "Vivien Kraus" 
> > To: "guile-user"
> > Sent: Wednesday November 2 2022 12:38:05PM
> > Subject: Fibers web server: use multiple server sockets
> 
> > Fibers is a library that I would very much like to use. It provides
> a
> > nice web server. However, as I recently discovered, in a standard
> > GNU/Linux server, not all network interfaces and addresses are up
> when
> > the server is about to start (especially so with dhcp). I have a
> nice
> > solution for that: every now and then, the server calls getaddrinfo.
> 
> How about not starting the web server until network interfaces are
> fully up?

As far as I understand Vivien, interfaces come and go during the
server's lifetime. I.e. it's not just a "boot" thing. This seems
like a valid use case.

You could, of course, restart the server every time an interface
moves...

Cheers
-- 
t

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Re: Fibers web server: use multiple server sockets

[Dr. Arne Babenhauserheide]

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<tomas@tuxteam.de> writes:
> As far as I understand Vivien, interfaces come and go during the
> server's lifetime. I.e. it's not just a "boot" thing. This seems
> like a valid use case.
On some servers you might actually pull out an interface during runtime
to hotswap a new one — for example because it signaled that it is short
of failing.

Best wishes,
Arne
-- 
Unpolitisch sein
heißt politisch sein,
ohne es zu merken.
draketo.de

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Re: Fibers web server: use multiple server sockets

[tomas]

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On Wed, Nov 02, 2022 at 08:35:24PM +0100, Dr. Arne Babenhauserheide wrote:
> 
> <tomas@tuxteam.de> writes:
> > As far as I understand Vivien, interfaces come and go during the
> > server's lifetime. I.e. it's not just a "boot" thing. This seems
> > like a valid use case.
> On some servers you might actually pull out an interface during runtime
> to hotswap a new one — for example because it signaled that it is short
> of failing.

Yes, but as Vivien explained his case, just the other side of the network
might go down. Or the dhcp server at the other side takes too long and we
don't want to block the boot. Or the sysadmin just does "ifdown eth0"
and somewhat later "ifup...". Or whatever.

Cheers
-- 
t

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Re: Fibers web server: use multiple server sockets

[Ricardo Wurmus]

tomas@tuxteam.de writes:

> [[PGP Signed Part:Undecided]]
> On Wed, Nov 02, 2022 at 08:35:24PM +0100, Dr. Arne Babenhauserheide wrote:
>> 
>> <tomas@tuxteam.de> writes:
>> > As far as I understand Vivien, interfaces come and go during the
>> > server's lifetime. I.e. it's not just a "boot" thing. This seems
>> > like a valid use case.
>> On some servers you might actually pull out an interface during runtime
>> to hotswap a new one — for example because it signaled that it is short
>> of failing.
>
> Yes, but as Vivien explained his case, just the other side of the network
> might go down. Or the dhcp server at the other side takes too long and we
> don't want to block the boot. Or the sysadmin just does "ifdown eth0"
> and somewhat later "ifup...". Or whatever.

Expanding on “whatever”: it may be a virtual network interface.  In an
unshared net namespace we can move one end of a veth device into the
container’s net namespace — and we can just as well move it out again or
destroy it by removing its host-side counterpart.

An example of this is shown here:
https://guix.gnu.org/cookbook/en/html_node/Container-Networking.html

-- 
Ricardo