The principle behind this load balancing algorithm was first imagined
and modeled by Steen Larsen then iteratively refined through several
work sessions until it would totally address its original goal.
The purpose of this algorithm is to always use the smallest number of
servers so that extra servers can be powered off during non-intensive
hours. Additional tools may be used to do that work, possibly by
locally monitoring the servers' activity.
The first server with available connection slots receives the connection.
The servers are choosen from the lowest numeric identifier to the highest
(see server parameter "id"), which defaults to the server's position in
the farm. Once a server reaches its maxconn value, the next server is used.
It does not make sense to use this algorithm without setting maxconn. Note
that it can however make sense to use minconn so that servers are not used
at full load before starting new servers, and so that introduction of new
servers requires a progressively increasing load (the number of servers
would more or less follow the square root of the load until maxconn is
reached). This algorithm ignores the server weight, and is more beneficial
to long sessions such as RDP or IMAP than HTTP, though it can be useful
there too.
Gcc 4.4 enables strict aliasing by default, resuling in complaints
when casting struct sockaddr_storage to sockaddr_in. Not only doing
this does not provide any noticeable performance improvement, it also
presents a risk of strange bugs even when the compiler does not emit
a warning, so let's disable this optimization !
Hank A. Paulson suggested to add CPU=native to optimize the code for
the build machine. This makes sense in a lot of situations. Since it
is often possible to have both 32 and 64 bits supported on recent
systems, the ARCH=32 and ARCH=64 build options were also added.
The 'client.c' file now only contained frontend-specific functions,
so it has naturally be renamed 'frontend.c'. Same for client.h. This
has also been an opportunity to remove some cross references from
files that should not have depended on it.
In the end, this file should contain a protocol-agnostic accept()
code, which would initialize a session, task, etc... based on an
accept() from a lower layer. Right now there are still references
to TCP.
All files referencing the previous ebtree code were changed to point
to the new one in the ebtree directory. A makefile variable (EBTREE_DIR)
is also available to use files from another directory.
The ability to build the libebtree library temporarily remains disabled
because it can have an impact on some existing toolchains and does not
appear worth it in the medium term if we add support for multi-criteria
stickiness for instance.
Consistent hashing provides some interesting advantages over common
hashing. It avoids full redistribution in case of a server failure,
or when expanding the farm. This has a cost however, the hashing is
far from being perfect, as we associate a server to a request by
searching the server with the closest key in a tree. Since servers
appear multiple times based on their weights, it is recommended to
use weights larger than approximately 10-20 in order to smoothen
the distribution a bit.
In some cases, playing with weights will be the only solution to
make a server appear more often and increase chances of being picked,
so stats are very important with consistent hashing.
In order to indicate the type of hashing, use :
hash-type map-based (default, old one)
hash-type consistent (new one)
Consistent hashing can make sense in a cache farm, in order not
to redistribute everyone when a cache changes state. It could also
probably be used for long sessions such as terminal sessions, though
that has not be attempted yet.
More details on this method of hashing here :
http://www.spiteful.com/2008/03/17/programmers-toolbox-part-3-consistent-hashing/
It was becoming painful to have all the LB algos in backend.c.
Let's move them to their own files. A few hashing functions still
need be broken in two parts, one for the contents and one for the
map position.
With this change, all frontends, backends, and servers maintain a session
counter and a timer to compute a session rate over the last second. This
value will be very useful because it varies instantly and can be used to
check thresholds. This value is also reported in the stats in a new "rate"
column.
A new data type has been added : pipes. Some pre-allocated empty pipes
are maintained in a pool for users such as splice which use them a lot
for very short times.
Pipes are allocated using get_pipe() and released using put_pipe().
Pipes which are released with pending data are immediately killed.
The struct pipe is small (16 to 20 bytes) and may even be further
reduced by unifying ->data and ->next.
It would be nice to have a dedicated cleanup task which would watch
for the pipes usage and destroy a few of them from time to time.
Did a full compile of the 1.3.15.7 - 20081208 snapshot on Freebsd-7.x
recently, and noted that there needs to be a quick patch done on the
Makefile for bsd machines.
This was due to the stream_interface replacing the send data commands
in the rewrite Willy did a while ago.
