[Web-SIG] Starting Web Servers using socket FDs

[Roberto De Ioris]

Il giorno 05/giu/2012, alle ore 11:30, Tarek Ziadé ha scritto:

> Hey 
> 
> I am doing this experimentation where the WGSI server is not started with an host/port or a unix socket, but rather a FD value, 
> corresponding to a socket already bound by the parent process. 
> 
> The server would then just accept new connection on the FD, using socket.fromfd() to get a socket object back, 
> and forget about all the binding work. 
> 
> Here's a prototype based on wsgiref : https://github.com/tarekziade/chaussette 
> 
> The goal I have is to be able to just spawn web workers using subprocess and take care myself  of the process 
> management part.  I wrote a blog post on my motivations here : http://blog.ziade.org/2012/06/12/shared-sockets-in-circus 
> if you want more background. 
> 
> Anyways, the idea I wanted to bring here was the following: 
> 
> most web servers out there support regular host/port or Unix Socket, which are usually the "unix:" prefix followed by a path on the system. 
> 
> What if web servers had these two standards *and* a new one which would be a "fd:" prefix. 
> 
> For instance, we would start server foo with: 
> 
> $ foo --fd:12:localhost:8080 
> 
> Where 12 is the fd number the foo server would use for getting the socket, and "localhost:8080" would just be there 
> as an information to be able to fill some WGSI headers that requires it. 
> 
> From there I could just spawn "foo" and pass to it socket.fileno() 
> 
> Thoughts ? 
> 

This is the approach used by fastcgi (even if only on file descriptor 0), old inetd-style daemons, and newer upstart and systemd daemons.

Gunicorn can already bind (or better, accept) from file descriptors specifying an environment variable. uWSGI supports by-default the inheritance of file descriptor 0 for fcgi-like startup,
and working on generic file descriptor or inet/upstart/systemd socket activation.

The vast majority of modern systems expects the file descriptor number on an environment variable:

upstart: UPSTART_FDS
systemd: LISTEN_FDS

Circus, could follow the same behaviour, but i do not know if a standard will be required for that.

Regarding the --fd:12:localhost:8080 syntax, is redundant as you can get the name of the socket mapped to a file descriptor
with getsockname:

http://linux.die.net/man/2/getsockname

--
Roberto De Ioris
http://unbit.it
JID: roberto at jabber.unbit.it