1BALANCE(1) General Commands Manual BALANCE(1)
2
6 balance 3.42 - A simple TCP proxy with load balancing and failover
7 mechanisms.
8
10 balance [ -b addr ] [ -B addr ] [ -t sec ] [ -T sec ] [ -adfpHM ] port
11 host1[:port1[:maxc]] [!|%] [ ... hostn[:portn[:maxc]]]
12 balance [ -b addr ] -i [ -d ] [ -M ] port
14 balance [ -b addr ] -c cmd [ -d ] [ -M ] port
16
18 Balance is a simple, generic "userland" TCP proxy, which allows simple
19 round-robin load balancing and graceful failover between several desti‐
20 nation servers.
21 Balance supports IPv6 on the listening side which makes it a very use‐
23 ful tool for IPv6 migration of IPv4 only services and servers.
24 Balance is available at http://balance.sourceforge.net.
26 Definitions: A possible destination consisting of a host address and a
28 port is called a "channel". A channel is member of a "channel group".
29 Channels are numbered in a group starting with 0. Groups are numbered
30 starting with 0, which is the initial default group.
31 Balance accepts connections on the given port and forwards them to the
33 supplied channels. At least one channel (in the default group) must be
34 specified. If there are two or more channels specified in a group bal‐
35 ance performs a simple round-robin load balancing between the channels.
36 Balance allows the definition of further channel groups. The connection
38 scheme works as follows: balance tries first to establish a connection
39 to a channel in the first group (0), performing the standard round-
40 robin load balancing scheme. If no channel in this group is available,
41 balance proceeds with the next higher channel group. Groups are simply
42 separated with a "!" at the command line at startup and can be con‐
43 trolled interactively with the "group" command.
44 A "%" instead of a "!" as a group separator declares the previous group
46 to be of type "hash". This means that instead of a round-robin algo‐
47 rithm, a hash distribution based on the client ip address is used to
48 determine the destination channel. This allows connecting one client
49 always to the same server (e.g. balancing http sessions to a single
50 server).
51 Hosts may be specified either by hostname or by IP address. Ports may
53 be specified either by name (as listed in /etc/services) or numeri‐
54 cally. If no port is specified in a destination, the destination port
55 defaults to the source port that balance controls.
56 Balance allows the specification of the maximum number of connections
58 per channel. This parameter can be optionally added after the port
59 specification separated by a colon (":"). If a maximum number of con‐
60 nections is specified a channel will only be used for this maximum num‐
61 ber of simultaneous connections. A maxc value of 0 denotes an unlimited
62 number of connections. This is the initial default value of a channel.
63 The maximum number of groups and channels balance can handle is speci‐
65 fied at compile time and is initially 16 channels in 16 groups.
66 Failover to another destination (a "channel") occurs if the connection
68 is refused on the current channel or if the connect timeout is reached
69 trying to establish a connection. If all possible destinations (chan‐
70 nels) currently fail, the client connection to balance is closed.
71 Balance accepts the following options:
73 a Enable autodisable option: A channel needs to be manually re-
75 enabled after a failure.
76 b Bindhost: Balance binds to the specified host (or address) for
78 listen() instead to INADDR_ANY.
79 B Bindhost: Balance binds to the specified host (or address) for
81 outgoing connections (the connection will be initiated from this
82 address).
83 c Command: allows to send a command to the balance master process
85 (see interactive mode)
86 d Debug: Balance outputs debugging and tracing information mes‐
88 sages on stderr.
89 H Hashfailover: Balance does failover to next node even if hash is
91 used.
92 F Foreground: tells balance to stay in foreground. This might be
94 useful for testing and debugging since balance can be stopped in
95 that mode using ^C (or other interrupt character).