Simple fix, and it compiled cleanly otherwise. Thanks for the work
Willy!
Cheers,
Ross.
-=
Sometimes it is useful to find out how a given binary version was
built. The build compiler and options are now provided for this,
and it's possible to get them with the -vv option.
Proxy listeners were very special and not very easy to manipulate.
A proto_tcp file has been created with all that is required to
manage TCPv4/TCPv6 as raw protocols, and provide generic listeners.
The code of start_proxies() and maintain_proxies() now looks less
like spaghetti. Also, event_accept will need a serious lifting in
order to use more of the information provided by the listener.
A new file, proto_uxst.c, implements support of PF_UNIX sockets
of type SOCK_STREAM. It relies on generic stream_sock_read/write
and uses its own accept primitive which also tries to be generic.
Right now it only implements an echo service in sight of a general
support for start dumping via unix socket. The echo code is more
of a proof of concept than useful code.
A new generic protocol mechanism has been added. It provides
an easy method to implement new protocols with different
listeners (eg: unix sockets).
The listeners are automatically started at the right moment
and enabled after the possible fork().
The version does not appear anymore in the Makefiles nor in
the include files. It was a nightmare to maintain. Now there
is a VERSION file which contains the major version, a VERDATE
file which contains the date for this version and a SUBVERS
file which may contain a sub-version.
A "make version" target has been added to all makefiles to
check the version. The GNU Makefile also has an update-version
target to update those files. This should never be used.
It is still possible to override those values by specifying
them in the equivalent make variables. By default, the GNU
makefile tries to detect a GIT repository and always uses the
version and date from the current repository. This can be
disabled by setting IGNOREGIT to a non-void value.
src/chtbl.c, src/hashpjw.c and src/list.c are distributed under
an obscure license. While Aleks and I believe that this license
is OK for haproxy, other people think it is not compatible with
the GPL.
Whether it is or not is not the problem. The fact that it rises
a doubt is sufficient for this problem to be addressed. Arnaud
Cornet rewrote the unclear parts with clean GPLv2 and LGPL code.
The hash algorithm has changed too and the code has been slightly
simplified in the process. A lot of care has been taken in order
to respect the original API as much as possible, including the
LGPL for the exportable parts.
The new code has not been thoroughly tested but it looks OK now.
It's now as easy as passing "DLMALLOC_SRC=<path_to_dlmalloc.c>" to
build with support for dlmalloc. The dlmalloc source is not provided
with haproxy in order to ensure that people will use either the most
recent, or the most suited version for their platform. The minimal
mmap size is specified in DLMALLOC_THRES, which defaults to 4096. It
should be increased on platforms with larger pages (eg: 8 kB on some
64 bit systems).
- acl: smarter integer comparison support in ACLs
- acl: specify the direction during fetches
- acl: provide the argument length for fetch functions
- acl: provide a reference to the expr to fetch()
- acl: implement matching on header values
- acl: support maching on 'path' component
- acl: permit to return any header when no name specified
- errorfile: use a local file to feed error messages
- negation in ACL conds was not cleared between terms
- fix segfault at exit when using captures
- improve memory freeing upon exit
- acl: support '-i' to ignore case when matching
- str2net() must not change the const char *
- provide default ACLs
- acl: distinguish between request and response headers
- added the 'use_backend' keyword for full content-switching
- acl: added the TRUE and FALSE ACLs.
- shut warnings 'is*' macros from ctype.h on solaris
- do not re-arm read timeout in SHUTR state
- optimize I/O by detecting system starvation
- the epoll FD must not be shared between processes
- limit the number of events returned by *poll*
- fixed ev_sepoll again by rewriting the state machine
- switched all timeouts to timevals instead of milliseconds
- improved memory management using mempools v2.
- several minor optimizations
- several fixes in ev_sepoll
- fixed some expiration dates on some tasks
- fixed a bug in connection establishment detection due to speculative I/O
- fixed rare bug occuring on TCP with early close (reported by Andy Smith)
- implemented URI hashing algorithm (Guillaume Dallaire)
- implemented SMTP health checks (Peter van Dijk)
- replaced the rbtree with ul2tree from old scheduler project
- new framework for generic ACL support
- added the 'acl' and 'block' keywords to the config language
- added several ACL criteria and matches (IP, port, URI, ...)
