.TH BALANCE 1 2007/01/15
.SH NAME
balance 3.35 \- A simple TCP proxy with load balancing and failover mechanisms.
.SH SYNOPSIS
.B balance 
[
.B -b addr
]
[
.B -B addr
]
[ 
.B -t sec
]
[ 
.B -T sec
]
[
.B -adfpHM
] port host1[:port1[:maxc]] [!|%] [ ... hostn[:portn[:maxc]]] 
.PP
.B balance
[
.B -b addr 
]
.B -i
[
.B -d
] [
.B -M
] port
.PP
.B balance
[
.B -b addr
]
.B -c cmd
[
.B -d
]
[
.B -M
] port
.SH DESCRIPTION
.I Balance
is a simple, generic "userland" TCP proxy, which allows simple
round-robin load balancing and graceful failover between
several destination servers.
.PP
.I Balance 
is available at http://balance.sourceforge.net.  
.PP
.I Definitions:
A possible destination consisting of a host address and a port is called a "channel". 
A channel is member of a "channel group". Channels are numbered in a group
starting with 0.  Groups are numbered starting with 0, which is the
initial default group.  
.PP
.I Balance
accepts connections on the given port and forwards them to the supplied channels.
At least one channel (in the default group) must be specified. 
If there are two or more channels specified in a group
.I balance
performs a simple round-robin load balancing between the channels. 
.PP
.I Balance
allows the definition of further channel groups. The connection scheme works as
follows: 
.I balance
tries first to establish a connection to a channel in the first group (0), performing 
the standard round-robin load balancing scheme. If no channel in this group is available,
.I balance
proceeds with the next higher channel group. Groups are simply 
separated with a "!" at the command line at startup and can be controlled 
interactively with the "group" command.
.PP
A "%" instead of a "!" as a group separator declares the previous group to be of type "hash".
This means that instead of a round-robin algorithm, a hash distribution based on the
client ip address is used to determine the destination channel. This allows connecting
one client always to the same server (e.g. balancing http sessions to a single server).
.PP
Hosts may be specified either by hostname or by IP address. Ports may
be specified either by name (as listed in /etc/services) or numerically.
If no port is specified in a destination, the destination port 
defaults to the source port that 
.I balance
controls.
.PP
.I Balance 
allows the specification of the maximum number of connections per channel. This
parameter can be optionally added after the port specification separated by a
colon (":"). If a maximum number of connections is specified a channel will
only be used for this maximum number of simultaneous connections. A maxc value of 0
denotes an unlimited number of connections. This is the initial default value
of a channel.
.PP
The maximum number of groups and channels
.I balance
can handle is specified at compile time and is initially 16 channels in 16 groups. 
.PP
Failover to another destination (a "channel") occurs if the connection is
refused on the current channel or if the connect timeout is reached trying
to establish a connection. If all possible destinations (channels) currently fail,
the client connection to balance is closed. 
.PP
.I Balance
accepts the following options:
.TP
.B a
Enable autodisable option: A channel needs to be manually re-enabled after
a failure.
.TP
.B b
Bindhost:
.I Balance
binds to the specified host (or address) for listen() instead to INADDR_ANY.
.TP
.B B
Bindhost:
.I Balance
binds to the specified host (or address) for outgoing connections (the 
connection will be initiated from this address).
.TP
.B c
Command:
allows to send a command to the balance master process (see interactive mode)
.TP
.B d
Debug:
.I Balance
outputs debugging and tracing information messages on stderr.
.TP
.B H
Hashfailover:
.I Balance
does failover to next node even if hash is used.
.TP
.B F
Foreground:
tells 
.I balance 
to stay in foreground. This might be useful for 
testing and debugging since 
.I balance 
can be stopped in that mode using ^C (or other interrupt character).
.TP
.B M
Use memory mapping for IPC instead of shared memory
.TP
.B i
Interactive Control:
.I Balance
connects to the running instance defined by local port and bind address via
shared memory and allows to control the behaviour of it using a 
command line interface. The access permission using this interface are
determined by the access restrictions of the shared memory segment in effect. 
