One user reported that an indicator was missing in the statistics:
the number of times each server was selected by load balancing. It
is in fact the total number of sessions assigned to a server by the
load balancing algorithm. It should directly reflect the weight for
"fair" algorithms such as round-robin, since it will not account for
persistant connections.
It should help a lot tuning each server's weight depending on the
load it receives.
Because of a divide, it was possible to have a null weight during
a slowstart, which is pretty annoying, especially with a single
server and a long slowstart.
Also, fix the way we report the values in the stats page to avoid
confusion.
A new "timeout" keyword replaces old "{con|cli|srv}timeout", and
provides the ability to independantly set the following timeouts :
- client
- tarpit
- queue
- connect
- server
- appsession
Additionally, the "clitimeout", "contimeout" and "srvtimeout" values
are supported but deprecated. No warning is emitted yet when they are
used since the option is very new.
Other timeouts should follow soon now.
Now the connect timeout, tarpit timeout and queue timeout are
distinct. In order to retain compatibility with older versions,
if either queue or tarpit is left unset both in the proxy and
in the default proxy, then it is inherited from the connect
timeout as before.
It is not always handy to manipulate large values exprimed
in milliseconds for timeouts. Also, some values are entered
in seconds (such as the stats refresh interval). This patch
adds support for time units. It knows about 'us', 'ms', 's',
'm', 'h', and 'd'. It automatically converts each value into
the caller's expected unit. Unit-less values are still passed
unchanged.
The unit must be passed as a suffix to the number. For instance:
clitimeout 15m
If any character is not understood, an error is returned.
This new function accepts inputs in various default units, from
the microsecond to the day. It detects suffixes after numbers
and performs the appropriate conversions between the user's unit
and the program's unit, considering a unit-less number in the
default unit.
In order to avoid issues in the future, we want to restrict
the set of allowed characters for identifiers. Starting from
now, only A-Z, a-z, 0-9, '-', '_', '.' and ':' will be allowed
for a proxy, a server or an ACL name.
A test file has been added to check the restriction.
R.I. Pienaar reported to me that the init script provided with
haproxy did not correctly report the status of the rhstatus()
function. In fact this was caused by the "exit $RETVAL" instead
of "exit $?" at the end.
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.
Now we can compute the max place depending on the number of servers,
maximum weight and weight scale. The formula has been stored as a
comment so that it's easy to choose between smooth weight ramp up
and high number of servers. The default scale has been set to 16,
which permits 4000 servers with a granularity of 6% in the worst
case (weight=1).
Due to the fact that htons is defined as a macro, it's dangerous
to call it with auto-incremented arguments such as htons(f(++x)) :
src/standard.c: In function 'url2sa':
src/standard.c:291: warning: operation on 'curr' may be undefined
The solution is simply to store the intermediate result an pass it
to htons() at once.
Under certain circumstances, it is very useful to be able to fail some
monitor requests. One specific case is when the number of servers in
the backend falls below a certain level. The new "monitor fail" construct
followed by either "if"/"unless" <condition> makes it possible to specify
ACL-based conditions which will make the monitor return 503 instead of
200. Any number of conditions can be passed. Another use may be to limit
the requests to local networks only.
The new "nbsrv" ACL verb matches the number of active servers in a backend.
By default, it applies to the backend where it is declared, but optionally
it can receive the name of another backend as an argument in parenthesis.
It counts the number of enabled active servers first, then the number of
enabled backup servers.
AIX does not know about MSG_DONTWAIT. Fortunately, nearly all sockets
are already set to O_NONBLOCK, so it's not even required to change the
code. It was only necessary to add this fcntl to the log socket which
lacked it. The MSG_DONTWAIT value has been defined to zero when unset
in order to make the code cleaner and more portable.
Also, on AIX, "hz" is defined, which causes a problem with one function
parameter in time.c. It's enough to rename the parameter there. Last,
fix a missing #include <string.h> in proxy.c.
A new "throttle" column has been added to HTML and RAW stats to indicate
in percent, the level of throttling due to server warmup. The column is
empty at 100%.
The new 'slowstart' parameter for a server accepts a value in
milliseconds which indicates after how long a server which has
just come back up will run at full speed. The speed grows
linearly from 0 to 100% during this time. The limitation applies
to two parameters :
- maxconn: the number of connections accepted by the server
will grow from 1 to 100% of the usual dynamic limit defined
by (minconn,maxconn,fullconn).
- weight: when the backend uses a dynamic weighted algorithm,
the weight grows linearly from 1 to 100%. In this case, the
weight is updated at every health-check. For this reason, it
is important that the 'inter' parameter is smaller than the
'slowstart', in order to maximize the number of steps.
