support reuse_port option when creating server

[hubo1016]

Python supports reuse_port socket option when creating server

https://docs.python.org/3/library/asyncio-eventloop.html#asyncio.AbstractEventLoop.create_server

With reuse_port you can start multiple processes binding with the same port, easily creating a load-balanced server. While it is possible to start each process on different port, it can be done much easier with reuse_port option.

[asvetlov]

Could be done by adding reuse_port parameter to TCPSite and family.
reuse_address should be supported as well.

[pfreixes]

From my knowledge and tests reuse port is fundamentally broken for epoll

https://idea.popcount.org/2017-03-20-epoll-is-fundamentally-broken-22/

There is a flag that is available since kernel 4.5 that allows you to achieve the same behaviour. Also glibc has to be at least 2.24. Most of the distributions do not have it.

Also take into account that this is only appliable for new connections which have the worst code path in terms of performance. Most scenarios relay on long live conections to achieve maximum performance.

[hubo1016]

@pfreixes Execuse me, I didn't find any relationship between reuse_port option to the link.
The underlying create_server() call in Python asyncio supports this option, it should not be any problem to allow user to set it...

[pfreixes]

Because of that @hubo1016

With reuse_port you can start multiple processes binding with the same port, easily creating a load-balanced server. While it is possible to start each process on different port, it can be done much easier with reuse_port option.

[hubo1016]

@pfreixes As far as I know, reuse_port does not create duplicated sockets, it creates independent sockets binding on the same port. dup() issues should not be related to this I think?
After all, if underlying Python implementation supports it, then we should support it and leave the choices to users.

[asvetlov]

@hubo1016 please prepare a Pull Request

[hubo1016]

@asvetlov
OK, I will try

[asvetlov]

Fixed by #2693

[lock]

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[new issue]: https://github.com/aio-libs/aiohttp/issues/new