.I help or "?"
prints out a short command overview, 
.I create
allows to establish a new destination definition (channel) consisting of 
host and port in the current group,
.I disable
disables a channel in the current group,
.I enable
enables a channel again in the current group,
.I group
changes the current group in interactive mode where all following commands
are targeted,
.I hash
changes the current group to be of type "Hash",
.I help 
prints out online help informations,
.I kill
shuts down the master process and exits interactive mode,
.I maxc <channel> <maxc>
sets the maximum number of connection ot the channel (0 means infinite),
.I mrtg-bytes <group> <channel>
prints out the bytes received/sent in MRTG compatible format (intended to be called
with -c automatically by MRTG),
.I mrtg-conns <group> <channel>
prints out the total connections in MRTG compatible format (intended to be called
with -c automatically by MRTG),
.I quit
exits the interactive mode,
.I reset
resets the byte counters of a channel, 
.I rr
changes the current group to be of type "Round Robin",
.I show 
shows an overview and the status of all channels including the incoming and
outgoing transfer volume in bytes. The output is sorted by groups. Additionally
the current connections (c) and the maximum allowed connections (maxc) are printed,
.I version
prints out the version and MAXGROUPS and MAXCHANNELS constants at compile time.
.TP
.B p
Packetdump:
.I Balance
shows all incoming and outgoing data on stdout using a 
simple always readable external representation of data.
This might be useful for debugging and protocol analysis.
.TP
.B t
Connect Timeout:
the default timeout trying to establish a connection to any destination
can be changed using this option. The default timeout after which a
destination is regarded to be currently inaccessible is 5 seconds. 
.TP
.B T
Select Timeout:
Timeout for select(), default = 0 (never). This feature is currently 
untested.
.PP
.SH EXAMPLES
.PP
.TP
.B $ balance smtp host1.test.net host2.test.net
Connection to the local SMTP port will be forwarded alterating to 
the SMTP port on host1 and host2.
.I Balance
runs automatically in background.
.PP
.TP
.B $ balance -fp imap mailserver
Connections to the local IMAP port will always be forwarded to the
host "mailserver".
.I Balance
stays in foreground and all data is printed in readable format on 
stdout.
.PP
.TP
.B $ balance -f 8888 host1 10.1.1.1:8000
Connections to the local port 8888 are forwarded alternating to host1, port 
8888 and the host 10.1.1.1, port 8000.
.I Balance
stays in foreground connected to the "controlling tty".
.PP
.TP
.B $ balance imap mailserver1::16 ! mailserver2
Two groups are specified, each containing one channel member. First up to 16
simultaneous connections are forwarded to "mailserver1". As soon as they are
consumed, 
.I balance 
proceeds with the next group (1) which will consume all remaining connections
forwarding them to the imap ort on "mailserver2".
.PP
.TP
.B $ balance pop3 host1 host2 host3 ! failover1
.I Balance
does round robin load balancing for the three hosts in the default group 0
for pop3 services. If all three hosts in group 0 fail, all 
connections are then forwarded to the host "failover1".
.PP
.TP
.B $ balance telnet target.munich.net::1
Here 
.I balance
is used to restrict all connections to exactly one at a time forwarding the telnet port.
.PP
.TP
.B $ balance 8888 localhost::12 ! localhost::4 ! localhost::2 localhost::2 ! localhost:25
This is a simple test, forming 5 groups where balance is self referencing its own
services 20 times. This
is simply a test which definitely can be tried at home. 
.SH BUGS
In case that 
.I balance
is not able to forward the connection to any destination the 
inital connection to balance is always first accepted and
then closed again immediately. This is not in every case the
behaviour that would have been seen directly on the destination host.
.SH AUTHOR 
Thomas Obermair, Inlab Software GmbH (obermair@acm.org)
.PP
Copyright (c) 2000-2006,2007 by Thomas Obermair (obermair@acm.org)
and Inlab Software GmbH (http://www.inlab.de), Gruenwald, Germany.
All rights reserved.
.PP
Balance is released under the GNU GENERAL PUBLIC LICENSE, see the file COPYING
in the source code distribution.