The slowstart never applies when haproxy starts, otherwise it
would cause trouble to running servers. It only applies when
a server has been previously seen as failed.
It's important to be able to distinguish between servers which are UP
and those which are UP but disabled via a 404 response. For this reason,
the status entries report "NOLB" instead of "UP", and the HTML page uses
darker colors. As a complement, write "DOWN" in bold red on the backend
if it has no server left for load balancing.
It's not always obvious for the callers of set_server_status_{up,down}
whether the new state really is up or down. Some flags as well as the
effective weight have to be considered. Let's ensure that those functions
perform the necessary check themselves so that if the state transition
cannot be performed, at least everything is updated as required.
When an HTTP server returns "404 not found", it indicates that at least
part of it is still running. For this reason, it can be convenient for
application administrators to be able to consider code 404 as valid,
but for a server which does not want to participate to load balancing
anymore. This is useful to seamlessly exclude a server from a farm
without acting on the load balancer. For instance, let's consider that
haproxy checks for the "/alive" file. To enable load balancing on a
server, the admin would simply do :
# touch /var/www/alive
And to disable the server, he would simply do :
# rm /var/www/alive
Another immediate gain from doing this is that it is now possible to
send NOTICE messages instead of ALERT messages when a server is first
disable, then goes down. This provides a graceful shutdown method.
To enable this behaviour, specify "http-check disable-on-404" in the
backend.
Hello,
You will find attached an updated release of previously submitted patch.
It polish some part and extend ACL engine to match IP and PORT parsed in
HTTP request. (and take care of comments made by Willy ! ;))
Best regards,
Alexandre
The number of possible options for a proxy has already reached
32, which is the current limit due to the fact that they are
each represented as a bit in a 32-bit word.
It's possible to move the load balancing algorithms to another
place. It will also save some space for future algorithms.
This round robin algorithm was written from trees, so that we
do not have to recompute any table when changing server weights.
This solution allows on-the-fly weight adjustments with immediate
effect on the load distribution.
There is still a limitation due to 32-bit computations, to about
2000 servers at full scale (weight 255), or more servers with
lower weights. Basically, sum(srv.weight)*4096 must be below 2^31.
Test configurations and an example program used to develop the
tree will be added next.
Many changes have been brought to the weights computations and
variables in order to accomodate for the possiblity of a server to
be running but disabled from load balancing due to a null weight.
Under some circumstances, it will be useful to be able to have
a server's effective weight bigger than the user weight, and this
is particularly true for dynamic weight-based algorithms. In order
to support this, we add a "wdiv" member to the lbprm structure
which will always be used to divide the weights before reporting
them.
Since the introduction of server weights, all load balancing algorithms
relied on a pre-computed map. Incidently, quite a bunch of map-specific
parameters were used at random places in order to get the number of
servers or their total weight. It was not architecturally acceptable
that optimizations for the map computation had impact on external parts.
For instance, during this cleanup it was found that a backend weight was
seen as 1 when only the first backup server is used, whatever its weight.
This cleanup consists in differentiating between LB-generic parameters,
such as total weights, number of servers, etc... and map-specific ones.
The struct proxy has been enhanced in order to make it easier to later
support other algorithms. The recount_servers() function now also
updates generic values such as total weights so that it's not needed
anymore to call recalc_server_map() when weights are needed. This
permitted to simplify some code which does not need to know about map
internals anymore.
It was possible to slightly reduce the size and the number of
operations in session_process_counters(). Two 64 bit comparisons
were removed, reducing the code by 98 bytes on x86 due to the lack
of registers. The net observed performance gain is almost 2%, which
cannot be attributed to those optimizations, but more likely to
induced changes in code alignment in other functions.
By default, counters used for statistics calculation are incremented
only when a session finishes. It works quite well when serving small
objects, but with big ones (for example large images or archives) or
with A/V streaming, a graph generated from haproxy counters looks like
a hedgehog.
This patch implements a contstats (continous statistics) option.
When set counters get incremented continuously, during a whole session.
Recounting touches a hotpath directly so it is not enabled by default,
as it has small performance impact (~0.5%).
It is very convenient for SNMP monitoring to have unique process ID,
proxy ID and server ID. Those have been added to the CSV outputs.
The numbers start at 1. 0 is reserved. For servers, 0 means that the
reported name is not a server name but half a proxy (FRONTEND/BACKEND).
A remaining hidden "-" in the CSV output has been eliminated too.
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.