96 M Use memory mapping for IPC instead of shared memory
98 i Interactive Control: Balance connects to the running instance
100 defined by local port and bind address via shared memory and
101 allows to control the behaviour of it using a command line
102 interface. The access permission using this interface are deter‐
103 mined by the access restrictions of the shared memory segment in
104 effect. help or ? prints out a short command overview, create
105 allows to establish a new destination definition (channel) con‐
106 sisting of host and port in the current group, disable disables
107 a channel in the current group, enable enables a channel again
108 in the current group, group changes the current group in inter‐
109 active mode where all following commands are targeted, hash
110 changes the current group to be of type "Hash", help prints out
111 online help informations, kill shuts down the master process and
112 exits interactive mode, maxc <channel> <maxc> sets the maximum
113 number of connection ot the channel (0 means infinite), mrtg-
114 bytes <group> <channel> prints out the bytes received/sent in
115 MRTG compatible format (intended to be called with -c automati‐
116 cally by MRTG), mrtg-conns <group> <channel> prints out the
117 total connections in MRTG compatible format (intended to be
118 called with -c automatically by MRTG), quit exits the interac‐
119 tive mode, reset resets the byte counters of a channel, rr
120 changes the current group to be of type "Round Robin", show
121 shows an overview and the status of all channels including the
122 incoming and outgoing transfer volume in bytes. The output is
123 sorted by groups. Additionally the current connections (c) and
124 the maximum allowed connections (maxc) are printed, version
125 prints out the version and MAXGROUPS and MAXCHANNELS constants
126 at compile time.
127 p Packetdump: Balance shows all incoming and outgoing data on std‐
129 out using a simple always readable external representation of
130 data. This might be useful for debugging and protocol analysis.
131 t Connect Timeout: the default timeout trying to establish a con‐
133 nection to any destination can be changed using this option. The
134 default timeout after which a destination is regarded to be cur‐
135 rently inaccessible is 5 seconds.
136 T Select Timeout: Timeout for select(), default = 0 (never). This
138 feature is currently untested.
139
141 $ balance smtp host1.test.net host2.test.net
142 Connection to the local SMTP port will be forwarded alterating
143 to the SMTP port on host1 and host2. Balance runs automatically
144 in background.
145 $ balance -b 2001:DB8::1 80 10.1.1.1 10.1.1.2
147 Balance binds on port 80 of the local IPv6 IP address
148 2001:DB8::1 and distributes connections to the IPv4 addresses
149 10.1.1.1 and 10.1.1.2.
150 $ balance -fp imap mailserver
152 Connections to the local IMAP port will always be forwarded to
153 the host "mailserver". Balance stays in foreground and all data
154 is printed in readable format on stdout.
155 $ balance -f 8888 host1 10.1.1.1:8000
157 Connections to the local port 8888 are forwarded alternating to
158 host1, port 8888 and the host 10.1.1.1, port 8000. Balance
159 stays in foreground connected to the "controlling tty".
160 $ balance imap mailserver1::16 ! mailserver2
162 Two groups are specified, each containing one channel member.
163 First up to 16 simultaneous connections are forwarded to
164 "mailserver1". As soon as they are consumed, balance proceeds
165 with the next group (1) which will consume all remaining connec‐
166 tions forwarding them to the imap ort on "mailserver2".
167 $ balance pop3 host1 host2 host3 ! failover1
169 Balance does round robin load balancing for the three hosts in
170 the default group 0 for pop3 services. If all three hosts in
171 group 0 fail, all connections are then forwarded to the host
172 "failover1".
173 $ balance telnet target.munich.net::1
175 Here balance is used to restrict all connections to exactly one
176 at a time forwarding the telnet port.
177 $ balance 8888 localhost::12 ! localhost::4 ! localhost::2 localhost::2
179 ! localhost:25
180 This is a simple test, forming 5 groups where balance is self
181 referencing its own services 20 times. This is simply a test
182 which definitely can be tried at home.
183
185 In case that balance is not able to forward the connection to any des‐
186 tination the inital connection to balance is always first accepted and
187 then closed again immediately. This is not in every case the behaviour
188 that would have been seen directly on the destination host.
189
191 Thomas Obermair, Inlab Software GmbH (obermair@acm.org)
192 Copyright (c) 2000-2007,2008 by Thomas Obermair (obermair@acm.org) and
194 Inlab Software GmbH (http://www.inlab.de), Gruenwald, Germany. All
195 rights reserved.
196 Balance is released under the GNU GENERAL PUBLIC LICENSE, see the file
198 COPYING in the source code distribution.
199 2008/04/08 BALANCE(1)