- cleaned up and better modularization for some time functions
- fixed list macros
- fixed useless memory allocation in str2net()
- store the original destination address in the session
This framework offers all other subsystems the ability to register
ACL matching criteria. Some generic matching functions are already
provided. Others will come soon and the framework shall evolve.
- modularized the polling mechanisms and use function pointers instead
of macros at many places
- implemented support for FreeBSD's kqueue() polling mechanism
- fixed a warning on OpenBSD : MIN/MAX redefined
- change socket registration order at startup to accomodate kqueue.
- several makefile cleanups to support old shells
- fix build with limits.h once for all
- ev_epoll: do not rely on fd_sets anymore, use changes stacks instead.
- fdtab now holds the results of polling
- implemented support for speculative I/O processing with epoll()
- remove useless calls to shutdown(SHUT_RD), resulting in small speed boost
- auto-registering of pollers at load time
select, poll and epoll now have their dedicated functions and have
been split into distinct files. Several FD manipulation primitives
have been provided with each poller.
The rest of the code needs to be cleaned to remove traces of
StaticReadEvent/StaticWriteEvent. A trick involving a macro has
temporarily been used right now. Some work needs to be done to
factorize tests and sets everywhere.
- rewriting either the status line or request line could crash the
process due to a pointer which ought to be reset before parsing.
- rewriting the status line in the response did not work, it caused
a 502 Bad Gateway due to an erroneous state during parsing
- fix reqadd when no option httpclose is used.
- removed now unused fiprm and beprm from proxies
- split logs into two versions : TCP and HTTP
- added some docs about http headers storage and acls
- added a VIM script for syntax color highlighting (Bruno Michel)
- fixed several bugs which might have caused a crash with bad configs
- several optimizations in header processing
- many progresses towards transaction-based processing
- option forwardfor may be used in frontends
- completed HTTP response processing
- some code refactoring between request and response processing
- new HTTP header manipulation functions
- optimizations on the recv() patch to reduce CPU usage under very
high data rates.
- more user-friendly help about the 'usesrc' keyword (CTTPROXY)
- username/groupname support from Marcus Rueckert
- added the "except" keyword to the "forwardfor" option (Bryan German)
- support for health-checks on other addresses (Fabrice Dulaunoy)
- makefile for MacOS 10.4 / Darwin (Dan Zinngrabe)
- do not insert "Connection: close" in HTTP/1.0 messages
- fix critical bug introduced with 1.3.6 : an empty request header
may lead to a crash due to missing pointer assignment
- hdr_idx might be left uninitialized in debug mode
- fixed build on FreeBSD due to missing fd_set declaration
- stats now support the HEAD method too
- extracted http request from the session
- huge rework of the HTTP parser which is now a 28-state FSM.
- linux-style likely/unlikely macros for optimization hints
- do not create a server socket when there's no server
- added complete support and doc for TCP Splicing
- replaced the wait-queue linked list with an rbtree.
- stats: swap color sets for active and backup servers
- try to guess server check port when unset
- a few bugfixes and cleanups
This patch from Sin Yu makes use of an rbtree for the wait queue,
which will solve the slowdown problem encountered when timeouts
are heterogenous in the configuration. The next step will be to
turn maintain_proxies() into a per-proxy task so that we won't
have to scan them all after each poll() loop.
This structure will consume 4 bytes per header to keep track of
headers within a request or a response without having to parse
the whole request for each regex. As it's not possible to allocate
only 4 bytes, we define a max number of HTTP headers. We set it
to (BUFSIZE+79)/80 so that 8kB buffers can contain 100 headers
(like Apache), resulting in 400 bytes dedicated to indexation,
or about 400/(2*8kB) ~= 2.4% of the memory usage.
Released 1.3.3 with the following changes :
- fix broken redispatch option in case the connection has already
been marked "in progress" (ie: nearly always).
- support regparm on x86 to speed up some often called functions
- removed a few useless calls to gettimeofday() in log functions.
- lots of 'const char*' cleanups
- turn every FD_* into functions which are faster on recent CPUs
- builds again on OpenBSD and Solaris
