mirror of
http://git.haproxy.org/git/haproxy.git/
synced 2024-12-26 06:32:13 +00:00
074ebcde29
The following directories were moved from contrib/ to dev/ to make their use case a bit clearer. In short, only developers are expected to ever go there. The makefile was updated to build and clean from these ones. base64/ flags/ hpack/ plug_qdisc/ poll/ tcploop/ trace/
60 lines
2.7 KiB
Plaintext
60 lines
2.7 KiB
Plaintext
** Plug queueing disciplines **
|
|
|
|
The 'plug' qdisc type is not documented. It is even not supported
|
|
by traffic shaping tools like 'tc' from iproute2 package.
|
|
|
|
Such qdiscs have already been used by Yelp engineers but outside
|
|
of haproxy with libnl-utils tools (especially nl-qdisc-* tools)
|
|
to implement a workaround and make haproxy reloads work.
|
|
|
|
Indeed with such plug qdiscs coupled with iptables configurations
|
|
we are able to temporarily bufferize IP packets and to release them as
|
|
needed. So, they may be very useful to "synchronize" TCP sessions
|
|
or at higher level to put network applications in states approaching
|
|
the ones suspected to occur during bugs. Furthermore to be sure
|
|
to produce a correct bug fix, it may be useful to reproduce
|
|
as mush as needed such painful bugs. This is where plug qdiscs
|
|
may be useful.
|
|
|
|
To have an idea about how to use plug qdisc on the command line I highly recommend to
|
|
read Willy Tarreau blog here:
|
|
|
|
https://www.haproxy.com/blog/truly-seamless-reloads-with-haproxy-no-more-hacks/
|
|
|
|
which refers to this other one from Yelp:
|
|
|
|
https://engineeringblog.yelp.com/2015/04/true-zero-downtime-haproxy-reloads.html
|
|
|
|
The code found in plug_qdisc.c file already helped in fixing a painful bug hard to
|
|
fix because hard to reproduce. To use the API it exports this is quite easy:
|
|
|
|
- First your program must call plug_disc_attach() to create if not already created
|
|
a plug qdisc and use it (must be done during your application own already existing
|
|
initializations).
|
|
Note that this function calls plug_qdisc_release_indefinite_buffer() so that to
|
|
release already buffered packets before you start your application,
|
|
|
|
- then call plug_qdisc_plug_buffer() to start buffering packets incoming to your
|
|
plug qdisc. So they won't be delivered to your application,
|
|
|
|
- then call plug_qdisc_release_indefinite_buffer() to stop buffering the packets
|
|
incoming to your plug qdisc and release those already buffered.
|
|
So, that to be deliver them to your application.
|
|
|
|
This code is short and simple. But uses several libraries especially libnl-route module
|
|
part of libnl library. To compile haproxy and make it use the plug_qdisc.c code we had
|
|
to link it against several libnl3 library modules like that:
|
|
|
|
-lnl-genl-3 -lnl-route-3 -lnl-3 -lnl-cli-3
|
|
|
|
|
|
- Some references:
|
|
Libnl API documentation may be found here:
|
|
https://www.infradead.org/~tgr/libnl/doc/api/index.html
|
|
|
|
Kernel sources:
|
|
http://elixir.free-electrons.com/linux/latest/source/net/sched/sch_plug.c
|
|
|
|
Nice website about traffic shaping with queuing disciplines:
|
|
http://wiki.linuxwall.info/doku.php/en:ressources:dossiers:networking:traffic_control
|